Introduction: Invertebrate Phyla
? 97% of all animals are invertebrates.
? 85% of the total number of animals are insects.
? Taxonomy- the naming of organisms.
? Systematics- the organizing of organisms into categories.
? Some zoologists like Barnes recognize 33 categories of invertebrates.
? These categories are made up by their uniqueness from each other.
? More is known about animals that are hard than ones that are soft because they are able to fossilize better.
? The more we know about an animal (i.e. arthropods) means that the arthropods will have more complicated categories.
Description of the coastline of the Northeastern United States
? There are sounds which are created on the mainland side of a barrier island.
? They consist of brackish water that is
created by rivers flowing into them from the mainland, and by seawater
that flows towards the land.
? The salinity (on the sound side) and the wave
action (on the outside of the barrier island) make different marine
environments and cause different organisms to be found.
? This coastline has no bedrock, and there are few rocky intertidal areas, most of which are manmade (i.e. jetties, sea walls, and bridges).
? Here there isn’t a big difference between
high tide and low tide.
? Success-
being extant, and not extinct. An animal is successful or not
depending on its options.
? For example, a sponge has less options than a
squid, but they both, along with other animals, have a lot in common.
? For example, water balance, removal of
wastes, and reproduction.
? Marine invertebrates have different problems
than freshwater invertebrates.
? Complicated behavior can only be seen if the organism has a complicated morphology, and or physiology.
? For example, a crab has more complicated
behavior than a sponge because it has more complicated morphology and
physiology than the sponge.
Reproduction
? Seawater is better for external fertilization than freshwater is, and even better than the land is because the eggs and sperm are more like the seawater that they are in.
? The animals that release their gametes into the water are dieous, and this describes most of the marine invertebrates.
? Some marine invertebrates have internal fertilization such as cephalopods.
? There is internal fertilization where there are stressful conditions such as a constant salinity.
? In the estuaries where the salinity fluctuates is where there is external fertilization.
Development
? Direct development- when a juvenile grows to be an adult but the difference between the juvenile and the adult is very small (i.e.
turtles and turtle’s young).
? Indirect development- when the young is very different from the
adult because of their larvae (i.e. a tadpole to a frog, a caterpillar to
a butterfly).
? It must involve a metamorphosis usually.
? In this type of development, there is a life
history, and the larvae may be planktonic and metamorphose into another
larvae before becoming an adult.
? Different organisms may have direct, or
indirect development, and this is one way of seeing relationships between
different groups or categories of animals.
Two Theories
? 1. Maybe all animals had different ancestors.
? This is called polyphyletic.
? 2. Maybe all animals had a common ancestor.
? This is called monophyletic.
? Evolution can be seen by seeing if an organism is polyphyletic or monophyletic, from the fossil record, or by tissue formation, or by physical, or biological means.
? Mesozoans probably had the same ancestors.
? No one knows which one gave rise to multi celled organisms.
? Fossils, biochemistry, and developmental biology are different ways of trying to find out what gave rise to what.
Basic Marine Ecology
? The intertidal region has tides that come in (which are not exposed to the air) and tides that come out (which are exposed to the air).
? Semidiurnal- the tide increases and decreases twice everyday.
? Spring tide- when the moon is new or full which creates a high tide.
? Neap tide- when the moon is at half or quarter phase.
? Subtidal organisms are never exposed to air.
? Epifauna- organisms that live on something.
? Epiflora- plants that live on something.
? Infauna- animals that burrow in mud, clay, sand, and even rock, wood, and calcareous skeletons.
? Both epifauna and infauna organisms experience different conditions even if the epifauna and infauna organisms are located at the same location of the intertidal area.
? Infauna aerobic animals have to keep in touch with air through the water.
? At low tide they can’t do this so they build tubes.
? Geotome- a shovel, used to find infauna.
The Parazoa: Porifera
? Two kinds of multi-celled animals:
? 1. Sub kingdom Parazoa which contains the Phylum Porifera, the sponges
? 2. Sub kingdom Metazoa which contains all other phyla
? Note: Sponges aren’t metazoans.
? Parazoans and metazoans both have separate ancestors
? Note: Parazoans and metazoans aren’t related
? The choanocytes (collar cells) cause water to move through the microvillus and up to the flagella and away.
? The large items are carried away and the small bacteria and algae are caught in the microvilli and are moved down and digested.
? The archeocytes can also digest and or carry the food to another area and ingest it.
? Non living sponge cells are spicules.
? There is a problem using the term spongocoel because coel refers to coelom which a sponge doesn’t have so the term atrium is now used.
? Ostium- a hole or pore. Not to be confused with the porocyte which is the tube connected to the ostium.
? This type of sponge design is called an asconoid. A sponge that has this is called the genus Leucoselenia.
? Asconoid sponges have a problem because any water that comes in is only filtered by choanocytes and mostly there isn’t any filtration because the water is on its way out of the osculum.
? Because of this, asconoid sponges are very small.
? This type of sponge design is better because there are more choanocytes which means more filtration than was found in the asconoid sponges.
? This type of sponge is called a syconoid sponge.
? This sponge is bigger than asconoid sponges because of its better filtration.
? These also don’t get very big.
? It includes the genus Scypha and Grantia.
? They get 3-4 cm tall at the most, and are cylinder in shape.
? Some sponges had structure that make them rigid other than the spicules and this substance is called spongin fibers.
? They are made by archecytes.
? Sponges can have:
? 1. spicules
? 2. spongin (bath sponges)
? 3. all of the above
? Some spicules are made of CaCO3 (calcium carbonate) and others are of SiO2 (silica)
? 1. calcareous (can be dissolved in acid)
? 2. siliceous (can’t be dissolved in acid)
? Note: This type of sponge has lots of oscula.
? This type of sponge can be radial like others, it is asymetric mostly.
? There is a lot of water driving and water filtering potential because there is more water passing through more choanocytes.
? This type is called leuconoid.
?
? The large hole at the top of this sponge isn’t the oscula because within that hole are many oscula.
? No other animal has choanocytes.
? The choanoflagellates which are unicellular are the closest thing to the choanocytes.
? Sponges are constructed at the cellular level.
? They don’t have tissues, the closest thing that they have to tissues are the pinacocytes.
? If sponges are strained through a silk net, they can still survive by getting back together.
? This is their flexibility or plasticity.
? Archeocytes can become any cell that the sponge has.
? Choanocytes can become archecytes, or gametes.
? When a male sponge is sexually mature, some choanocytes become sperm, swim out and end up in the female and the female’s choanocytes have become eggs.
? Embryos develop in the radial canals or choanocyte chambers.
? This is unique because gametes usually arise from gonads in other animals.
? Most sponges are dioecious, some are monoecious.
? They reproduce asexually and sexually too.
? Sponge fisherman cut them into pieces, tie them to rope, and place them in the water
? Fresh water sponge reproduction is complex.
? A package of sponge archeocytes are called gemmules.
? When they are formed, the sponge dies and the gemmules grow when the conditions are good.
? Marine sponges have gemmules also.
? The majority of sponges are marine, in low shallow water but some are found deep in the water.
? Sponge cells of different sponges in the same species can combine into one sponge.
? Sponges are eaten by some animals but some chemicals keep predators away such as stinking sponges and garlic sponges.
? Sponges want hard substances to attach to and they compete with other sponges for these places.
? They are used in pharmacudicals.
? Class Calcarea (CaCO3). If spicules dissolve in acid, it’s a calcareous sponge.
? They are asconoid, syconoid, and leuconoid with the majority being acon and syconoid.
? Class Hexactinelliala (SiO2)(glass sponge). Spicules are glass.
? They are long and the spicules are fused.
? They have multi nucleate choanocytes and this might make them another phyla all together.
? They aren’t asconoid, syconoid, or leuconoid.
? Class Demospongiae (SiO2). They are siliceous because of their spicules, and are composed of spongin.
? They are only leuconoid, and this is why they become so large.
? “Class” Scelerospongiae (SiO2, CaCO3). It is found in the book. They have spicules that are siliceous, and spongin fibers and a calcareous outer surface that is thin.
? Scelero- hard.
? Scelerosponges occur around demo and calcareous sponges.
? This class isn’t to be worried about because it’s on its way out.
? It has appeared mostly in the fossil record.
? In quiet water, sponges grow tall, and have a radial shape.
? In rough water, the sponge may be low.
? Both types can be seen in the same genus and species.
? If they are transplanted from still to fast water or vice versa, its morphology will change to the appropriate shape.
Metazoans
? A trend that they have is an outer covering that is epithelical and separates the interior of the organ from the external world.
? This cover makes organs become different inside than they are one the outside.
? Now organs and organ systems can control conditions in the inside of the organism.
? The development of the digestive system, circulatory system, and etc. gives organisms an interior environment that is different from the outside.
? Only the body temperature remains similar to the outside.
Phylum Cnidaria
? These animals have tissues. They are at the tissue grade of construction. The cells make a tissue layer.
? Tissue- a layer of cells of the same type.
? One may same that cnidarians lack this because their tissues have many different types of cells.
? An outer layer called ectoderm and an inner layer called an endoderm or (gastroderm).
? Ectoderm is made of many cells:
? Epithelio- muscle cells. At the their bases are contractile elements.
? In between them are:
? Gland cells- cells that make mucus, and calcium carbonate.
? Small cells that fill in spaces of large cells are called interstitial cells.
? Sensory cells are responsive to stimulation (chemical and physical). The foot of the epithelio muscle cells are neuronal cells.
? Cnidocytes are cells that make the organelle that contains the stinging cell. That organelle is called a nematocyst which is in a nematocyst capsule.
? Cnidocil are modified cilia that work as a trigger.
? The nematocyst consist of a bladder and when the nematocyst discharges, the thread comes out turning inside out.
? Once the thread is all of the way out, you can see barbs on the outside, but when the thread is in the bladder, the barbs are on the inside.
? The thread goes through skin and exoskeletons.
? There are three types:
? 1. Penetrants or (stinging nematocysts). They also have venom
? 2. Glutinants- tentacles that stick to things such as prey
? 3. Volvents- tentacles that wrap around things such as prey
? Cnidocytes make nematocysts.
? Pelagic octopus use the tentacles of Portuguese man-of-war as defense.
? Cnidocytes are found on the tentacles around the mouth, and in the mouth of all cnidarians except the hydra.
? Nematocysts are also under neuronal control.
? If the animal is full of food and comes in contact with prey, it may not fire as many nematocysts as it would if it were starved.
? There is also a difference in firing between sea anemone that are attached to a rack, and sea anemone attached to a snail.
? In the interior there are large nutritive-muscle cells that are for digestion but have some contraction ability.
? Gland cells are found inside, and interstitial cells.
? We just discussed the outer and inner epidermal tissue. Between them is the mesoglea.
? It may have neuronal, ameboid cells in it in some forms.
? In the jellyfish it is the bulk of the animal, and this is where the name jellyfish comes from.
? A feature that describes the phylum is polymorphism.
? One reproduces asexually and the other sexually.
? This is alternation between the two us called metagenesis or metagenetic.
? Coelenteron- a gut with one opening, the mouth.
? The evolution of cnidarians uses different combinations of the above.
? Freshwater Hydrozoans have a polyp, that is dominant, and a medusa form.
? In the Scyphozoa, the medusa is dominant, and the polyp isn’t.
? In the anthozoans, there is no medusoid form.
Class Hydrozoa
? Order Hydroida (hydroids)
? Order Siphonophora (Portugeuese man-o-war)
? In the polyp phase, the polyps look like hydra but the mouth is at oral end and not the aboral end.
? Parts are radial around the oral-aboral axis (vertical axis). Because of this, they are called radiata but they are not really radial.
? Manubrium- located by the mouth.
? The polyps are solitary. The aboral end is known as the foot or pedal.
? Most are solitary, but are colonial.
? In different species, colonies are different.
? The gastrozooid isn’t covered by theca or perisarc because it stops at the base of the gastrozooid which makes it a gymnoblastea- naked polyp.
? Suborder Gymnoblastea (anthomedusae)
? Anthomedusae refers to medusa. The gymnoblastea (anthomedusae) ends look like this:
? The other suborder:
? Suborder Calyptoblastea (Leptomedusae)
? These hydra are covered by thecal/perisarc material and look like this:
? Phylum Cnidaria
? Class Hydrozoa
? Order Hydroida
? Suborder Calyptoblastea (Leptomedusae)
? Suborder Gymnoblastea (Anthomedusae)
? The production of medusa is asexual and medusae look like this:
? When combined, there is a planula.
? The medusoid stage is sexual.
? Most hydroids are dioecious.
? Leptomedusae- disk medusae. They are disk shaped or flat, short in oral-aboral axis.
? Ocellus- photoreceptors
? Craspedote- jellyfishes with a velum.
? Scyphomedusae lack a velum and are acraspedote.
? Hydractinia echinata (hermit crab hydroid)- settles on hermit crab shells and grows horizontal and covers over the surface.
? It has gastrozooids/gonophores and zooids that have tentacles with nematocysts called tentaculozooid.
? There is also dactylozooid.
? Note this polymorphism. They are modified polyps that make them different from other polyps.
? Order Siphonophora (not jellyfish)
? Physalia physalis
? Starts as planula which makes a float (a gas filled modified medusa).
? The a budding zone develops and doesn’t separate from the float.
? Gastrozoids, tencalculazooids
? Fishing tentacles develop
? Tentacles can get 100 feet long
? Gastrovascular cavity- stomach of Gonionemus
? Hydroids move by muscle contractions of the brim.
? Patterns of reproduction in Hydrozoans.
? Polyp => Medusa (asexual by budding)
? Polyp => Medusa (sexual) gametes
? Gametes => Plannula Larva
? Larvae => Polyp
? The above is primitive, and some hydrozoans still do it.
? One way:
? Polyp with medusa is budded off.
? Obelia and Eudendrium have separate gastrozooids/gonozooids.
? Halacordyle have medusae from gonophores on mannubrium.
? Another way:
? Polyp with no medusae.
? Hydractinia sends sperm to female gonozooid which leads to free plannula.
? Tubularia sends sperm to female gonophores which leads to the development of actinula larvae.
? Rather than a plannula larva it has a larval form that looks like a hydrant called an actinula larva.
? Hydrant- a hydroid with tentacles.
Class Scyphozoa
?
? These animals can get to a meter in diameter (the bell).
? Stomalophus is a cannon ball, or cabbage head jellyfish. Its bright brown when alive, white when dead.
? Their medusa are more complex. The mouth is enclosed in four tentacles.
? The margin of the bell has small tentacles.
? The gastrovascular cavity is lined with nematocysts.
? Radial canals radiate out to the margin.
? Aurelia aurita. Its margins are tan, gonads are tan, and the rest of the body is light tan.
? Gonads are gastrodermal or endodermal and developed in pouches called a gastrovascular cavity.
? A radial canal system transports liquid materials through the body from the gastrovascular cavity.
? Their body is more nurished than hydrozoans because of this.
? Jellyfish are 98-96% water.
? The contractile epithelical muscle cells are well developed for swimming.
? When food is caught, it goes to the margin where the oral arm sweeps the margin and brings the food to the mouth.
? Some have symbiotic algae in the tentacles.
? Cassiopeia is found in the mangrove areas and it lays on its exumbrellas and catches food as it goes down.
Class Cubozoa
? This class includes dangerous jellyfish.
? Most are diocecious. Gametes are produced by gonads, fertilization is external but some times internal in the gastrovascular cavity.
Class Anthozoa
? Hydrozoa are bell animals.
