Vertebrate Classification, BIO 3220

Superclass: AGNATHA (jawless vertebrates)

No paired fins, cartilaginous skeleton, no scales, but bony dermal plates in Ostracoderms, cranium but no vertebrae



[lampreys, Ammocoetes larvae, hagfishes/ slime eels]

Lampreys are parasitic, and spawn in fresh water to Ammocoetes larvae. Hagfish are bottom scavengers.


 Superclass: GNATHOSTOMATA (jawed vertebrates)

 *Class: ACANTHODII (armored Paleozoic jawed fishes)

Probably the oldest jawed fish. Spiny projections, dermal armor, paired fins, operculum, ranged from a few inches up to 2 meters


 *Class: PLACODERMI (placoderms; armored jawed fishes)

Plate-like armor, abundant in Devonian Period, cartilaginous skeleton, up to 10 meters long!

 Class: CHONDRICHTHYES (cartilaginous fish)

Arose in Devonian period, placoid scales, great sense of smell, lateral line system, ventrally positioned mouth.

 subclass: Elasmobranchii

[sharks, rays]

subclass: Holocephali

[chimeras or rat fish]


BONY FISH; OSTEICHTHYES – over 20,000 species

 Class: Actinopterygii (ray-finned fish)

Operculum, bony skeleton, terminal mouth, swim bladder in most

subclass: Chondrostei [sturgeonspaddlefish]

subclass: Neopterygii

order: Holostei [garsbowfin] {order: Lepisosteiformes and Amiiformes per Kent.}

Gars have ganoid scales, Amia (bowfin) has modern scales

division: Teleostei [teleost fish]

95% of all bony fish are in this division. They possess light modern cycloid or ctenoid scales.

 Class: Sarcopterygii (fleshy-finned fish)

superorder: Dipnoi [lungfish]

superorder: Crossopterygii

[lobe-finned fish]

Ancestor of amphibian, common in Devonian Period, extinct except Latimeria discovered off of South African Coast in 1938.


Class: AMPHIBIA (amphibians)

“Both Life”, Fewest numbers of species of all classes. Changes present for adaptation to terrestrial life. Land has many habitats, more oxygen than water, but is less dense for supporting body than water. The temperature fluctuates more on land.

 *subclass: Labyrinthodontia


Oldest tetrapod, from about 350 mya. Minute dermal scales, ray-fin tail, skull similar to Crossopterygian, sensory structures for aquatic environment. Gave rise to Reptiles.

 subclass: Lissamphibia

“Smooth amphibians”. Origin may be monophyletic from the Labyrinthodont, or diphyletic with Anurans arising from Labyrinthodonts and Urodeles and Apodans separately from Crossopterygians. Features include moist glandular skin, no scales, keratinized skin, double circuit circulatory pattern.

*order: Proanura


order: Anura [frogs, toads]


order: Urodela [tailed amphibians, salamanders, Necturus]


order: Apoda [caecilians]

Burrow in swampy areas, many are blind


Class: REPTILIA (reptiles)

“Creeps”, originates in mid-Carboniferous Period with the Cotylosaurs and are dominant through the end of the Cretaceous Period. Originated from Labyrinthodonts. Reptiles are amniotes, have eggs with shells, keratinized skin with scales, imperfect 4-chambered heart, stronger skeleton & muscles than previous groups. Classified according to temporal arches.

 subclass: Anapsida [*stem reptiles – Cotylosaurs, turtles]


 subclass: Lepidosauria

Lepidosauria is the most successful group of reptiles [lizards, snakes, amphisbaenians, Sphenodon]


 subclass Archosauria [crocodiles, *dinosaurs, *flying reptiles, *thecodonts]


*subclass Euryapsida – Sauropterygia, Ichthyosauria [plesiosaurs, fishlike reptiles]


 *subclass: Synapsida [mammal-like reptiles – therapsids]

Single temporal fossa, size of a large dog, Permian-Jurrassic Periods, ancestor of mammals.



Class: AVES (birds)

Originated from bipedal dinosaurs, Archaeopteryx in Jurassic Period, have feathers, modern birds have no teeth, are endothermic, four-chambered heart, have great social organization and complex behaviors.


 *subclass: Archaeornithes [ancestral birds – Archaeopteryx]


 subclass: Neornithes [familiar birds]

 Class: MAMMALIA (mammals)

Originated from Therapsids, have hair, mammary glands, 4-chambered heart, non-nucleated RBCs, endothermic, diaphragm for breathing, extensive cerebral cortex, and dentary bone is sole lower jaw bone.

 subclass: Prototheria [egg-laying mammals (oviparous); monotremes are the only living order, platypus, echidnas= spiny anteater]


 subclass: Theria

infraclass: Metatheria [yolk sac serves as placenta; pouched mammals; opossum, wallaby, kangaroo]


 infraclass: Eutheria [true placental mammals; viviparous]


*denotes extinct taxa