Review sheet Ch. 34 Vertebrates
1) Phylum Chordata is characterized by: 1) Notochord: a long flexible rod between the digestive tract
and the nerve cord. It functions as a support structure and in most chordates degenerates when embryo
develops into adult. 2) Dorsal hollow nerve cord (in other phyla nerve cords are solid and ventral); in
vertebrates nerve cord develops into spinal cord and brain. 3) Pharynx and pharyngeal slits: region
of digestive tract near mouth. Slits allow swallowed water to pass out of digestive tract without
passing through entire tract. The pharynx develops into different structures in different groups of
chordates.
4) Muscular, post-anal tail: found in all chordate embryos, modified for different
functions in different chordates.
2) Tunicates or sea squirts: larva have all the chordate characteristics and swim until the settle in the
substratum. They develop into adults that lack a notochord, nerve cord, and tail. They are usually
sessile and feed by straining particles from water that flows through their pharynx.
3) Lancelets: Are the most basic chordates in that they retain all four of the basic chordate traits
throughout their lifecycle. Most species burrow in sand with only their head exposed, and feed on
particles collected from the water. Not sessile because they frequently swim to other locations in the
sand.
4) Paedogenesis a kind of evolutionary change where sexual maturity is attained at a more immature
stage of development. It is believed that cephalochordates evolved from ancestors similar to the
urochordates that evolved in such a way that their development climaxed during their larval stage of
development.
5) The following chordates are craniates. This means that they have a head (brain, sensory organs and a
skull of some kind).
6) Hagfish: These are agnathan (no jaws). Notochord persists in a adult form. Member of the
phylogenetic group Vertebrata, but does not have an actual vertebral column. Mostly bottom feeding
scavengers.
7) The following groups of chordates are vertebrates. This means they have connective tissue dorsal to
the nerve cord that develops into the vertebral column.
8) Lampreys: Agnathan (no lower jaw). Notochord persists in adult form. Have a pipe of cartilage with
projections that partially cover nerve cord (primitive vertebral column). Many species latch onto other
fish, cut them with their rasping tongue and drink their blood.
9) Class Chondrichthyes (sharks and rays): Cartilaginous skeleton (derived form bony ancestor).
Anterior pharyngeal gill arches are modified into lower jaw, allowing biting and grasping of prey.
Have two sets of paired fins. The anterior pair is the pectoral fins and the posterior pair is the pelvic
fins. Pairs of pectoral (e.g. human arms) and pelvic (e.g. human legs) appendages are present in all of
the following classes as well.
10) Three forms of reproduction are found in Class Chondrichthyes (as well as other vertebrate groups):
oviparous reproduction
Laying an egg that hatched outside the mother’s body
ovoviviparous reproduction
Forming an egg that hatches within the mother’s body
viviparous reproduction
When young develop within a uterus within the mother
11) Class Osteichthyes (bony fish) These are fish with bony skeletons, gills covered by an operculum, and
swim bladders. There are three main groups of extant bony fish: 1) Ray-finned fish: Most of the fish
we think about are ray-finned fish (e.g. goldfish, salmon, tuna, minnows, trout, catfish, clown fish,
etc.). Unlike sharks, they have bony skeletons and their fins are supported by long, flexible struts
(“rays”). 2) Lobe-finned fish: include coelacanths: Have fleshy, muscular fins supported by the bony
skeleton, unlike ray-finned fish. Coelacanths are very rare in present times and were thought to be
extinct until 1938. Closer to tetrapods (legged vertebrates) than the ray-finned fishes. Another group
of lobefinned fish are Lungfish: Have lungs and can breath air. Air-breathing has also evolved on
separate occasions in different groups of fish (e.g. eels). A third extant lineage within the lobe-finned
fish clade are the tetrapods.
12) Tetrapods are vertebrates with sturdy legs supported by the skeleton. This includes vertebrates that
have lost legs secondarily (e.g. snakes, whales, etc.). The first tetrapods were almost certainly fish that
lived in shallow waters where legs are more practical than fins. Legs can be used for walking on
sediment in shallow pools, or for crawling through vegetation in shallow water. Likewise air-breathing
probably evolved in fish as an adaptation to stagnant waters with little dissolved oxygen. Legs and
lungs were not initially adaptations to a terrestrial lifestyle.
13) Members of Class Amphibia were the first vertebrates to spend significant periods of time on land.
They have a dual stage development: 1) tabpole larva; 2) adult. Their eggs lack shells and must be laid
and incubated in water to survive. Adults can breathe using lungs or through their moist skin, which
also allows them to exchange gases in water. Some species lack lungs entirely and only breathe
through skin. The three extant groups of amphibians are Anurans (frogs), salamanders, and Apoda
(legless amphibians).