? Scyphozoa are disk animals.
? Anthozoa are flower animals.
? The class is divided into two subclasses:
? Subclass Zoantharia (Hexacorallia)
? They are in multiples of six.
? It includes sea anemones and hard corals.
? Order Actiniaria (sea anemones)
? Order Scleractinia (madrepodaria) the stony, hard corals (reef builders)
? Subclass Alcyanaria (Octacarallia)
? The octacorals or soft corals. They are in groups of eight.
? Order Gorgornacea- sea whips, sea fans
? Order Pennatulacea- sea pens, sea pansy.
? They are more complex than hydrozooid polyps.
? There is no medusa stage!
?
? The tentacles are hollow for communication.
? Complete septum- septum that fuse to the pharynx from the body wall.
?
? Septal filament- a septa that doesn’t fuse with the pharynx.
? Septa are paired and have the same type on the opposite end of the pharynx.
? Incomplete septa- septa that don’t fuse to septa.
? In scyphozoa and anthozoa their muscles are endodemally derived but in the hydra they are extrodermally derived.
? Gonads are internal and endodermally derived.
? Acontium- threads of nematocysts.
? The complete septa provides the limit that the sea anemone can expand laterally.
? Gullet- the inside of the pharynx.
? Siphonoglyph- a place where water is pumped by cilia action.
? This is the way that it relaxes after contraction downward.
? Acontium can come out of the mouth for protection.
? Not all sea aneomone have acontium.
? The retractor muscles are facing one another on a pair of septa.
? The elongations are made by muscles working on the fluid in the body.
? The foot is sticky because of discharge of nematocysts or glandular secretions.
? They can move and some can somersault using their tentacles to hold.
? Some can swim with movement of tentacles.
? The nervous system is multipolar.
? The nervous system scattered which makes a nerve net surrounding the body. This accounts for their behavior.
? Sperm and eggs are released in water (external, sometimes internal).
? They are dioecious, some are monoecious.
? They can also reproduce asexually by binary fission or budding which then buds completely.
? As they move, they leave pieces of themselves behind the foot that grows into adults which is called pedal laceration.
? They are mostly solitary and not colonial.
? Order Scleractinia (hard ray)
? Scler- hard
? Aclinia- ray
? They are strong and hard corals, true corals.
? They can calcify and make a true exoskeleton of CaCO3.
? Most are colonial and few are solitary.
? Calyx- the depression where the coral sits.
? Scleroseptum- the external rays of a mushroom coral.
? These coral bud off one another but the budding is incomplete because the parent and child do not separate from each other and have the same gastrovascular cavity.
? Coral reefs are tropical and are found in no less than 20oC.
? The Gulf Stream brings warm water.
? The water must be clear and shallow.
? 50 meters from the surface and 70 meters in clear water is too deep.
? This is because they depend on symbiotic algae found in the bridges between polyps and in pedal disks and they are dinoflagellates.
? Genus Symbiodinium is the genus of these algae, also called zooxanthellae.
? They are in the endoderm of these coral.
? Hermatypic coral has the algae.
? They need warm water because CaCO3 dissolves in cold water.
? They need clear water and shallow water so that he sun can penetrate the water and reach the coral.
? When the light doesn’t penetrate well (deep areas), the coral has a larger surface area and it is wide.
? In shallow areas it is thin and high.
? Aiptasia pallida is a sea anemone.
? The large number of septa increases the surface area.
? The septum in hard coral is for protection.
? Subclass Alcyanaria (octacorllia)
? They are colonial and the polyps all have 8 tentacles and when they are expanded, they are pinnate.
? They have only siphonoglyph.
? There are 8 complete septa inside.
? The mesoglea is complicated because its ameboid and can produce a skeleton.
? The outside is ectoskeleton in origin.
? The inside is endoskeleton in in origin.
? In the order Gorgonacea called Gorgonians.
? Sea whips and fans are found here.
? There is an axial support called an axial skeleton which is made of polysaccarides.
? The skeleton is tough but flexible as well.
? Ceenchyme- modified mesoglea that makes ossicals/spicules.
? The color and they way they are interlocked varies.
? Their skeleton is different because its internal, unlike that of other anthozoans that have an external skeleton.
? All polyps are inter connected by tubes known as solenia.
? Sea fans are more flexible and they are more connected and are at right angles to the current.
? Order Pennatulacea includes sea pansies and sea pens. They are soft and more fleshy.
? All anthozoans are polyps.
? Sexes are separate.
? Fertilization is external in marine species, it may be internal in freshwater species.
? They have plannula larvae.
Phylum Ctenophora
? The comb jellies.
? They are similar to cnidarians.
? They have endodermal, mesodermal, and ectodermal layers.
? They are spherical and some are in a long band (venus’ girdle).
? Tentacles have no nematocysts but colloblast.
? On the organisms’ surface there is a longitudinal band of cilia on the outside of meridional canals and each row has overlapping plates and fused cilia.
? Ctene- comb
? Etenephora- comb bearer
? They have flickering which distinguish them from jellyfish by sight.
? They eat clam and oyster larvae and are a problem to the seafood industry.
? They are bio-luminescent when they are disturbed.
? Cnidarians and Ctenophores are radial symetrical.
? Sea anemones with the siphonoglyphs become biradial because they are only mirror images of each other if cut on the places shown.
? General Concepts
? Cnidarians are two germ layers.
? In ctenophores, there is a third tissue layer but not a germ layer.
? All the rest of the organisms have three tissue layers:
? Ectoderm
? Mesoderm
? Endoderm
? Endoderm creates the gut, ectoderm creates the skin and nervous system, mesoderm creates the muscles, circulatory system, blood, heart, and bones (skeletal system).
? In the cnidarians, muscles are created by ectoderm and endoderm.
? In anthozoans and scyphozans, muscles are created by mesoderm.
? The development of mesoderm opened up some new options and created triptoblastic organs.
? When cell division takes place early, cells do like this:
? In other kinds of organisms there is a difference:
? The daughter cells are not equal to mother cells (they are smaller) and instead of being right behind each other, they are oblique to the one before.
? Cells that are unequal in size are called inequal.
? When the embryo separates into a two celled stage you have identical twins.
? Cells that can do everything that other cells can do in an embryo are called indeterminate.
? If cells at the two cell stage are separated and neither would survive, it is called determinate.
? Because of this, there can be no identical twin oysters.
? Animals can be divided by the above characteristics.
? All mesoderm in spiral radial organisms is made by micromere 4d called mesentoblast.
? The ectoderm is produced by micromere 1-3 and their progeny.
? The endoderm is produced by 4 A B C D (4th quartet macro), 4 a b c d (4th quartet micro)
? The mesoderm is produced by 4d (4 quartet micro).
? The above is why there can be no identical twin snails.
? At the 4th quartet stage it’s at the blastula stage.
? Blastopore- a hole in the blastula (ball of cells)
? If the blastopore becomes the mouth it’s called a protostome.
? If the blastopore becomes the anus, it’s called a deuterostome.
? Protostomate organisms have:
? Spiral cleavage
? Inequal cleavage
? Determinate development
? Blastopore- mouth first
? Deuterostomate organisms have:
? Radial cleavage
? Equal cleavage
? Indeterminate development
? Blastopore doesn’t become the mouth first, it is the mouth second and the anus first.
? Protostomes are mostly invertebrates except echinoderms, pogonophorans, and chordates.
? If an organism is in cross-section you should see the gut, if there is one, and:
? The comb jellies.
? They are similar to cnidarians.
? They have endodermal, mesodermal, and ectodermal layers.
?
? They are spherical and some are in a long band (venus’ girdle).
? Tentacles have no nematocysts but colloblast.
? On the organisms’ surface there is a longitudinal band of cilia on the outside of meridional canals and each row has overlapping plates and fused cilia.
? Ctene- comb
? Etenephora- comb bearer
? They have flickering which distinguish them from jellyfish by sight.
? They eat clam and oyster larvae and are a problem to the seafood industry.
? They are bio-luminescent when they are disturbed.
? Cnidarians and Ctenophores are radial symetrical.
? Sea anemones with the siphonoglyphs become biradial because they are only mirror images of each other if cut on the places shown.
? General Concepts
? Cnidarians are two germ layers.
? In ctenophores, there is a third tissue layer but not a germ layer.
? All the rest of the organisms have three tissue layers:
? Ectoderm
? Mesoderm
? Endoderm
? Endoderm creates the gut, ectoderm creates the skin and nervous system, mesoderm creates the muscles, circulatory system, blood, heart, and bones (skeletal system).
? In the cnidarians, muscles are created by ectoderm and endoderm.
? In anthozoans and scyphozans, muscles are created by mesoderm.
? The development of mesoderm opened up some new options and created triptoblastic organs.
? When cell division takes place early, cells do like this:
? In other kinds of organisms there is a difference:
? The daughter cells are not equal to mother cells (they are smaller) and instead of being right behind each other, they are oblique to the one before.
? Cells that are unequal in size are called inequal.
? When the embryo separates into a two celled stage you have identical twins.
? Cells that can do everything that other cells can do in an embryo are called indeterminate.
? If cells at the two cell stage are separated and neither would survive, it is called determinate.
? Because of this, there can be no identical twin oysters.
? Animals can be divided by the above characteristics.
? All mesoderm in spiral radial organisms is made by micromere 4d called mesentoblast.
? The ectoderm is produced by micromere 1-3 and their progeny.
? The endoderm is produced by 4 A B C D (4th quartet macro), 4 a b c d (4th quartet micro)
? The mesoderm is produced by 4d (4 quartet micro).
? The above is why there can be no identical twin snails.
? At the 4th quartet stage it’s at the blastula stage.
? Blastopore- a hole in the blastula (ball of cells)
? If the blastopore becomes the mouth it’s called a protostome.
? If the blastopore becomes the anus, it’s called a deuterostome.
? Protostomate organisms have:
? Spiral cleavage
? Inequal cleavage
? Determinate development
? Blastopore- mouth first
? Deuterostomate organisms have:
? Radial cleavage
? Equal cleavage
? Indeterminate development
? Blastopore doesn’t become the mouth first, it is the mouth second and the anus first.
? Protostomes are mostly invertebrates except echinoderms, pogonophorans, and chordates.
? If an organism is in cross-section you should see the gut, if there is one, and:
Comparative vertebrate morphology deals with vertebrate anatomy and its significance
Comparison deals with similarities and differences and helps us formulate questions
For example, salmon, tuna, and trout have one tail shape and sharks have another.
Why do salmon, tuna, and trout have one tail shape and sharks have another tail shape?
The functional requirements of the tail in salmon, tuna, and trout is different in sharks.
Form allows function. The two are coupled.
Vertebrate design is complex and precise. To many early morphologists, this implied the intervention of a divine hand (God). However, not everyone believed this.
The study of morphology has been divided between those scientists centered on evolution and those centered on structure.
To some extent, the principles of both evolution and structure have grown from different people with different views. To understand this, we need to examine the historical development of morphology.
Historical Predecessors-Evolution
Before Charles Darwin, Anaximander developed ideas about the change from fishlike, scaly animals to land animals.
Empedocles said creatures came together oddly (humans with cow heads) and only those that came together correctly lived.
Charles Darwin did not propose that species evolve, he proposed the conditions for and the mechanism of this evolutionary change.
He proposed three conditions:
1.Species increase naturally in number
and this number is limited by resources.
2. There is competition for resources.
3. Only few survive
These conditions are the mechanism that determines which organisms survive and which do not. It is called natural selection-
nature’s way of weeding out the less fit.
The controversy over evolution emerges at three levels: fact, course, and mechanism.
1.Did evolution occur?
2.What course did evolution take?
3.What mechanism produced evolution?
Carolus Linnaeus believed that species did not change and that evolution didn’t occur.
Jean-Baptiste de Lamarck believed that
1.species changed through time
2.change from the “lowest” to the “highest”
3.the mechanism of change was need
Alfred Russel Wallace and Charles Darwin independently said animals with favorable adaptations would compete better than other animals for limited food (natural selection).
Historical Predecessors-Morphology
Although some anatomists like T.H. Huxley believed in evolution, others did not.
Georges Cuvier believed that evolution could not occur because if an organism’s body part were changed it would destroy the harmony among the parts and their function and would lead to death of the organism.
Richard Owen also opposed evolution. He believed similar bone patterns in bat wings, mole forelimbs, and dugong flippers were the result of archetypes. Archetypes- biological blueprints, plans upon which organisms are built. Particular functional needs would cause differences in plans.
These plans are repeated in an individual.
Although T.H. Huxley agreed all vertebrate skulls are made from the same plan, he said the plan is not repeated in the vertebrae.
Although issues raised by morphologists such as Owen and Cuvier tend to be forgotten, more than evolution is needed to explain biological design. Morphology, too, must also be seen as a cause of design.
Not all evolutionary changes are equally probable because not all morphologies are equally available to natural selection.
Biological design is not due to DNA alone.
To analyze design, there are concepts of form, function, and evolution.
FORM
Form has similarity, symmetry, and segmentation.
Similarities
In different organisms, corresponding parts may be considered similar to each other by 3 ways: ancestry, function, and appearance.
Homology: when two or more features share a common ancestry
Analogy: when features share a common function
Homoplasy: when features look alike but don’t share ancestry or function
Serial homology: when there is similarity between repeated parts in the same organism
Symmetry
Symmetry: it describes the way in which an animal’s body meets the environment.
Medial: the midline of the body.
Lateral: the sides of the body.
For an attached appendage:
Distal: the region farthest from the body.
Proximal: the region closest to the body.
Pectoral region: chest, supports forelimbs.
Pelvic region: hips, supports hindlimbs.
Frontal plane: divides a bilateral body into dorsal and ventral sections.
Sagittal plane: splits a bilateral body into left and right portions.
Transverse plane: (coronal plane) separates a bilateral body into anterior and posterior.
Anterior:
Posterior:
Superior: cranial of a human (the head).
Inferior: caudal of a human (the feet).
Segmentation
Segmentation: a body or structure built of repeating or duplicated sections.
Segment: (metamere) each repeated section.
Metamerism: the process that divides a body into duplicated sections (segmentation).
FUNCTION
Function: the action of a part as it works in an organism.
Biological role: the way the part is used in the environment during an organism’s life.
EVOLUTION
Phylogeny: the course of evolution
Dendrograms: graphic schemes that summarize phylogeny (course of evolution).
After the concepts of form, function, and evolution, the analysis of design has 3 steps:
1.The question (done in the laboratory)
2.The function (done in the laboratory)
3.The biological role (done in the field)
The tools used to define the question are:
1.Dissection: the anatomical description of
an animal’s structural design
2. Taxonomy: the proposed relationships of
an animal (and its parts) to other species
The tools to determine how structure performs within an organism are:
1.Radiography: X-rays
2.Video tape or film
3.Cannulae: thin tubes inserted in blood
vessels to study the circulatory system
4. Radiopaque fluids: fed to animals to study
the digestive tract
5. Electromyography: inserting electrodes
into muscles to measure electric charges
The tools to discover the adaptive or the biological role of a part are:
1.Ecomorphology: using ecological analysis
(careful observation of the organism in its environment) in the examination of a morphological system
PHYLUM CHORDATA
Fourth largest phylum in terms of species #
Humans belong to this phylum
CHORDATE PHYLOGENY
Embryonic Development
The egg begins to divide repeatedly after fertilization, a process termed cleavage.
In some animals, dividing cells of the embryo are offset from each other, a pattern known as spiral cleavage.
In others, the dividing cells are aligned, a pattern termed radial cleavage.
At this point, the embryo is little more than a clump of dividing cells that soon become arranged into a round, hollow ball known as a blastula.
The ball has walls made of cells that surround the fluid-filled cavity within.
One wall of this ball of cells begins to indent and grow inward. The opening into this indentation is the blastopore.
The indented cells themselves are destined to become the gut of the adult. Indentation continues until cells reach the opposite wall, where they usually break through, forming a second opening into the primitive gut (the blastopore being the first).
At this point in embryonic development, the now multicellular embryo is composed of three basic tissue layers:
1.an outer ectoderm
2.an inner endoderm that forms the wall of the gut
3.a mesoderm that forms the layer between the two.
If the solid sheet of mesodermal cells splits to form the body cavity within them, the result is a schizocoelom.
If, instead, sheets of mesoderm form outpocketings of the gut that pinch off to form the body cavity, the result is an enterocoelom.
Protostomes, literally meaning “first mouth,” are animals in which the mouth arises from or near the blastopore. Additionally, they tend to have spiral cleavage, a schizocoelom, and a skeleton derived from the surface layer of cells.
Deuterostomes, literally meaning “second mouth,” are animals in which the mouth arises not from the blastopore but secondarily at the opposite end of the gut (the blastopore itself becomes the anus).
Additionally, embryonic development of deuterostomes includes radial cleavage, an enterocoelom, and a calcified skeleton, when present, derived generally from mesodermal tissues.
CHORDATE ORIGINS
Chordates ancestors are extinct.
Living groups are studied for possible clues that they retain of ancestral relationships.
This involved looking for similarities in anatomy and embryology.
One such view traces chordate origins back to annelids and arthropods.
Chordates from Annelids and Arthropods
Annelids and arthropods share with chordates similarities of basic body design:
1.all three groups are segmented
2.all have similarities in gross brain regionalization (forebrain and hindbrain)
3.all have similar body designs
(in chordates it is upside down)
Major weaknesses of this proposal:
1.nerve chord of annelids and arthropods is solid and not hollow as in chordates
2.inverting an annelid or arthropod to a chordate involves moving mouth and anus
3.annelids and arthropods are protostomes and chordates are deuterostomes
Chordates from Echinoderms
Chordates came from echinoderms because:
1.both groups are deuterostomes
2.both (larval echinoderms) are bilateral
3.larval echinoderms are similar to larval
hemichordates
Vertebrates are proper chordates- they have all four chordate characteristics at some time during their lives.
The early vertebrates had a strengthened notochord for body support and locomotion
Vertebrates had some innovations:
1.the vertebral column
2.the cranium
INNOVATIONS
Vertebral Column
Inspired the name vertebrates, composed of:
Vertebrae- a series of separate bone or cartilage blocks firmly joined as a backbone that defines the major body axis
Intervertebral disks- thin compression pads that are between successive vertebrae
A typical vertebra consists of:
Centrum- a solid cylinder that encloses the notochord
Dorsal neural arch- encloses the spinal cord
Ventral hemal arch- encloses blood vessels
Neural and hemal spines- extensions of the dorsal neural and ventral hemal arches
When vertebrae first appeared, the notochord continued to serve as the major structural component in the animal’s body
As the role of the vertebral column enlarged, that of the notochord declined.
In adults of most complex vertebrates, the embryonic notochord disappears.
But in mammals the notochord persists only as a gellike core called a nucleus pulposus.
INNOVATIONS
Head
Cranium- a structure of bone or cartilage that supports sensory organs in the head and encases or partially encases the brain
The head develops from neural crest cells- embryonic cells found only in vertebrates
Although some vertebrates lack vertebrae, all have a cranium and some scientists prefer the term craniates rather than vertebrates
ORIGIN OF VERTEBRATES
Evolution of early vertebrates was hypothesized to proceed in three steps:
1.a suspension-feeding prevertebrate
(cilia made a food-bearing current)
2. an agnathan- a vertebrate without jaws
(muscular pump made food current)
3. a gnathostome- a vertebrate with jaws
(muscularized mouth snatched prey)
Step 1: Prevertebrate
Prevertebrates were suspension feeders that used a ciliary pump like hemichordates, urochordates, and cephalochordates did.
The shift from a prevertebrate to a vertebrate condition involved two mechanical changes in the pharynx to make the muscular pump:
1.the pharynx developed an encircling band
of muscles (contraction=water out of slits)
2. cartilage replaced the collagen of the
pharyngeal bars (relaxation=water in)
Step 2: Agnathan
Agnathans were deposit feeders- they pushed their mouths into mud and used a muscularized pharynx to draw in sediment rich in organic particles and microorganisms
Step 3: Gnathostome
They were raptorial feeders- they removed individual, motile food particles selectively from suspension or off surfaces.
With motile food, raptorial feeding favored:
1.expansion of the pharyngeal pump
2.mouth closure (jaws for anti-food escape)
VERTEBRATE CLASSIFICATION
Vertebrates are divided into four groups:
1.Agnathans- fishes without jaws (lack rigid hinges that support borders of the mouth)
2. Gnathostomes- fishes with jaws
3. Tetrapods- four-footed (quadrupeds)
(amphibians, reptiles, mammals); or descendants of 4-footed ancestors (legless
reptiles, amphibians, mammals, and birds)
4. Amniotes- embryos made in an amnion-
a delicate, transparent, saclike membrane
that encases the embryo in water (for
protection) (reptiles, birds, and mammals)
Anamniotes- those without an amnion
(fishes and amphibians)
AGNATHANS- jawless fishes that lack a biting apparatus
Conodonts- early agnathans that had conodont elements- toothlike/bladelike structures used to slice and crush food. May have been on a tonguelike structure. Had large eyes/eye muscles for catching prey.
Euagnathans- these fishes lack bone and have a single median nostril (lampreys and hagfishes)
Myxini- the hagfishes. They use teethlike structures on their muscular tongue to scrape flesh from prey. They can knot their bodies for extra force. They lack bone and scales. They have a median nasal opening.
Pteraspidomorphi (Diplorhina)- They have paired nasal openings and bony plates that make up head shields. Their exoskeleton is made of small plates and scales with spines.
Cephalaspidomorpha (Monorhina)- the lampreys. They have a single nasal opening. Their oval mouths are used to maintain position in a current, and cling to prey so their rough tongue can rasp the flesh of prey.
GNATHOSTOMES- fishes with jaws for biting, derived from anterior pharyngeal arches. They also have paired fins. One set, pectoral fins- are anteriorly/laterally placed and the pelvic fins- are posteriorly placed
Placodermi- the placoderms- plates and skin. They were encased in bone with a head shield. They were flattened and benthic.
Chondrichthyes- the cartilage fish. They have endoskeletons of cartilage impregnated with calcium. Teeth are bone but scales and vertebrae have traces (sharks and chimaeras)
Elasmobranchii- sharks and rays. Basking and whale sharks strain food from the water that enters their open mouth with gill bars. Others have teeth. Some rays use gill bars and others teeth foe crushing shellfish.
Holocephali-Chimaeras- the ratfishes. Like sharks except they have opercula (gill covers) and lack scales.
Acanthodii- fish with a row of spines along the top and sides of the body and in the leading edge of all fins except the caudal fin. Have scales, bony plates, but no head shield.
Osteichthyes- bony fishes. They have scales. Their endoskeleton is made of bone. They have a swim bladder- a gas-filled bag that provides neutral buoyancy. Bony fishes are divided into two groups.
Actinopterygii- ray-finned fishes. Their fins are internally supported by numerous slender rays called lepidotrichia. Muscles that control the fins are in the body wall. They are divided into two groups.
Chondrostei- primitive ray-finned fishes. The surviving ones are the paddlefish and the sturgeon. They have a notochord and scales. The endoskeleton was formerly bone but now it is cartilage. They are toothless. Some have an air bladder that is lunglike (they need air). Pectoral fins are fleshy.
Neopterygii- ray-finned fishes. They are the gars and bowfins. They have scales. They have vertebrae.
Sarcopterygii- fleshly-finned fishes. Their fins are fleshly (muscles are outside body wall). They gave rise to amphibians. Their external nostrils open internally to the mouth through holes called choanae. They are divided into two groups.
Dipnoi- the lung fishes. Can breathe when oxygen levels in water fall or when water evaporates.
Crossopterygii- includes the coelacanths. Notochord and vertebrae are present.
TETRAPODS- four-footed (quadrupeds)
Amphibia- contains three major taxa. One taxon contains frogs, salamanders, and caecilians. The other two are known only from fossils.
Labyrinthodontia- ancient amphibians with bony scales in the abdominal region. Some were like four footed fish and had radial fin rays that supported a tail fin. Also had a notochord. Middle ear bones derived from part of the second gill arch. Later limbs began to replace fins and they inherited lungs and aquatic (external) reproduction
Lepospondyli- they had a solid vertebra in which all three elements are fused on to a single, spool-shaped centrum. They were entirely aquatic which reversed the trend.
Lissamphibians- frogs, salamanders, and caecilians. Only frogs have external (aquatic) fertilization, others have internal. Paired lungs are present but may be absent in some salamanders. Many bones of the ancient skull are lost and scales are absent for respiration except in caecilians. They are divided into:
Urodela (Caudata)- the salamanders and newts. Have paired limbs and a long tail. Compared to the ancestral amphibian skull, their skull is more broad and has less bones which were fused or lost. They lack a tympanum (eardrum). In primitive ones fertilization is external but in modern ones it is internal.
Salientia (Anura)- the frogs and toads. Anura means no tail which describes the adult. Salientian means jumpers. A typanum is present and well developed in males that vocalize. Larvae are called
Tadpoles and they scrape algae from rock for food. They metamorphose into adults.
Gymnophiona (Apoda)- the caecilians. They show no trace of limbs and are sometimes called apodians (no feet). Their skull is solid and compact (unlike open skulls of frogs and salamanders).
AMNIOTES- bear embryos enveloped in extraembryonic membranes which, in some, is packaged in a calcareous and leathery shelled egg. Respiration is primarily through the lungs and little through the skin. They are divided into two major groups:
1.Sauropsids- they are divided into the
A. Mesosaurs- had a long snout with teeth used for filter feeding and catching fish. They had paddle-shaped feet, laterally compressed tail, and long neck. Neural arches of the trunk were expanded and overlapping to resist torsion (twisting).
B. Reptilia- divided into two groups:
1.Anapsida- (Testudines or turtles). They have a shell made up of a dorsal carapace- ribs and surface skin plates (scutes) and a connected ventral plastron- fused bony pieces.
2. Diapsida- includes the ichthyosaurs with their porpoise like design, the nothosaurs and plesiosaurs with their long necks and paddle like limbs, the modern squamates (snakes and lizards), the archosauria (crocodiles, birds, flying pterosaurs, dinosaurs) with their bipedalism- two-footed locomotion.
2. Synapsida- These are the mammal like reptiles. They are divided into the:
A. Pelycosauria- they had a broad sail on their backs which was skin supported by neural spines. Might have been used for mating, fighting, or heat collection.
B. Therapsida- They had four legs that were directly under the body, teeth were differentiated into different types, skulls were simple, had hair
1.Cynodonts- some had a horny beak, others had teeth, limbs were under the body, had nose bones that could warm in coming air.
C. Mammalia- They have a pelage (a thick coat of hair) which holds in heat and plays a sensory role such as vibrissae (whiskers) do. They also have sweat glands that are associated with the hair for heat removal and mammary glands for nursing. They can maintain a high body temperature. Their ear consists of three middle ear bones. Their teeth are replaced once in a life time. They include the monotremes (duckbill platypus and Australian anteaters) the marsupials (opossums and kangaroos), and the placentals (animals with a placenta- a vascular organ that connects the fetus to the mother’s uterus).
D. Living organisms come in a great variety of sizes
E.
F. However, not all designs work equally well for all sizes
G.
H. Differences in size necessarily bring differences in performance and design.
I.
J. The study of size and its consequence is known as scaling. Difference sized animals have different physical challenges.
K.
L. Different sized animals also have different metabolic challenges as well.
M.
N. As body size increases, oxygen consumption per unit of body mass decreases.
O.
P. When an object increases in volume, its mass increases proportionately. Bones of large animals are relatively more massive and robust than the bones of small animals.
Q. To remain balanced, an animal must have a shape that can be altered as its length and area and mass grow at different rates.
R. This change in shape in correlation with a change in size is called allometry.
S.
T. Reference feature- a part not being studied
U. Positive allometry- when a feature of study grows faster than the reference feature.
V. Negative allometry- when a feature of study grows slower than the reference feature.
W. Isometry- steady growth that is neither positive or negative allometry.
X.
Y. Body parts used for display or defense, such as adult ram horns, often show allometry.
Z.
AA. As a male lobster grows, its claw shows geometric growth- length is multiplied by a constant per time interval. Its body shows arithmetic growth- a constant is added to its length per time interval.
BB.
CC. Length- a concept of distance
DD. Time- a concept of the flow of events
EE.Mass- a concept of gravity and space
FF. Velocity- the rate of change in an object’s position.
GG. Acceleration- the rate of change in velocity
HH. Force (F)- the mass (m) of an object multiplied by its acceleration (a).
II. In the vertebrates, muscles generate forces and skeletal elements apply these forces. This can be seen with torques and levers.
JJ. Fulcrum- a pivot point between two weights
KK. Lever arm- distance from weight to fulcrum
LL. Short lever arms need more weight to level
MM.
NN. Weight added to a short elbow will cause that arm to move slower with more force than weight added to an even shorter elbow
OO.
PP. Arms that are extended and tapered promote laminar flow (smooth flow) rather than turbulent flow (irregular flow).
FERTILIZATION
Fertilization- the union of two mature gametes (sex cells).
Sperm- the male gamete
Ovum or egg- the female gamete
While in the ovary, the ovum accumulates vitellogenin- a transport form of yolk formed in the liver of the female and carried in her blood.
Once in the ovum, the vitellogenin is transformed into yolk platelets that consist of storage packets of nutrients that help support the growing needs of the developing embryo. The quantity of yolk that collects in the ovum is specific to each species.
Microlecithal- eggs with slight amounts of yolk
Mesolecithal- eggs with moderate amounts of yolk
Macrolecithal- eggs with enormous amounts of yolk
Isolecithal- yolk that is evenly distributed
Telolecithal- yolk that is concentrated at one pole of the spherical ovum
Polarity- when the yolk and other constituents are unevenly arranged
Vegetal pole- where most of the yolk is
Animal pole- where the nucleus is
CLEAVAGE
Blastomeres- the cells resulting from the early cleavage divisions of the ovum.
Holoblastic cleavage- mitotic furrows pass successfully through the entire zygote from animal to vegetal pole.
Meroblastic cleavage- when only a portion of the cytoplasm is cleaved because cell division and mitotic furrowing is slowed due to plentiful yolk in the embryo.
Discoidal cleavage- when cleavage is restricted to a cap of dividing cells at the animal pole because extensive yolk material at the vegetal pole remains undivided by mitotic furrows.
Amphioxus
Eggs are microlecithal. The first cleavage plane passes from animal to vegetal pole, forming two blastomeres. The second cleavage plane is at right angles to the first and also passes from animal to vegetal poles, producing an embryo of four cells. The third cleavage plane is at right angles to the first two and lies between poles just above the equator, producing the eight-celled morula stage.
Fishes
In gars and bowfins, cleavage is holoblastic, although cleavage furrows of the vegetal pole are slowed. Most cell division is restricted to the animal pole. Blastomeres in the vegetal pole are relatively large and hold most of the yolk reserves; those in the animal pole are relatively small and form the blastoderm- a cap of cells arched over a small blastocoel.