14) Phylogenetically , there are three clades of amniotes: the anapsid clade, of which only turtles
survive; the diapsid clade (a diverse group that includes birds); and the synapsid clade, of which the
only extant member is Class Mammalia. Amniotes have eggs with a waterproof shell. Thus, amniotes
do not depend on bodies of water for successful reproduction. Viviparous amniotes, including most
mammals, have a uterus which takes the place of the waterproof egg.
15) Reptiles consist of four clades from the anapsid and diapsid clades. They are characterized by
keratinized skin scales. These scales limit skin permeability so reptiles cannot breathe through their
skin like amphibians do. However, this also protects them from drying out. Reptiles have internal
fertilization. Usually oviparous, but some have ovoviviparous or viviparous.
16) The one extant branch of the anapsids are turtles.
17) The four extant branches of the diapsid clade are 1) tuataras; 2) Squamata (lizards and snakes); 3)
crocodilians; 4) birds
18) The only extant branch of the synapsids are mammals.
19) Birds are a highly derived clade of diapsids, with many traits that distinguish them from the four reptile
diapsid clades. They are the closest living relatives of the crocodilians, and are the only survivors of
the dinosaur clade. Birds appeared around 150 million years ago. Like reptiles, they have scales on
their legs and amniotic eggs.
20) The most obvious feature of birds is flight, and they are highly modified structurally for flight,
although some birds have a derived flightless condition (e.g. ratites).
a) honeycombed, “hollow” bones for lightness
b) a beak, which is lighter than a toothed jaw
c) a gizzard for grinding food (reduces need for a heavy jaw)
d) high metabolic rate/endothermy, which allows for the high levels of activity necessary for flight
e) acute vision to maneuver and avoid crashes; olfaction (sense of smell) usually poor
f) forelimbs modified as wings
g) feathers (insulation and flight)
h) sternum modified as a keel for attachment of massive flight muscles
21) Class Mammalia originated about 220 million years ago. They were not prominent until 65 million
years ago when the Cretaceous extinctions wiped out he dinosaurs and other large vertebrate species.
22) Mammals have mammary glands, glands on the ventral surface that secrete milk to nourish young.
Appear to be modified sweat glands.
23) Mammals have hair.
24) Mammals have large brains, high intelligence and complex behaviors.
25) Mammals have specialized teeth (e.g. canines, incisors, teeth for shearing, teeth for grinding, etc.). In
contrast reptile teeth vary little in shape and function.
26) One major grouping of mammals are the monotremes (egg-laying mammals). They lay amniotic
eggs, have a cloaca (a single urogenital opening, where urine, feces, and sex cells are all emitted).
They secrete milk from the bellies like sweat (no nipples) and offspring lick it off their fur. The are
only four extant species: the platypus and three species of echidna (spiny anteater). They all are native
to Australia.
27) Marsupials, the second major group of mammals, produce offspring that are very immature (legless,
etc.). After birth, their offspring crawl to the mother’s pouch and suckle at a mammary until they
develop to infancy before leaving. With the exception of opossums, marsupials are all native to
Australia. From the perspective of evolutionary biology, marsupials are interesting because there are
many cases of convergent evolution between marsupials in Australia and placental mammals in the
rest of the world. E.g. kangaroo is very similar in body shape and niche to the Patagonian cavi; there
are marsupial mice in Australia that are not of the Eutherian order Rodentia, but function very much
like rodents in the ecosystems of Australia.
28) Eutherians (placental mammals) have a longer gestation period than marsupials and are born more
mature. All of the native mammal species in the world outside of Australia are eutherians (exception:
opossums are native to South America). The following are major orders of eutherian mammals.
29) Order Chiroptera (bats): two major groups: 1) Megachiroptera (fruit bats): relatively large, lack
sonar, excellent night vision; generally eat fruit; 2) Microchiroptera (little brown bat, vampire bat,
etc.): generally small (smaller than most rodents); use sonar; mostly eat insects
30) Order Perrisodactyla (odd-toed hoofed mammals): include horses (one toe) and rhinos (three toes).
31) Order Artiodactyla (even-toed hoofed mammals): include deer, cattle, pigs, giraffes, gazelles, etc.
32) Order Carnivora (cats, dogs, ferrets, otters, seals, walruses, bears, raccoons, pandas, mongooses,
hyenas, etc.): have pronounced canines and teeth for shearing flesh; not necessarily carnivorous (e.g.
pandas eat bamboo)
33) Order Primates (prosimians, old and new world monkeys, apes (including humans)): large brains,
hands for climbing
34) Order Lagomorpha (rabbits, hares, and pikas) skulls similar to rodents, but twice as many incisors
and honeycombed skulls
35) Order Rodentia (mice, rats, pocupines, squirrels, prairie dogs, woodchucks, capybarsa, beavers, etc.)
have chisel-like incisors that grow continuously. Large toothless gap between incisors and molars.
Amniotes
Anapsids
turtles
crocodilians
Diapsid
archosaurs
birds
Synapsid
lepidosaurs
tuataras
mammals
Squamata (lizards and snakes)