In hagfishes, chondrichthyans, and most teleosts, cleavage is strongly discoidal, leaving most of the yolky cytoplasm of the vegetal pole undivided. Cleavage in teleosts produces two cell populations in the blastula.
Amphibians
Blastomeres of the animal pole divide more often than those of the vegetal pole, in which cell division is presumably slowed by abundant yolk platelets. Consequently, cells of the vegetal pole, having undergone fewer divisions, are larger than those of the more active animal pole. When the blastula stage is reached, the small blastomeres of the animal pole constitute the blastoderm and form a roof over the emerging blastocoel.
Reptiles and Birds
Yolk is so prevalent within the vegetal pole that cleavage furrows do not pass through it at all; thus, cleavage is discoidal. Blastomeres resulting from successful cleavage clump at the animal pole, forming the blastoderm (descriptively termed a blastodisc in reptiles and birds) that rests atop the undivided yolk.
Mammals
The blastula stage is termed a blastocyst.
Monotremes
Yolk platelets collect in the ovum to produce a macrolecithal egg. When the ovum is released from the ovary, the follicle cells are left behind. Cleavage, which is discoidal, begins during the passage of the embryo down the oviduct and gives rise to the blastoderm- a cap of cells that rests atop the undivided yolk.
Marsupials
The ovum accumulates only modest amounts of yolk. Early cleavage does not result in formation of a morula.
Placentals
The ovum contains very little yolk when it is released from the ovary. After fertilization, cleavage results in the morula.
GASTRULATION AND NEURULATION
Gastrulation- gut formation, the process by which the embryo (blastula) forms a distinct endodermal tube that is the early gut.
Neurulation- nerve formation, the process of forming an ectodermal tube, the neural tube.
Amphioxus
Gastrulation occurs by invagination of the vegetal wall.
Fishes
In lampreys and primitive bony fishes, the onset of gastrulation is marked by the appearance of an indentation, the dorsal edge of which is the dorsal lip of the blastopore.
In sharks and teleost fishes, during gastrulation, the blastoderm grows over the surface of the yolk, eventually engulfing it completely to form the extraembryonic yolk sac.
Amphibians
A superficial indentation marks the beginning of gastrulation and establishes the dorsal lip of the blastopore.
Reptiles and Birds
The onset of gastrulation is marked in the epiblast by the appearance of a thickened area at what will eventually be the posterior region of the embryo.
Mammals
Monotremes
Gastrulation involves a blastodisc atop a large yolk mass.
Marsupials
During pregastrulation, the unilaminar blastocyst is transformed into a bilaminar embryo with an ectoderm and an endoderm.
Placentals
During pregastrulation, reorganization of the inner cell mass produces a bilaminar embryonic disc composed of epiblast (future ectoderm and mesoderm) and hypoblast (future extraembryonic tissue).
Integument- skin
Epidermis- surface
Dermis- below the epidermis
Basement membrane- between epidermis and dermis
Hypodermis- between the integument and deep body muscular, also called the superficial fascia
GENERAL FEATURES
Dermis
Dermal bones- plates of bone produced by the dermis
Plies- layers of woven collagen fibers
Bias- skin stretches when it is pulled at an angle
Epidermis
Stratum corneum- the epidermis of terrestrial vertebrates that is keratinized or cornified
Keratin- an accumulation of protein products by a process called keratinization.
Callus- a thick protective layer formed by a cornified layer due to friction on the body
Keratinizing system- converts keratinocytes (epidermal cells) into cornified structures
Dermal scale- a fold in the integument that consists mostly of bone
Epidermal scale- a fold in the integument that consists of a keratinized layer
PHYLOGENY
Integument of Fishes
Microridges- hold the surface layer of mucus
Mucous cuticle- mucous coat that blocks bacteria and promotes laminar flow
Club cell- an elongate unicellular gland that releases chemicals to warn others of danger
Granular cell- contributes to the mucous cuticle in lamprey and other fishes
Goblet cell- contributes to the mucous cuticle in bony and cartilage fish
Sacciform cell- holds chemicals that are toxic repellents to be used on enemies
Enamel- a hard scale coating
Primitive Fishes
Thread cells- discharge thick cords of mucus to the skin surface in hagfishes
Slime glands- release their products to the surface via ducts in hagfishes
Chondrichthyes
Placoid scales- surface denticles that give a rough feel to the surface of the skin
Bony Fishes
Cosmoid scale- resides upon a double layer of bone
Ganoid scale- has a thick surface coat of enamel (ganoin)
Teleost scale- lacks enamel and a bone layer
Cycloid scale- a teleost scale composed of concentric rings or circuli.
Ctenoid scale- a teleost scale that has a fringe of projections along posterior margin
Integument of Tetrapods
Amphibians
Cutaneous respiration- respiration through the skin due to the lack of lungs
Leydig cells- large cells thought to secrete substances that stop entry of bacteria/viruses
Nuptial pads- raised calluses that form on digits of males during mating season
Mucous glands- secrete mucous
Poison glands- secrete poison
Reptiles
Hinge- a flexible junction between the epidermal scales
Scute- platelike epidermal scales
Osteoderms- plates of dermal bone located under the epidermal scales for support
Molting or ecdysis- shedding of the cornified layer that removes the epidermis
Scent glands- produce chemicals for social communication in crocodiles and turtles
Birds
Uropygial gland- located at the base of the tail, secretes a lipid and protein product
Salt gland- located on the head of marine birds, excretes excess salt from food
Pterylae- tracts on the surface of the body that contain feathers
Feather follicles- invaginations of the epidermis that dip into the dermis
Feathers- modified scales
Rachis- the central axis of the feather that bears barbs
Calamus- attaches to the body
Mammals
Epidermis may be specialized as hair, glands, or nails.
Dermis is double layered
Papillary layer- the outer dermis layer that pushes dermal papillae into the epidermis
Reticular layer- deeper dermis layer that has fibrous connective tissue for anchoring
Hair- slender keratinous filaments, the base of which is a root and the rest is the shaft.
Cuticle- the scaly outer surface of the shaft
Hair cortex- layer beneath the cortex and above the hair medulla (the hair core).
Hair follicle- where the hair is produced
Arrector pili- smooth muscle attached to the follicle and the dermis which makes stand
Fur or pelage- thick hair composed of guard hairs- large coarse hair on outer fur surface
Underfur- fine and short hair beneath the guard hair
Vibrissae- specialized hair associated with nerves, also called whiskers
Quills- stiff coarse hairs specialized for defense
Sebaceous glands- produce an oily secretion called sebum that is released into follicles
Wax glands- produce wax in the outer ear canal
Meibomian glands- secrete an oily film over the surface of the eyeball
Sweat glands- produce a watery product called perspiration or sweat
Scent glands- produce secretions that play a part in social communication
Mammary glands- function only in females and produce milk- watery mixture of fats, carbohydrates, and proteins for the young
SPECIALIZATIONS
Nails, Claws, Hooves
Nails- plates of tight cornified epithelial cells on the surface of fingers and toes
Claws or talons- curved, laterally compressed keratinized projections from the tips of digits
Hooves- enlarged keratinized plates on the tips of ungulate digits
Horns and Antlers
Horns- a cornified sheath, produced by the integument, that overlies a bony core
Antlers- living skin, called velvet, that overlies and shapes growing bone
Baleen
Baleen- integument within the mouths of some whales that act as strainers
Scales
Scales- folds in the integument
Dermal Armor
Carapace- the dorsal half of turtle shells
Plastron- fused dermal bones along the belly of turtles
Color
Melanophore- a chromatophore that contains the pigment melanin
Melanosomes- cellular organells that house melanin granules that stop harmful radiation
Dermal melanophore- a broad flat cell that changes color rapidly, found in ectotherms
Epidermal melanophore- a thin elongated cell in vertebrates, mostly in endotherms
Iridophore- a chromatophore that contains light-reflecting, crystalline platelets
Erythrophore- a chromatophore that contains red pigments
INTRODUCTION
The vertebrate cranium (skull) is a structure formed of three distinct parts:
1.Splanchnocranium (visceral cranium)-
arose to support pharyngeal slits in protochordates
2. Chondrocranium- underlies and supports
the brain, formed of bone or cartilage
3. Dermatocranium- forms most of the outer casing of the skull of later vertebrates
Braincase- the fused cranial components surrounding and encasing the brain (dermato, chondro, and splanchnocrania)
Neurocranium- the chondrocranium along with fused or attached sensory capsules
CHONDROCRANIUM
Elements of it appear to lie in series with the bases of the vertebrae.
Embryology
Cartilage grows and fuses together to produce the:
1.Ethmoid plate- the region between the
nasal capsule- sensory capsules associated
with the nose
2. Basal plate- between the otic capsules-
sensory capsules associated with ears
3. Occipital arch- cartilage around the nerve cord that later ossify and form basic bones and optic capsules- sensory capsules
associated with eyes
SPLANCHNOCRANIUM
In amphioxus it, or at least its forerunner, is associated with the filter-feeding surfaces.
Among vertebrates, it supports the gills and offers attachment for respiratory muscles. Its elements contribute to jaws and hyoid apparatus of the gnathostomes.
Embryology
It arises from neural crest cells.
In protochordates, neural crest cells are absent. Pharyngeal bars form the branchial basket, the predecessor of the vertebrate splanchnocranium.
In vertebrates, cells of the neural crest depart from the sides of the neural tube and move into the walls of the pharynx between pharyngeal slits to form pharyngeal arches-
branchial/gill arches of aquatic vertebrates
Each arch has 5 elements, dorsal to ventral:
1.the pharyngobranchial element
2.the epibranchial element
3.the ceratobranchial element
4.the hypobranchial element
5.the basibranchial element
One or more anterior branchial arches may: 1. Border the mouth
2. Support soft tissue
3. Bear teeth
Jaws- branchial arches that support the mouth.
Mandibular arch- the largest and most anterior of the modified arches.
This arch is composed of, dorsal to ventral:
1.the palatoquadrate
2.Meckel’s cartilage (mandibular cartilage)
Posterior to the mandibular arch but anterior to the branchial arches is the hyoid arch.
The hyoid arch is composed of the hyomandibula.
Origin of Jaws
Jaws arose from one of the anterior pair of gill arches. Evidence is from these sources:
1.Embryology of sharks suggests that jaws
and branchial arches develop similarly in series and both arise from neural crest
2. Nerves and blood vessels are
Distributed in a pattern similar to branchial arches and jaws
3. The musculature of the jaws appears to be
transformed and modified from branchial arch musculature
The specifics of the above are controversial.
Types of Jaw Attachments
Suspensorium- how the mandible is attached to the skull.
Paleostylic- none of the arches attach themselves directly to the skull (agnathans).
Euautostylic- the mandibular arch is suspended from the skull by itself without help from the hydroid arch (placoderms).
Amphistylic- jaws are attached to the braincase through two articulations:
1.by a ligament connecting the
palatoquadrate to the skull (anteriorly)
2. by the hyomandibula (posteriorly)
[early sharks (most modern ones have a
variation of this), some early bony fish]
Hyostylic- the mandibular arch is attached to the braincase primarily through the hyomandibula. Often a new dermal element, the symplectic bone, aids in jaw suspension (most modern bony fish)
Metautostylic- jaws are attached to the braincase directly through the quadrate- a bone formed in the posterior part of the palatoquadrate (most amphibians, reptiles, and birds).
Craniostylic- the entire upper jaw is incorporated into the braincase but the lower jaw is suspended from the dermal squamosal bone of the braincase (mammals).
In mammals, the splanchnocranium does not contribute to the adult jaws or their suspension.
DERMATOCRANIUM
It consists of dermal bones that form:
1.the sides and roof of the skull to complete the protective bony case around the brain
2.most of the bony lining of the roof of the
mouth
3. much of the splanochnocranium
These bones arise from the bony armor of the integument of early fishes.
Parts of the Dermatocranium
Facial Series
The facial series encircles the external naris and collectively forms the snout
Maxilla and premaxilla- the margin of the snout that has the teeth
Nasal- lies medial to the naris
Septomaxilla- sunken below the surface bones and aids in forming the nasal cavity
Orbital Series
The dermal bones that encircle the eye to define the orbit.
Lacrimal- the ring of bones in front of the orbit where tear ducts are located
Prefrontal, postfrontal, and postorbital- the ring of bones above and behind the orbit
Jugal- the lower rim of the orbit
Temporal Series
Lies behind the orbit and completes the posterior wall of the braincase.
Intertemporal, supratemporal, and tabular- a row of bones that make up the medial part
Squamosal and quadratojugal- bones that form the cheek
Vault Series
The vault (roofing bones) that run across the top of the skull and cover the brain beneath.
Frontal- anterior roof bone
Postparietal (interparietal)- posterior roof bone
Parietal- center roof bone between the frontal and postparietal bones
Palatal Series
Primary palate- bones that cover much of the roof of the mouth
Pterygoid- the largest and most medial bone
Vomer, palatine, and ectopterygoid- bones lateral to the pterygoid that may have teeth
Parasphenoid- an unpaired medial bone present in fishes and lower tetrapods
Mandibular Series
Meckel’s cartilage is usually encased in dermal bone.
Dentary- the lateral wall that has teeth
Angular- the posterior corner of the mandible
Surangular- above the angular
Prearticular and coronoids- make up the mandibular wall
Mandibular symphysis- the midline where left and right mandibles meet anteriorly
PHYLOGENY OF THE SKULL
Agnathans
Ostracoderms
Eyes: two, close-set, dorsally placed
Pineal opening: single, between eyes
Nostril: in front of the pineal opening
They had a single bony shield covering the head
Sequential branchial arches stretched like beams across the roof of the pharynx
Ostracoderms-Anaspids
Eyes: lateral,
Pineal opening: between eyes
Nostril: single, in front of pineal opening
Many small bony scales covered the head
Ostracoderms-Heterostracans
Eyes: small, laterally placed
Pineal opening: median
Nostril: not median, not present
Head was made of several fused bony plates
Cyclostomes
They lack bone entirely
Cyclostomes-Lampreys
Pineal opening: single
Nostril: single, median
Branchial arches form an unjointed branchial basket
Cyclostomes-Hagfishes
Pineal opening: not external
Nostril: median
Gnathostomes
Fishes
Fishes-Placoderms
Had a cranial shield- dermal plates of the head that were thick and tightly joined.
The braincase was heavily ossified and the upper jaws were attached to it.
Fishes-Acathodians
Some had an operculum- a bony flap that covered the exit gill slits
The mandibular arch was much like that of sharks and bony fishes. A hyoid arch and 5 successive branchial arches were present.
Fishes-Chondrichthyans
They have almost no bone
A dematocranium is absent
In primitive chondrichthyans, six gill arches trailed the mandibles. The upper jaw (palatoquadrate) of primitive sharks was supported by the braincase and probably by the hyomandibula.
In modern sharks, there is not a strong, direct attachment between hyomandibula and palatoquadrate. Instead, the jaws are suspended at two other sites.
Fishes-Actinopterygians
Early ones had long jaws that extended to the front of the head. The jaws carried numerous teeth and an operculum covered the gill arches. The hyoid arch increased its support of the mandibles.
In primitive ones the suspensorium is formed from the fusion of various bones that includes the hyomandibula, the palatine, and the quadrate. The suspensorium is shaped like an inverted triangle.
In advanced ones (like the teleosts) the neurocranium is raised and the mandible is lowered during jaw opening. The hyoid apparatus aids in suction.
Fishes-Sarcopterygians
In early lungfishes the upper jaw (palatoquadrate) was fused to the braincase.
Amphibians
In the early ones the hyomandibula ceases to be involved in jaw suspension and instead becomes dedicated to hearing as the columella (or stapes) within the middle ear. The opercular series of bones are lost.
They had a dermatocranium
In modern ones the jaw suspension is by the articular and quadrate bones through which the mandible articulates with the skull. The branchial arches are in the larvae are reduced to the hyoid apparatus in adults.
The splanocranium which is prominent in fish is reduced
Primitive Reptiles
The palatoquadrate of the mandibular arch was reduced to the small epipterygoid and separate quadrate. The hyoid arch produced the columella (stapes).
Modern Reptiles
There is no significant mobility in the in the dermatocranium so the mandible slides back and forth on the fixed quadrate from which it is suspended.
Birds
The palatal bones are reduced and lightened.
Vomers and ectopterygoids are small, pterygoids are short struts articulating with the quadrate, and epipterygoids are usually lost. The jaws are drawn out into a beak.
The upper temporal bar is absent, and the lower temporal bar is a slender rod called the jugal bar (quadratojugal-jugal bar), which extends from the beak posteriorly to the side of the movable (streptostylic) quadrate.
Synapsids
Primitive Synapsids
In the early ones, the temporal region developed an opening under which was the jugal and the squamosal bones.
In advanced ones and primitive mammals, the connection between the jugal and squamosal bones forms the cheek region
Mammals
Various dermal elements are lost in therian mammals including the septomaxilla, prefrontal, postorbital, postfrontal, quadratojugal, and supratemporal bones.
Monotremes retain several reptilian skull features, including prefrontal, and postfrontal bones
Placental Mammals
On the side of the brain case behind the orbit, a large temporal bone is formed by the fusion of contributions from all three parts of the skull
THE APPENDICULAR SKELETON
BASIC COMPONENTS
Appendicular skeleton- the fins or limbs and the girdles- the braces within the body that support the fins or limbs
Anterior girdle- the shoulder or pectoral girdle that support the pectoral fin or limb
Posterior girdle- the hip or pelvic girdle that support the pelvic fin or limb
Fins
Fins- membranous or webbed processes internally strengthened by radiating and thin dermal fin rays
Ceratotrichia- dermal fin rays in elasmobranchs
Lepidotrichia- dermal fin rays in bony fishes
Actinotrichia- keratinized rods that stiffen the fin tips of some bony fishes
Pterygiophores- supports the proximal part of the fin close to the body. There are two types:
1.Basals- in the proximal part of the fin
2.Radials- in the middle part of the fin
(Basals and radials are connected)
Fins occur singly, except for the pectoral fins (near the head) and the pelvic fins (posterior to pectoral fins).
These paired fins, pectoral and pelvic fins, receive attention because they are the phylogenetic source of the tetrapod limbs.
Limbs
The forelimbs and hindlimbs of tetrapods are composed of three regions:
1.Autopodium- the distal end of the limb
2. Zeugopodium- the middle region
3. Stylopodium- the region near the body
PHYLOGENY
Fishes
Agnathans
Ostracoderms had unpaired medial fins, a caudal fin on the tail, and often unpaired anal and dorsal fins. Most lacked paired pectoral fins. All lacked pelvic fins.
Some anaspids had long lateral fin folds running the length of their bodies.
Heterostraci and Galeaspida fossils lacked traces of paired fins
Living cyclostomes clearly lack paired fins
Only among some osteostracans were paired fins present and only in the pectoral region
Placoderms
Both pectoral and pelvic girdles were present.
Chondrichthyans
Primitive ones had pectoral and pelvic fins. They consisted of basal elements and tightly packed radials supporting the fin.
In later ones, the paired basal components of the pectoral and pelvic girdles became extended across the midline of the body to fuse into U-shaped:
Scapulocoracoid bars- fused basal components of pectoral girdles
Pubioischiac bars- fused basal components of pelvic girdles
Acanthodians
They had large spines that formed the leading edge of dorsal, anal, and paired fins. In some, the pectoral spine articulated with a girdle but the pelvic spine did not.
Bony Fishes
In actinopterygians the dermal shoulder girdle forms a U-shaped collar of bone around the posterior border of the gill chamber.
The sarcopterygians have muscles that project from the body to form the fleshy base of the fin.
The primitive ones had fin features that gave rise to the limb features of early tetrapods.
Surviving sarcopterygians such as the lungfish have reduced fins that are unsuited for land.
Surviving crossopterygians such as the coelacanth have fins that are unsuited for land as well
The pectoral and pelvic appendages of fossil rhipidistians had bones homologous to bones of early tetrapod limbs. The pectoral and pelvic fins articulated with girdle bone.
Tetrapods
In early amphibians, such as Ichthyostega, the girdles and limbs became stronger. The pectoral girdle lost its attachment to the skull. The fins were replaced by digits.
Aerial Locomotion
“Flying” fish spread especially wide pectoral fins during short flights above water
A species of tropical frog spreads its long, webbed toes to slow its airborne fall
Lizards with special flaps of skin and squirrels with loose skin between fore- and hindlimbs spread these membranes to slow their drop through the air or to extend the distance of their horizontal travel
All of these tentative fliers are not really fliers at all. They are gliders and parachutists.
True power flight occurs in just three groups:
1.bats
2.pterosaurs
3.most birds
In each group above, the forelimbs are modified into wings that both generate the force driving them forward through the air and provide lift against gravity.
CHAPTER 14
Vertebrate Beginnings: The Chordates
Page 269, column 1, paragraph 1:
Animals most familiar to people belong to the phylum Chordata. Humans are members and share the characteristic from which the phylum derives its name-the notochord.
Four Chordate Hallmarks
Page 270, column 2, paragraph 1:
The four distinctive characteristics that, taken together, set chordates apart from all other phyla are the notochord; single, dorsal, tubular nerve cord; pharyngeal pouches; and postanal tail.
These characteristics are always found at some embryonic stage, although they may be altered or may disappear altogether in later stages of the life cycle.
Notochord
Page 273, column 1, paragraph 1:
The notochord is a flexible, rodlike structure, extending the length of the body; it is the first part of the endoskeleton to appear in the embryo.
The notochord is an axis for muscle attachment, and because it can bend without shortening, it permits undulatory movements of the body.
In most protochordates and in jawless vertebrates, the notochord persists throughout life.
In all jawed vertebrates a series of cartilaginous or bony vertebrae is formed from the connective tissue sheath around the notochord and replaces the notochord as the chief mechanical axis of the body.
Dorsal, Tubular Nerve Cord
Page 273, column 1, paragraph 2:
In most invertebrate phyla that have a nerve cord, it is ventral to the alimentary canal and is solid, but in the chordates the single cord is dorsal to the alimentary canal and notochord and is a tube (although the hollow center may be nearly obliterated during growth).
In vertebrates the anterior end becomes enlarged to form the brain. The hollow cord is produced in the embryo by the infolding of the ectodermal cells on the dorsal side of the body above the notochord.
The nerve cord passes through the protective neural arches of the vertebrae, and the anterior brain is surrounded by a bony or cartilaginous cranium.
Pharyngeal Pouches and Slits
Page 273, column 2, paragraph 1:
Pharyngeal slits are perforated slitlike openings that lead from the pharyngeal cavity to the outside.
They are formed by the inpocketing of the outside ectoderm (pharyngeal grooves) and the evagination, or outpocketing, of the endodermal lining of the pharynx (pharyngeal pouches).
In aquatic chordates, the two pockets break through the pharyngeal cavity where they meet to form the pharyngeal slit.
In amniotes these pockets may not break through the pharyngeal cavity and only grooves are formed instead of slits.
In tetrapod vertebrates the pharyngeal pouches give rise to several different structures, including Eustachian tube, middle ear cavity, tonsils, and parathyroid glands.
Page 273, column 2, paragraph 2:
The perforated pharynx evolved as a filter-feeding apparatus and is used as such in the protochordates.
Water with suspended food particles is drawn by ciliary action through the mouth and flows out through the pharyngeal slits, where food is trapped in mucus.
In the vertebrates, ciliary action is replaced by a muscular pump that drives water through the pharynx by expanding and contracting the pharyngeal cavity.
Also modified are the blood vessels that carry blood through the pharyngeal bars. In prorchordates these are simple vessels surrounded by connective tissue.
In the early fishes a capillary network was added with only thin, gas-permeable walls separating water outside from blood inside.
This improved efficiency of gas transfer. These adaptations led to the development of internal gills, completing the conversion of the pharynx from a filter-feeding apparatus in protochordates to a respiratory organ in aquatic vertebrates.
Postanal Tail
Page 274, column 1, paragraph 1:
The postanal tail, together with somatic musculature and the stiffened notochord, provides the motility that larval tunicates and amphioxus need for their free-swimming existence.
As a structure added to the body behind the anus, it clearly has evolved specifically for propulsion in water. Its efficiency is later increased in fishes with the addition of fins.
The tail is evident in humans only as as a vestige (the coccyx, a series of small vertebrae at the end of the spinal column) but most other mammals have a waggable tail as adults.
Subphylum Urochordata (Tunicata)
Page 274, column 2, paragraph 2:
The urochordates (“tail-chordates”), more commonly called tunicates, number some 3000 species.
They are found in all seas from near the shoreline to great depths. Most of them are sessile as adults, although some are free living.
The name “tunicate” is suggested by the usually tough, nonliving tunic, or test, that surrounds the animal.
As adults, tunicates are highly specialized chordates, for in most species only the larval form, which resembles a microscopic tadpole, bears all the chordate hallmarks.
During adult metamorphosis, the notochord (which, in the larva, is restricted to the tail, hence the group name Urochordata) and the tail disappear altogether, while the dorsal nerve cord becomes reduced to a single ganglion.
Page 275, column 1, paragraph 1:
Urochordata is divided into three classes-Ascidiacea, Larvacea, and Thaliacea.
Of these, the members of Ascidiacea, commonly known as the ascidians, or sea squirts, are by far the most common and are the best known.
Page 275, column 1, paragraph 2:
The typical solitary ascidian is a spherical or cylindrical form that is attached by its base to hard substrates such as rocks, pilings, or the bottoms of ships.
Lining the tunic is an inner membrane, the mantle.
On the outside are two projections: the incurrent and excurrent siphons. Water enters the incurrent siphon and passes into the branchial sac (pharynx) through the mouth.
On the midventral side of the branchial sac is a groove, the endostyle, which is ciliated and secretes mucus.
As the mucous sheet is carried by cilia across the inner surface of the pharynx to the dorsal side, it sieves small food particles from the water passing through the slits in the wall of the branchial sac.
Then mucus with its entrapped food is collected and passed posteriorly to the esophagus.
The water, now largely cleared of food particles, is driven by cilia into the atrial cavity and finally out the excurrent siphon. The intestine leads to the anus near the excurrent siphon.
Page 275, column 1, paragraph 3:
The nervous system is restricted to a nerve ganglion and a few nerves that lie on the dorsal side of the pharynx. A notochord is lacking.
Page 275, column 2, paragraph 1:
Of the four chief characteristics of chordates, adult sea squirts have only one, the pharyngeal gill slits.
However, the larval form gives away the secret of their true relationship.
The tiny tadpole larva is an elongate, transparent form with a head and all four chordate characteristics: a notochord, hollow dorsal nerve cord, propulsive postanal tail, and a large pharynx with endostyle and gill slits.
The larva does not feed but swims for several hours before fastening itself vertically by its adhesive papillae to some solid object. It then metamorphoses to become the sessile adult.
Page 275, column 2, paragraph 2:
The remaining two classes of the Urochordata- Larvacea and Thaliacea-are mostly small, transparent animals of the open sea.
Some are small, tadpolelike forms resembling the larval stage of ascidians. Others are spindle shaped or cylindrical forms surrounded by delicate muscle bands.
They are mostly carried along by the ocean currents and as such form a part of the plankton.
Many are provioded with luminous organs and emit a beautiful light at night.
Subphylum Cephalochordata
Page 275, column 2, paragraph 3:
The cephalochordates are the marine lancelets: slender, laterally compressed, translucent animals about 5 to 7 cm in length that inhabit the sandy bottoms of coastal waters around the world.
Lancelets orginally bore the generic name Amphioxus, later surrendered by priority to Branchiostoma.
Amphioxus is stillused, however, as a convenient common name for all of the approximate 26 species in this diminutive subphylum. Four species of amphioxus (lancelets) are found in North American coastal waters.
Page 276, column 2, paragraph 1:
Amphioxus is especially interesting because it has the four distinctive characteristics of chordates in simple form.
Water enters the mouth, driven by cilia in the buccal cavity, and then passes through numerous pharyngeal slits in the pharynx, where food is trapped in mucus, which is then moved by cilia into the intestine.
Here the smallest food particles are separated from the mucus and passed into the midgut caecum (diverticulum), where they are phagocytized and digested intracellularly.
As in tunicates, the filtered water passes first into an atrium, and then leaves the body by an atriopore (equivalent to the excurrent siphon of tunicates).
Page 276, column 2, paragraph 3:
The nervous system is centered around a hollow nerve cord lying above the notochord.
Sense organs are simple, unpaired bipolar receptors located in various parts of the body. The “brain” is a simple vesicle at the anterior end of the nerve cord.
Page 277, column 1, paragraph 1:
No other chordate shows the basic diagnostic characteristics of the chordates so well.
In addition to the four chordate anatomical hallmarks, amphioxus possess several structural features that foreshadow the vertebrate plan.
Among these are the midgut diverticulum, which secretes digestive enzymes, segmented trunk musculature, and the basic circulatory pattern of more advanced chordates.
Subphylum Vertebrata
Page 277, column 1, paragraph 2:
The third subphylum of the chordates is the large and diverse Vertebrata, the subject of the next five chapters of this book.
This group shares the basic chordate characteristics with the other two subphyla, but in addition it reveals a number of novel homologies that the others do not share.
The alternative name of the subphylum, Craniata, more accurately describes the group since all have a cranium (bony or cartilaginous braincase) whereas the jawless fishes lack vertebrae.
CHAPTER 15
Fishes
What Is a Fish?
Page 286, column 1, paragraph 1:
Today we recognize a fish as a gill-breathing, ectothermic, aquatic vertebrate that possesses fins, and a skin that is usually covered with scales.
Superclass Agnatha: Jawless Fishes
Page 287, column 2, paragraph 2:
The living jawless fishes are represented by approximately 84 species almost equally divided between two classes:
Myxini (hagfishes) and Cephalaspidomorphi (lampreys).
Members of both groups lack jaws, internal ossification, scales, and paired fins, and both groups share porelike gill openings and an eel-like body form.
In other respects, however, the two groups are morphologically very different.
Lamprey bear many derived morphological characteristics that place them phylogenetically much closer to the jawed bony fishes than to the hagfishes.
Because of these differences, hagfishes and lampreys have been assigned to separate vertebrate classes, leaving the grouping “Agnatha” as a phylogenetic assemblage of jawless fishes.
Hagfishes: Class Myxini
Page 287, column 2, paragraph 3:
The hagfishes are an entirely marine group that feed on dead or dying fishes, molluscs, and crustaceans.
They are neither parasitic like lampreys nor predaceous, but are scavengers.
There are only 43 species of hagfishes, of which the best known in North America are the Atlantic hagfish Myxine glutinosa and the Pacific hagfish Eptatretus stouti.
Although almost completely blind, the hagfish is quickly attracted to food, especially dead or dying fish, by its keenly developed senses of smell and touch.
Page 289, column 1, paragraph 0:
After attaching itself to its prey by means of toothed plates, the hagfish thrusts the tongue forward to rasp off pieces of tissue.
For extra leverage, the hagfish often ties a knot in its tail, then passes it forward along the body until it is pressed securely against the side of its prey.
Lampreys: Class Cephalaspidomorphi
Page 291, column 1, paragraph 1:
Of the 41 described species of lampreys distributed around the world, by far the best known to North Americans is the destructive marine lamprey, Petromyzon marinus, of the Great Lakes.
Page 291, column 1, paragraph 6:
The invasion of the Great Lakes above Lake Ontario by the landlocked sea lamprey, Petromyzon marinus, in this century has a devastating effect on the fisheries.
Sea lampreys, accompanied by overfishing, caused the total collapse of a multimillion dollar lake trout fishery in the early 1950s.
Other less valuable fish species were attacked and destroyed in turn.
After reaching a peak abundance in 1951 in Lakes Huron and Michigan and in 1961 in Lake Superior, the sea lampreys began to decline, due in part to depletion of their food and in part to the effectiveness of control measures (mainly chemical larvicides placed in selected spawning streams).
Cartilaginous Fishes: Class Chondrichthyes
Page 291, column 2, paragraph 1:
There are more than 850 living species in the class Chondrichthyes, an ancient, compact, and highly developed group.
Although a much smaller and less diverse assemblage than the bony fishes, their impressive combination of well-developed sense organs, powerful jaws and swimming musculature, and predaceous habits ensures them a secure and lasting niche in the aquatic community.
Page 292, column 1, paragraph 0:
One of their distinctive features is their cartilaginous skeleton.
Although there is some limited calcification, bone is entirely absent throughout the class-a curious feature, since the Chondrichthyes are derived from ancestors having well-developed bone.
Sharks and Rays: Subclass Elasmobranchii
Page 292, column 1, paragraph 1:
Sharks, which make up about 45% of the approximately 815 species in the subclass Elasmobranchii, are typically predaceous fishes with five to seven gill slits on each side and (usually) a spiracle behind each eye.
More than half of all elasmobranchs are rays, specialized for a bottom-feeding life-style.
Unlike sharks, which swim with thrusts of the tail, rays propel themselves by wave-like motions of the “wings,” or pectoral fins.
Page 292, column 2, paragraph 1:
Although to most people sharks have a sinister appearance and a fearsome reputation, they are at the same time among the most gracefully streamlines of all fishes.
Sharks are heavier than water and will sink if not swimming forward.
The asymmetrical heterocercal tail, in which the vertebral column turns upward and extends into the dorsal lobe of the tail, provides lift and thrust as it sweeps to and fro in the water, and the broad head and flat pectoral fins act as planes to provide head lift.
Page 292, column 2, paragraph 2:
Sharks are well equipped for their predatory life.
The tough leathery skin is covered with numerous dermal placoid scales that are modified anteriorly to form replaceable rows of teeth in both jaws.
Page 293, column 1, paragraph 0:
Vision is less acute than in most bony fishes, but a well-developed lateral line system is used for detecting and locating objects and moving animals (predators, prey, and social partners).
It is composed of a canal system extending along the side of the body and over the head.
Inside are special receptor organs (neuromasts) that are extremely sensitive to vibrations and currents in the water.
Sharks can also detect and aim attacks at prey buried in the sand by sensing the bioelectric fields that surround all animals.
The receptors, the ampullary organs of Lorenzini, are located on the shark’s head.
Page 293, column 2, paragraph 1:
Rays belong to a separate order from the sharks.
Rays are distinguished by their dorsoventrally flattened bodies and the much-enlarged pectoral fins that behave as wings in swimming.
The gill openings are on the underside of the head, and the spiracles (on top of the head) are unusually large.
Respiratory water enters through these spiracles to prevent clogging the gills, because the mouth s often buried in sand.
The teeth are adapted for crushing the prey-mainly molluscs, crustaceans, and an occasional small fish.
Page 294, column 1, paragraph 1:
In the stingray, the caudal and dorsal fins have disappeared, and the tail is slender and whiplike.
The stingray tail is armed with one or more saw-toothed spines that can inflict dangerous wounds.
Electric rays have certain dorsal muscles modified into powerful electric organs, which can give severe shocks to stun their prey.
Chimaeras: Subclass Holocephali
Page 294, column 2, paragraph 1:
The approximately 30 species of chimaeras, distinguished by such suggestive names as ratfish, rabbitfish, spookfish, and ghostfish.
Anatomically they present an odd mixture of sharklike and bony fishlike features.
Their food is a mixed diet of seaweed, molluscs, echinoderms, crustaceans, and fishes.
Chimaeras are not commercial species and are seldom caught.
Bony Fishes: Class Osteichthyes
Origin, Evolution, and Diversity
Page 295, column 1, paragraph 1:
The bony fishes are the largest and most diverse taxon of all vertebrates.
Bony fishes developed several key adaptations adaptations that contributed to an extensive adaptive radiation.
An operculum over the gill slits, composed of bony plates attached to the first gill arch, served to increase the efficiency of drawing water across the gill surfaces.
These earliest bony fishes also had a pair of lungs, which served as accessory breathing structures.
The fin pattern established at that time persists in bony fishes today: pectoral and pelvic fins supported by bony girdles embedded in the body musculature, and median dorsal and anal fins.
Progressive specialization of jaw structure and feeding mechanisms is another key feature in bony fish evolution.
Bony fishes have high levels of activity, supported by efficient gill design for gas exchange, rapid metabolic oxidation of food, and an effective form of undulatory locomotion that persisted in many tetrapods (for example, salamanders, snakes, and many lizards).
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Osteichthyes is divided into two distinct lineages.
One lineage, the ray-finned fishes (Actinopterygii), includes the modern bony fishes, the largest of all vertebrate radiations.
The other lineage is the fleshly-finned fishes (Sarcopterygii), a remnant group represented today by the lungfishes and the coelacanth.
Their evolutionary history is of great interest because their descendents include all the land vertebrates (tetrapods).
Ray-Finned Fishes: Subclass Actinopterygii
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Ray-finned fishes are an enormous assemblage containing all of our familiar bony fishes-more than 24,600 species.
The ancestral forms were small, bony fishes, heavily armored with ganoid scales, and had functional lungs as well as gills.
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From these earliest ray-finned fishes, two major groups emerged.
Those bearing the most primitive characteristics are the chondrosteans, represented today by the sturgeons, paddlefishes, and bichir Polypterus of African rivers.
Polypterus is an interesting relic with a lunglike swim bladder and many other primitive characteristics; it resembles an ancestral ray-finned fish more than it does any other living descendant.
There is no satisfactory explanation for the survival to the present of this fish and the coelacanth Latimeria when all of their kin perished millions of years ago.
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The second major group to emerge from the early ray-finned stock were neopterygians.
One lineage gave rise to a secondary radiation that led to the modern bony fishes, the teleosts.
The two surviving genera of the nonteleost neopterygians are the bowfin Amia of shallow, weedy waters of the Great Lakes and Mississippi Valley, and the gars Lepisosteus of eastern and southern North America.
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The major lineage of neopterygians are the teleosts, the modern bony fishes.
The heavy armorlike scales of the early ray-finned fishes have been replaced in teleosts by light, thin, and flexible cycloid and ctenoid scales.
These look much alike except that ctenoid scales have comblike ridges on the exposed edge that may be an adaptation for reducing frictional drag.
Some teleosts, such as some catfishes and sculpins, lack scales altogether.
Nearly all teleosts have a homocercal tail, with the upper and lower lobes of about equal size.
The lungs of early forms were transformed in the teleosts to a swim bladder with a buoyancy function.
Teleosts have highly maneuverable fins for control of body movement.
In small teleosts the fins are often provided with stout, sharp spines, thus making themselves prickly mouthfuls for would-be predators.
With these adaptations (and many others), teleosts have become the most diverse of fishes.
The Fleshy-Finned Fishes:
Subclass Sarcopterygii
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The fleshy-finned fishes are today represented by only seven species: six species (three genera) of lungfishes and a single lobe-finned fish, the coelacanth.
All of the early sarcopterygians had lungs as well as gills and strong, fleshy, paired lobed fins (pectoral and pelvic) that may have been used like four legs to scuttle along the bottom.
They had powerful jaws, a skin covered with heavy, enameled scales, and a diphycercal tail.
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Of the surviving lungfishes, the least specialized is Neoceratodus, the living Australian lungfish, which may attain a length of 1.5 m.
This lungfish is able to survive in stagnant, oxygen-poor water by coming to the surface and gulping air into its single lung, but it cannot live out of water.
The South American lungfish, Lepidosiren, and the African lungfish, Protopterus, can live out of water for long periods of time.
Protopterus lives in African streams and rivers tat run completely dry during the dry season, with their mud beds baked hard by the hot tropical sun.
The fish burrows down at the approach of the dry season and secretes a copious slime that mixes with mud to form a hard cocoon in which it remains dormant until the rains return.
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The lobe-finned fishes consist of two groups: the rhipidistians which became extinct; and the coelacanth, a group that also radiated and later disappeared except for one remarkable species, the famous coelacanth Latimeria chalumnae.
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The fleshy-finned fishes occupy an important position in vertebrate evolution because they include the closest living relatives of the tetrapods.
Of the living flesh-finned fishes, the lungfishes are the sister group of the tetrapods.
CHAPTER 16
The Early Tetrapods and Modern Amphibians
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Adaptation for life on land is a major theme of the remaining vertebrate groups treated in this and the following chapters.
These animals form a monophyletic unit known as the tetrapods.
The amphibians and the amniotes (including reptiles, birds, and mammals) represent the two major extant branches of tetrapod phylogeny.
In this chapter, we review what is known about the origins of terrestrial vertebrates and discuss the amphibian lineage in detail.
Early Evolution of Terrestrial Vertebrates
Devonian Origin of the Tetrapods
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The Devonian period, beginning some 400 million years ago, was a time of mild temperatures and alternating droughts and floods.
During this period some primarily aquatic vertebrates evolved two features that would be important for permitting the subsequent evolution for life on land: lungs and limbs.
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The Devonian freshwater environment was unstable. During dry periods, many pools and streams evaporated, water became foul, and the dissolved oxygen disappeared.
Only those fishes able to acquire atmospheric oxygen survived such conditions.
Gills were unsuitable because in air the filaments collapsed, dried, and quickly lost their function.
Virtually all freshwater fishes surviving this period, including the lobe-finned (rhipidistian) fishes and the lungfishes, had a kind of lung that developed as an outgrowth of the pharynx.
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Vertebrate limbs also arose during the Devonian period.
Although fish fins at first appear very different from the jointed limbs of tetrapods, an examination of the bony elements of the paired fins of the lobe-finned fishes shows that they broadly resemble the equivalent limbs of amphibians.
In Eusthenopteron, a Devonian lobe-fin, we can recognize an upper arm bone (humerus) and two forearm bones (radius and ulna) as well as other elements that we can homologize with the wrist bones of tetrapods.
Eusthenopteron could walk-more accurately flop-along the bottom mud of pools with its fins, since backward and forward movement of the fins was limited to about 20-25 degrees.
Acanthostega, one of the earliest known Devonian tetrapods, had well-formed tetrapod legs with clearly formed digits on both fore-and hindlimbs, but the limbs were too weakly constructed to enable the animal to hoist its body off the surface for proper walking on land.
Ichthyostega, however, with its fully developed shoulder girdle, bulky limb bones, well-developed muscles, and other adaptations for terrestrial life, must have been able to pull itself onto land, although it probably did not walk very well.
Thus, the tetrapods evolved their legs underwater and only then, for reasons unknown, began to pull themselves onto land.
Page 313, column 1, paragraph 1:
Both the lobe-finned fishes and early tetrapods such as Acanthostega and Ichthyostega shared several characteristics of skull, teeth, and pectoral girdle.
Ichthyostega represents an early offshoot of tetrapods phylogeny that possessed several adaptations, in addition to jointed limbs, that equipped it for life on land.
These include a stronger backbone and associated muscles to support the body in air, new muscles to elevate the head, strengthened shoulder and hip girdles, a protective rib cage, a more advanced ear structure for detecting airborne sounds, a foreshortening of the skull, and a lengthening of the snout that improved olfactory powers for detecting dilute airborne odors.
Yet Ichthyostega still resembled aquatic forms in retaining a tail complete with fin rays and in having opercular (gill) bones.
Carboniferous Radiation of the Tetrapods
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The capricious Devonian period was followed by the Carboniferous period, characterized by a warm, wet climate during which mosses and large ferns grew in profusion on a swampy landscape.
Tetrapods radiated quickly in this environment to produce a great variety of forms, feeding on the abundance of insects, insect larvae, and aquatic invertebrates available.
Several extinct lineages plus the Lissamphibia, which contains the modern amphibians, are placed in a group termed the temnospondyls.
This group is distinguished by having generally only four digits on the forelimb rather than the five characteristic of most tetrapods.
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The lissamphibians diversified during the Carboniferous to produce the ancestors of the three major groups of amphibians alive today, frogs (Anura or Salienta), salamanders (Caudata or Urodela), and caecilians (Apoda or Gymnophiona).
The Modern Amphibians
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The three living amphibians orders comprise more than 3900 species.
Most share general adaptation for life on land, including skeletal strengthening and a shifting of special sense priorities from the ancestral lateral line system to the senses of smell and hearing.
For this, both the olfactory epithelium and the ear are redesigned to improve sensitivities to airborne odors and sounds.
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Nonetheless, most amphibians meet the problems of independent life on land only halfway.
In the ancestral life history of amphibians, eggs are aquatic and hatch to produce an aquatic larval form that uses gills for breathing.
A metamorphosis follows in which gills are lost and lungs, which are present throughout larval life, are then activated for respiration.
Many amphibians retain this general pattern but there are some important exceptions.
Some salamanders lack a complete metamorphosis and retain a permanently aquatic, larval morphology throughout life.
Others live entirely on land and lack the aquatic larval phase completely.
Both of these are evolutionarily derived conditions.
Some frogs also have acquired a strictly terrestrial existence by eliminating the aquatic larval stage.
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Even the most terrestrial amphibians remain dependent on very moist if not aquatic environments.
Their skin is thin, and it requires moisture for protection against desiccation in air. An intact frog loses water nearly as rapidly as a skinless frog.
Amphibians also require moderately cool environments.
Being ectothermic, their body temperature is determined by and varies with the environment, greatly restricting where they can live.
This restriction is especially important for reproduction. Eggs are not well protected from desiccation, and they must be shed directly into the water or onto moist terrestrial surfaces.
Completely terrestrial amphibians may lay eggs under logs or rocks, in the moist forest floor, in flooded tree holes, in pockets on the mother’s back, or in folds of the body wall.
One species of Australian frog even broods its young in its vocal pouch.
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We now highlight the special characteristics of the three major groups of amphibians.
Caecilians: Order Gymnophiona (Apoda)
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The order Gymnophiona contains approximately 160 species of elongate, limbless, burrowing creatures commonly called caecilians.
They occur in tropical forests of South America (their principle home), Africa, and Southeast Asia.
They possess a long, slender body, small scales in the skin of some, many vertebrate, long ribs, no limbs, and a terminal anus.
The eyes are small, and most species are totally blind as adults.
Their food consists mostly of worms and small invertebrates, which they find underground.
Fertilization is internal, and the male is provided with a protrusible copulatory organ.
The eggs are usually deposited in moist ground near the water. In some species the eggs are carefully guarded in folds of the body during their development (oviparity).
Viviparity also is common in some caecilians, with the embryos obtaining nourishment by eating the wall of the oviduct.
Salamanders: Order Caudata (Urodela)
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As its name suggests, the order Caudata are tailed amphibians, some 360 species of salamanders.
Salamanders are found in almost all northern temperate regions of the world, and they have great abundance and diversity in North America.
Salamanders are found also in the tropical areas of Central and northern South America.
Salamanders are typically small; most of the common North American salamanders are less than 15 cm long.
Some aquatic forms are considerably longer, and the Japanese giant salamander may exceed 1.5 m in length.
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Most salamanders have limbs set at right angles to the body, with forelimbs and hindlimbs of approximately equal size.
In some aquatic and burrowing forms, the limbs are rudimentary or absent.
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Salamanders are carnivorous both as larvae and adults, preying on worms, small arthropods, and small molluscs.
Most eat only things that are moving. Like all amphibians, they are ectotherms and have a low metabolic rate.
Breeding Behavior
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Some salamanders are wholly aquatic throughout their life cycle, but most are metamorphic, having aquatic larvae and terrestrial adults that live in moist places under stones and rotten logs.
The eggs of most salamanders are fertilized internally, usually after the female picks up a packet of sperm (spermatophore) that previously has been deposited by the male on a leaf or stick.
Aquatic species lay their eggs in clusters or stringy masses in the water.
Their eggs hatch to produce an aquatic larva having external gills and a finlike tail.
Completely terrestrial species deposit eggs in small, grapelike clusters under logs or in excavations in soft moist earth, and many species remain to guard the eggs.
These species have direct development. They bypass the larval stage and hatch as miniature versions of their parents.
The most complex of salamander life cycles is observed in some American newts, whose aquatic larvae metamorphose to form terrestrial juveniles that later metamorphose again to produce secondarily aquatic, breeding adults.
Respiration
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At various stages of their life history, salamanders may have external gills, lungs, both, or neither of these.
They also share the general amphibian condition of having extensive vascular nets in their skin that serve the respiratory exchange of oxygen and carbon dioxide.
Salamanders that have an aquatic larval stage hatch with gills, but lose them later if a metamorphosis occurs.
Several diverse lineages of salamanders have evolved permanently aquatic forms that fail to undergo a complete metamorphosis and retain their gills and finlike tail throughout life.
Lungs, the most widespread respiratory organ of terrestrial vertebrates, are present from birth in the salamanders that have them, and become active following metamorphosis.
Others, such as amphiumas, while having a completely aquatic life history, nonetheless lose their gills before adulthood and then breathe primarily by lungs.
This requires that they periodically raise their nostrils above the surface of the water to get air.
Paedomorphosis
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Whereas most salamanders complete their development by metamorphosis to the adult body form, some species reach sexual maturity while retaining their gills, aquatic life-style, and other larval characteristics.
This condition illustrates paedomorphosis, defined as the retention in adult descendants of features that were present only in the pre-adult stages of their ancestors.
Some adult characteristics of the ancestral adult morphology are consequently eliminated.
Examples of such nonmetamorphic, permanently-gilled species are mud puppies of the genus Necturus, which live on bottoms of ponds and lakes; and the axolotl of Mexico.
These species never metamorphose under any conditions.
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There are other species of salamanders that reach sexual maturity with larval morphology but, unlike permanent larvae such as Necturus, may metamorphose to terrestrial forms under certain environmental conditions.
We find good examples in Ambystoma tigrinum and related species from North America.
Their typical habitat consists of small ponds that can disappear through evaporation in dry weather.
When ponds evaporate the aquatic form metamorphoses to a terrestrial form, losing its gills and developing lungs.
It then can travel across the land in search of new sources of water in which to live and reproduce.
Frogs and Toads: Order Anura (Salientia)
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The more than 3450 species of frogs and toads that comprise the order Anura are for most people the most familiar amphibians.
The Anura are an old group, known from the Jurassic period, 150 million years ago.
Frogs and toads occupy a great variety of habitats, despite their aquatic mode of reproduction and water-permeable skin, which prevent them from wandering too far from sources of water, and their ectothermy, which bars them from polar and subarctic habitats.
The name of the order, Anura, refers to an obvious characteristic, the absence of tails in adults (although all pass through a tailed larval stage during development).
Frogs and toads are specialized for jumping, as suggested by the alternative order name, Salienta, which means leaping.
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We see in the appearance and life-style of their larvae further distinctions between the Anura and Caudata.
The eggs of most frogs hatch into a tadpole (“polliwog”) stage, having a long, finned tail, both internal and external gills, no legs, specialized mouthparts for herbivous feeding (salamander larvae and some tadpoles are carnivorous), and a highly specialized internal anatomy.
They look and act altogether differently from adult frogs. The metamorphosis of a frog tadpole to an adult frog is thus a striking transformation.
The permanently gilled larval condition never occurs in frogs and toads as it does in salamanders.
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Frogs and toads are divided into 21 families. The best-known frogs families in North America are the Ranidae, which contains most of our familiar frogs, and the Hylidae, the tree frogs.
True toads, belonging to the family Bufonidae, have short legs, stout bodies, and thick skins usually with prominent warts.
However, the term “toad” is used rather loosely to refer also to more or less terrestrial members of several other families.
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The largest anuran is the West African Conraua goliath, which is more than 30 cm long from tip of nose to anus.
This giant eats animals as big as rats and ducks.
The smallest frog recorded is Phyllobates limbatus, which is only approximately 1 cm long.
This tiny frog, which can be more than covered by dime, is found in Cuba.
The largest American frog is the bullfrog, Rana catesbeiana, which reaches a head and body length of 20 cm.
CHAPTER 17
Reptiles
Enclosing the Pond
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Amphibians, with well-developed legs, redesigned sensory and respiratory systems, and modifications of the post-cranial skeleton for supporting the body in air, have made a notable conquest of land.
But, with shell-less eggs and often gill-breathing larvae, their development remains hazardously tied to water.
The lineages of reptiles, birds, and mammals developed an egg that could be laid on land.
This shelled egg, perhaps more than any other adaptation, unshackled the early reptiles from the aquatic environment by freeing the developmental process from dependence upon aquatic or very moist terrestrial environments.
In fact, the “pond dwelling” stages were not eliminated but enclosed within a series of extraembryonic membranes that provided complete support for embryonic development.
One membrane, the amnion, enclosed a fluid-filled cavity, the “pond,” within which the developing embryo floats.
Another membranous sac, the allantois, serves both as a respiratory surface and as a chamber for the storage of nitrogenous wastes.
Enclosing these membranes is a third membrane, the chorion, through which oxygen and carbon dioxide freely pass.
Finally, surrounding and protecting everything is a porous, parchmentlike or leathery shell.
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With the last ties to aquatic reproduction severed, conquest of land by the vertebrates was ensured.
The Paleozoic tetrapods that developed this reproductive pattern were ancestors of a single, monophyletic assemblage called the Amniota, named after the innermost of the three extraembryonic membranes, the amnion.
Before the end of the Paleozoic era the amniotes had diverged into multiple lineages that gave rise to all the reptilian groups, the birds, and the mammals.
Origin and Adaptive Radiation of Reptiles
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As mentioned in the prologue to this chapter, the amniotes are a monophyletic group that evolved in the late Paleozoic.
Most paleontologists agree that the amniotes arose from a group of amphibian-like tetrapods, the anthracosaurs, during the early Carboniferous period of the Paleozoic.
By the late Carboniferous (approximately 300 million years ago), the amniotes had separated into three lineages.
The first lineage, the anapsids, was characterized by a skull having no temporal opening behind the orbits, that is, the skull behind the orbits was completely roofed with dermal bone.
This group is represented today only by the turtles. Their morphology is an odd mix of ancestral and derived characters that has scarcely changed at all since the turtles first appeared in the fossil record in the Triassic some 200 million years ago.
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The second lineage, the diapsids, gave rise to all other reptilian groups and to the birds.
The diapsid skull was characterized by the presence of two temporal openings: one pair located low on the cheeks, and a second pair positioned above the lower pair and separated from them by a bony arch.
Page 326, column 2, paragraph 1:
The third lineage was the synapsids, the mammal-like reptiles.
The synapsid skull had a single pair of temporal openings located low on the cheeks and bordered by a bony arch.
The synapsids were the first group of amniotes to diversify, giving rise first to the pelycosaurs, later to the therapsids, and finally to mammals.
Characteristics and Natural History of Reptilian Orders
Anapsid Reptiles: Subclass Anapsida
Turtles: Order Testudines
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Turtles descended from one of the earliest anapsid lineages, probably a group known as the procolophonids of the late Permian, but turtles themselves do not appear in the fossil record until the Upper Triassic, some 200 million years ago.
They are enclosed in shells consisting of a dorsal carapace and a ventral plastron.
The shell is so much a part of the animal that it is fused to thoracic vertebrae and ribs.
Like a medieval coat of armor, the shell offers protection for the head and appendages, which, in most turtles, can be retracted into it.
But because the ribs are fused to the shell, the turtle cannot expand its chest to breathe.
Instead, turtles employ certain abdominal and pectoral muscles as a “diaphragm.”
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Lacking teeth, the turtle jaw is provided with tough, horny pates for gripping food.
Sound perception is poor in turtles, and most turtles are mute. Compensating for poor hearing is a good sense of smell and color vision.
Turtles are oviparous, and fertilization is internal. All turtles, even the marine forms, bury their shelled, amniotic eggs in the ground.
An odd feature of turtle reproduction is that in some turtle families, as in all crocodilians and some lizards, the nest temperature determines the sex of the hatchlings.
In turtles, low temperatures during incubation produce males and high temperatures produce females.
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The great marine turtles, buoyed by their aquatic environment, may reach 2 m in length and 725 kg in weight. One is the leatherback.
The green turtle, so named because of its greenish body fat, may exceed 360 kg, although most individuals of this economic valuable and heavily exploited species seldom live long enough to reach anything approaching this size.
Some land tortoises may weigh several hundred kilograms, such as the giant tortoises of the Galapagos Islands that so intrigued Darwin during his visit there in 1835.
Most tortoises are rather slow moving; one hour of determined trudging carries a large Galapagos tortoise approximately 300 m.
A low metabolism probably explains in part the longevity of turtles, for some are believed to live more than 150 years.
Diapsid Reptiles: Subclass Diapsida
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The diapsida reptiles, that is, reptiles having a skull with two pairs of temporal openings, are classified into three lineages.
The two with living representatives are the superorder Lepidosauria, containing the lizards, snakes, worm lizards, and Sphenodon; and the superorder Archosauria, containing the crocodilians.
Lizards, Snakes, and Worm Lizards: Order Squamata
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The squamates are the most recent and diverse products of diapsid evolution, making up approximately 95% of all known living reptiles.
Lizards appeared in the fossil record as early as the Permian, but they did not begin their radiation until the Cretaceous period of the Mesozoic when the dinosaurs were at the climax of their radiation.
Snakes appeared during the late Cretaceous period, probably from a group of lizards whose descendants include the Gila monster and monitor lizards.
Lizards: Suborder Sauria
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Lizards are an extremely diverse group, including terrestrial, burrowing, aquatic, arboreal and aerial members.
Among the more familiar groups in this varied suborder are the geckos, small, agile, mostly nocturnal forms with adhesive toe pads that enable them to walk upside down and on vertical surfaces;
the iguanas, often brightly colored New World lizards with ornamental crests, frills, and throat fans, and a group that includes the remarkable marine iguana of the Galapagos Islands;
skinks, with elongate bodies and reduced limbs; and chameleons, a group of arboreal lizards, mostly of Africa and Madagascar.
The great majority of lizards have four limbs and relatively short bodies, but in many the limbs are degenerate, and a few such as the glass lizards are completely limbless.
Page 333, column 1, paragraph 1:
Unlike turtles, snakes, and crocodilians, which have distinctive body forms and ways of life, lizards have radiated extensively into a variety of habitats and reveal an array of functional and behavioral specializations.
Most lizards have movable eyelids, where as snake’s eyes are permanently covered with a transparent cap.
Lizards have keen vision for daylight (retinas rich in both cones and rods), although one group, the nocturnal geckos, has pure rod retinas for night vision.
Most lizards have an external ear that snakes lack. However, as with other reptiles, hearing does not play an important role in the lives of most lizards.
Geckos are exceptions because the males are strongly vocal (to announce territory and discourage the approach of other males), and they must, of course, hear their own vocalizations.
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Many lizards have successfully invaded the world’s hot and arid regions, aided by characteristics that make desert life possible.
Because their skin lacks glands, water loss by this avenue is much reduced.
They produce a semisolid urine with a high content of crystalline uric acid, a feature well suited for conserving water also found in other groups that live successfully in arid habitats (birds, insects, and pulmonate snails).
Some, such as the Gila monster of the southwestern United States deserts, store fat in their tails, which they draw on during drought to provide both energy and metabolic water.
Many lizards keep their body temperature relatively constant by behavioral thermoregulation.
Worm Lizards: Suborder Amphisbaenia
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The somewhat inappropriate common name “worm lizards” describes a group of highly speicalized, burrowing forms that are neither worms nor true lizards but certainly are related to the latter.
They have elongate, cylindrical bodies of nearly uniform diameter, and most lack any trace of external limbs.
With soft skin divided into numerous rings, and eyes and ears hidden under skin, the amphisbaenians superficially resemble earthworms-a kind of structural convergence that often occurs when two very distantly related groups come to occupy similar habitats.
The amphisbaenians have an extensive distribution in South America and tropical Africa.
Snakes: Suborder Serpentes
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Snakes are entirely limbless and lack both pectoral and pelvic girdles (the latter persists as a vestige in pythons and boas).
The numerous vertebrae of snakes, shorter and wider than those of legged vertebrates, permit quick lateral undulations through grass and over rough terrain.
Page 337, column 1, paragraph 1:
In addition to the highly kinetic skull that enables snakes to swallow prey several times their own diameter, snakes differ from lizards in having no movable eyelids (snakes’ eyes are permanently covered with upper and lower transparent eyelids fused together) and no external ears.
Most snakes have relatively poor vision, the tree-living snakes of the tropical forest being a conspicuous exception.
In fact, some arboreal snakes possess excellent binocular vision, which they use to track prey through the branches where scent trails would be difficult to follow.
Snakes are totally deaf, although they are sensitive to low-frequency vibrations conducted through the ground.
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Nevertheless, most snakes employ the chemical senses rather than vision or vibration detection to hunt their prey.
In addition to the usual olfactory areas in the nose, which are not well developed, snakes have a pair of pit-like Jacobson’s organs in the roof of the mouth.
These organs are lined with an olfactory epithelium and are richly innervated.
The forked tongue, flicked through the air, picks up scent particles; the tongue is then withdrawn and sampled molecules are delivered to Jacobson’s organs.
Information is transmitted to the brain, where scents are identified.
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Snakes of the subfamily Crotalinae within the family Viperidae are called pit vipers because they possess special heat-sensitive pit organs on their heads, located between the nostrils and the eyes.
All of the best-known North American venomous snakes are pit vipers, such as the several species of rattlesnakes, water moccasins, and copperheads.
The pits are supplied with a dense packing of nerve endings from the fifth cranial nerve.
They are exceedingly sensitive to radiant energy (long-wave infrared) and can distinguish temperature differences smaller than 0.003o C from a radiating surface.
Pit vipers use the pits to track warm-blooded prey and to aim strikes, which they can make as effectively in total darkness as in daylight.
Page 338, column 1, paragraph 1:
All vipers have a pair of teeth, modified as fangs, on the maxillary bones. The fangs lie in a membranous sheath when the mouth is closed.
When a viper strikes, a special muscle and bone lever system erects the fangs as the mouth opens. The fangs are driven into a prey by the thrust, and venom is injected into the wound through a canal in the fangs.
A viper immediately releases its prey after the bite and follows it until it is paralyzed or dies. Then the snake swallows it whole.
Approximately 8000 bites but only 12 deaths from pit vipers are reported each year in the United States.
Page 338, column 2, paragraph 1:
Venomous snakes are usually divided into four groups based on the type of fangs.
The vipers (family Viperidae) have tubular fangs at the front of the mouth; this group includes the American pit vipers previously mentioned and the Old World true vipers, which lack facial heat-sensing pits. Among the latter are the common European adder and the African puff adder.
A second family of venomous snakes (family Elaspidae) has short, permanently erect fangs so that the venom must be injected by repeated bites. In this group are the cobras, mambas, coral snakes, and kraits.
The highly venomous sea snakes are usually placed in a third family (Hydrophiidae).
The very large family Colubridae, which contains most of the familiar nonvenomous snakes, does include at least two venomous (and very dangerous) snakes-the African boomslang and the African twig snake-that have been responsible for many human fatalities. Both are rear-fanged snakes that normally use their venom to quiet struggling prey.
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Most snakes are oviparous species that lay their shelled, elliptical eggs beneath rotten logs, under rocks, or in holes dug in the ground.
Most of the remainder, including all the American pit vipers except the tropical bushmaster, are ovoviviparous, giving birth to well-formed young.
Very few snakes are viviparous; in these snakes a primitive placenta forms, permitting the exchange of materials between the embryonic and maternal bloodstreams.
Snakes are able to store sperm and can lay several clutches of fertile eggs at long intervals after one mating.
The Tuatara: Order Sphenodonta
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The order Sphenodonta is represented by two living species of the genus Sphenodon.
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The tuatara is a lizardlike form 66 cm long or less that lives in burrows often shared with petrels.
They are slow-growing animals with a long life; one is recorded to have lived 77 years.
The tuatara has captured the interest of zoologists because of numerous features that are almost identical to those of Mesozoic fossils 200 million years ago.
These features include a diapsid skull with two temporal openings bounded by complete arches, and a well-developed median parietal “third eye.”
In many other respects Sphenodon resembles lizards of the early Mesozoic. Sphenodon represents one of the slowest rates of evolution known among vertebrates.
Crocodiles and Alligators: Order Crocodilia
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Crocodilians differ little in structural details from crocodilians of the early Mesozoic. Having remained mostly unchanged for nearly 200 million years, crocodilians face an uncertain future in a world dominated by humans.
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All crocodillians have an elongate, robust, well-reinforced skull and massive jaw musculature arranged to provide a wide gape and rapid, powerful closure.
Teeth are set in sockets, a type of dentition that was typical of all archosaurs as well as the earliest birds.
Another adaptation found in no other vertebrate except mammals is a complete secondary palate.
This innovation allows crocodilians to breathe when the mouth is filled with water or food (or both).
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The estuarine crocodile (Crocodylus porosus), found in southeast Asia, and the Nile crocodile (C. niloticus) grow to great size (adults weighing 1000 kg have been reported) and are swift and aggressive.
Crocodiles are known to attack animals as large as cattle, deer, and people.
Alligators are less aggressive than crocodiles and certainly far less dangerous to people.
They are unusual among reptiles in being able to make definite vocalizations. The male alligator can give loud bellows in the mating season.
In the United States, Alligator mississipiensis is the only species of alligator; Crocodylus acutus, restricted to extreme southern Florida, is the only species of crocodile.
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Alligators and crocodiles are oviparous. Usually from 20 to 50 eggs are laid in a mass of dead vegetation.
The mother hears vocalizations from the hatching young and responds by opening the nest to allow the hatchlings to escape.
As with many turtles and some lizards, the incubation temperature of the eggs determines the sex ratio of the offspring.
However, unlike turtles, low nest temperatures produce only females, while high nest temperatures produce only males.
CHAPTER 18
Birds
Birds are in the class Aves. They are endothermic vertebrates with feathers.
Endothermy is the ability to maintain a relatively stable body temperature despite fluctuations in the ambient temperature.
A less precise term is “warm blooded.”
Birds are descendants of a bipedal archosaur, perhaps an ornithischian dinosaur, if the similarity of their pelvic girdles is valid evidence.
Bipedal ornithischians could stand on their hind limbs, which freed the forelimbs for other functions including, ultimately, flight in pterosaurs and birds.
Birds have retained reptilian features such as scales (on their legs, feet, and beak) and a diapsid skull.
Feathers are exquisitely structured keratinized integumentary appendages that replace reptilian scales where feathers are present.
Feathers make flight possible in birds. Feathers also insulate against seasonal heat and high-altitude cold.
When birds produce excessive heat during flight, it is eliminated in expired air.
Feather pigments facilitate recognition by other members of the species and often provide protective coloration.
Plumage coloration can vary by age and sex, thereby signaling the reproduction state of the individual.
In addition to feathers and wings, birds have other adaptations for flight.
Body weight has been reduced in several ways to reduce the energetic cost of flight.
Long bones have become slender, and most bones, including vertebrae, lack the central marrow, which leaves cavities that contain air-filled extensions of air sacs from the lungs.
The skull has been lightened by a thinning of the compact layers of the membrane bones, but it remains durable because sutures have been eliminated in adults.
The bones of the wrist, palm, and digits have been reduced in number.
Teeth do not develop; no urinary bladder develops; the large intestine has been shortened.
There are two generally recognized subclasses of birds, Archaeornithes and Neornithes.
Subclass Archaeornithes
Two fossil birds about the size of a crow were found in Late Jurassic limestone deposits in Bavaria, Germany, in the nineteenth century.
These were given the appropriate name Archaeopteryx, the first birds.
Archaeopteryx had a long reptilian tail, teeth on both jaws, and feathers on the wings and tail that were no different from today’s.
The skull was more reptilian than avian, the nostrils were far forward, there was no beak, and the braincase had not expanded to accommodate an enlarged brain.
The sternum was small, except in the last specimen recovered.
The small sternum, which could not have accommodated strong pectoral muscles for sustained flight, suggests that these birds may have soared more than they flew.
In 1986, two crowlike fossil skeletons 75 million years older than Archaeopteryx were discovered in a mudstone quarry in Texas.
These specimens were more dinosaur-like than is Archaeopteryx, and they had smaller wings.
Whether or not they should be regarded as birds is in dispute.
Subclass Neornithes
The subclass Neornithes includes three superorders. Odontognathae, Palaeognathae, and Neognathae.
Superorder Odontognathae
Odontognaths were toothed marine birds.
The only known odontognaths are the Hesperornis and Ichthyornis species.
Hesperornis was covered with small, hairlike feathers. It had vestigial wings, so it couldn’t fly; but it had stout legs for wading, and it was a good diver. Its diet consisted of fishes that it caught with its sharp, pointed teeth.
Ichthyornis was an active flier that was able to go far offshore to feed.
Superorder Palaeognathae
Palaeognaths, known generally as ratites, have small incompetent wings, but they have powerful leg muscles that enable them to run well.
They are descendents of active fliers. Many are known as fossils only, having been depleted by human society.
Among current survivors are the rheas, ostriches, emus, and cassowaries.
The extinct moas of New Zealand were more than 3 m (8 ft) tall and they laid eggs more than 30 cm (1 ft) in diameter. Ostrich eggs weigh about 3 pounds.
Superorder Neognathae
Neognaths are, for the most part, birds that have a large carina to which relatively massive flight muscles attach. They are therefore generally known as carinates.
There are about 10,000 species and they include all living birds except the palaeognaths.
The largest living carinate is the Andean condor, with a wingspread of 3 m (10 ft) and weight of up to 14 kg (30 lbs).
The Giant Teratorn, a vulture that lived in Argentina five million years ago, had a wingspread of more than 7 m (25 ft) and an estimated weight of 23 kg (50 lbs).
Penguins have a large carina, but their forelimbs have become flippers, so they cannot fly. However, they are powerful swimmers.
CHAPTER 19
Mammals
Mammals belong to the class Mammalia. Mammals succeeded therapsid reptiles at the end of the Triassic.
They are amniotes with a synapsid skull, hair, and except monotremes, mammary glands and nipples.
Some taxonomies divide mammals into two subclasses, Prototheria, which lays eggs and has a cloaca throughout life, and Theria, which gives birth to its young.
Living prototherians are in the order Monotremata. Therians are in two infraclasses: those that have a yolk sac placenta (Metatheria) and those that have a chorioallantoic placenta (Eutheria).
Subclass Prototheria
Order Monotremata
The sole surviving monotremes are the platypus, or duckbill, Ornithorthynchus, and two genera of spiny anteaters, echidnas, all from Australia or nearby Tasmania and New Guinea.
Subclass Theria
Infraclass Metatheria
Order Marsupialia
Marsupials are primitive mammals in which the fetal yolk sac (in contact with the chorion) serves as a placenta.
The young are born in almost a larval state and are incubated and nursed after birth in a maternal abdominal pouch (marsupium) of muscle and skin until they are old enough to be independent.
In several South American genera, the pouch is incomplete or absent.
Among marsupials are kangaroos, wallabys, Tasmanian wolves, bandicoots, wombats, anteaters, and phalangers.
These and other marsupials resemble placental mammals (wolves, foxes, bears, rabbits, mice, and cats) in surprising detail.
Some phalangers resemble “flying” squirrels, and there are marsupial moles.
Infraclass Eutheria
Order Insectivora
The members of this order are primitive, generalized mammals.
Although at one time they were abundant, they are represented today by relatively few survivors, including moles, shrews, and hedgehogs.
Order Xenarthra
Xenarthrans are New World insectivorous mammals that are considerably more specialized than members of the order Insectivora.
They are armadillos, sloths, and South American anteaters.
Enlarged front claws are used for digging into ant nests or mounds and, conveniently for sloths, for hanging from the limbs of trees, which are their major habitats.
Armadillos are notable for always giving birth to identical quadruplets from a single fertilized egg.
They are also the only mammals that develop a true bony dermal armor.
Order Tubulidentata
Two species of Central and South American insectivorous aardvarks comprise the order Tubulidentata.
Their elongated snout, long sticky tongue, and strong claws on the front feet facilitate routing out and capturing insects.
Order Pholidota
Another anteater, the pangolin of Africa, is toothless and peculiarly scaly.
Order Chiroptera
Bats comprise a large mammalian order that is probably derived from a primitive insectivore.
Order Primates
Primates are primarily arboreal mammals that arose as an offshoot of Cretaceous insectivore stock.
One of many different classification schemes divides them into two suborders, Prosimii and Anthropoidea.
Suborder Prosimii
Prosimians are arboreal and mostly nocturnal primates found in the tropics of the Old World.
Lemurs receive their name from the habit of swinging silently through the forest at night. The largest lemurs are the size of a domestic cat.
Lorises, from India, Sri Lanka, and Southeast Asia, have no tail and the index finger is vestigial. In the same family are the bush babies and pottos.
Tarsiers resemble anthropoids to a greater degree than do the other prosimians.
Suborder Anthropoidea
There are two groups of anthropoids, platyrrhines and catarrhines. They are differentiated on the basis of the direction that the nostrils open.
Those of platyrrhines are separated by a broad internarial septum and open to the side.
The nostrils of catarrhines are close together and open downward.
Platyrrhines are the New World monkeys and marmosets. They include capuchins (Cebus), spider monkeys (Ateles), and howler monkeys (Alouatta).
Catarrhines are Old World monkeys, apes, and humans.
The Old World monkeys are in a separate superfamily, Cercopithecoidea.
Among Old World monkeys are baboons and macaques, or rhesus monkeys.
Apes (chimps, gorillas, orangutans) are in the pongid family, and humans are hominids (family Hominidae).
Catarrhines have no tail. A well-developed tail is present in fetal catarrhines. In humans it disappears during the third month of fetal life.
Order Lagomorpha
There are only two families of lagomorphs, the pikas, and the hares and rabbits, all of which are herbivores.
Lagomorphs differ from rodents in having two pairs of incisors on the upper jaw, a small pair lying immediately behind, not alongside of, a much larger pair.
The large front pair are rodentlike and grow throughout life. The smaller pair lack cutting edges.
Rabbits differ from hares in being born in a fur-lined nest, blind, virtually hairless, and helpless.
Hares are born without benefit of a nest, fully formed, with eyes that open within an hour. They are able to hop around before they are a day old.
Some hares of the genus Lepus acquire white fur in the winter; no rabbits do.
Pikas live above the timber line in western North America and northern Asia. They differ from rabbits and hares in having a smaller body, shorter ears, and fore and hind limbs of about equal length.
Order Rodentia
Rodents comprise the largest mammalian order and are distributed worldwide. They have a single pair of long, curved incisor teeth on each jaw that are used for gnawing.
There are four suborders, Sciuromorpha includes squirrels, chipmunks, woodchucks, gophers, beaver, and others.
Myomorpha includes micelike rodents such as rats, voles, hamsters, and lemmings.
Caviomorpha includes chinchillas.
Hystricomorpha includes porcupines.
Order Carnivora (Fissipedia)
Carnivora is a large, diverse terrestrial group some species of which have powerful jaws and sharp upper canine teeth capable of spearing and tearing flesh.
There are currently seven families of carnivores: cats (domestic cats, panthers, tigers, lynx, others), civets, hyenas, canines, bears, racoons and pandas, and mustelids (mink, otter, skunks, ferrets, badgers, others)
Not all members of the order are carnivorous, or even predominantly so.
Order Pinnipedia
These are carnivores that are morphologically and physiologically adapted for an aquatic life.
Pinnipeds are the earless (wriggling) seals, eared (fur) seals, sea lions, and walruses.
Earless seals lack the pinna of the outer ear characteristic of most mammals, but they have excellent hearing, nonetheless.
Ungulates and Subungulates
Ungulates are mammals that walk on the tips of their toes, protected by hoofs.
There are two orders: Perissodactyla and Artiodactyla.
Order Perissodactyla
There are three families of perissodactyls, horses and horselike mammals, tapirs, and rhinoceros.
They walk on the hoofed tips of one, three, or occasionally four toes and are distinguished by the fact that most of the body weight is borne on a single digit.
Perissodactyls are usually called odd-toed ungulates, but tapirs and some rhinos have four toes on the forefeet.
Order Artiodactyla
Artiodactyls are ungulates in which the weight of the body is borne on two toes.
Artiodactyls include pigs, hippopotamuses, cattle, camels, deer, antelope, and giraffes.
“Subungulate” is a term that has been applied to elephants (proboscidea), hyraxes (Hyracoidea), and manatees (Sirenia).
Order Hyracoidea
The order consists of three genera of hyraxes, with four digits on the forefeet and three on the hind feet.
Order Proboscidea
The order Proboscidea includes elephants, mastodons, and their relatives.
They have a proboscis, scanty hair, and thick, wrinkled skin.
The incisor teeth of one or both jaws are elongated to form tusks, canine teeth are absent, and the molars are large grinders, as in ungulates.
Order Sirenia
Manatees and dugongs, known also as sea cows, constitute the order Sirenia.
Order Cetacea
Today’s cetaceans (whales, dolphins, and porpoises) are permanently marine mammals.
