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12.3: Vertebrate Classification

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The stingray. Fish?

Of course. But what type? Of the nine classes of vertebrates, five are fish. Each of the five classes has distinguishing characteristics that allow members to be classified appropriately. Stingray are cartilaginous fish, related to sharks.

Vertebrate Classification

There are about 50,000 vertebrate species, and they are placed in nine different classes. Five of the classes are fish. The other classes are amphibians, reptiles, birds, and mammals. Table below lists some of the distinguishing traits of each class.

Class Distinguishing Traits Example
Hagfish They have a cranium but no backbone; they do not have jaws; their endoskeleton is made of cartilage; they are ectothermic.

hagfish

Lampreys They have a partial backbone; they do not have jaws; their endoskeleton is made of cartilage; they are ectothermic.

lamprey

Cartilaginous Fish They have a complete backbone; they have jaws; their endoskeleton is made of cartilage; they are ectothermic.

shark

Ray-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thin, bony fins; they are ectothermic.

perch

Lobe-Finned Fish They have a backbone and jaws; their endoskeleton is made of bones; they have thick, fleshy fins; they are ectothermic.

coelacanth

Amphibians They have a bony endoskeleton with a backbone and jaws; they have gills as larvae and lungs as adults; they have four limbs; they are ectothermic

frog

Reptiles They have a bony endoskeleton with a backbone and jaws; they breathe only with lungs; they have four limbs; their skin is covered with scales; they have amniotic eggs; they are ectothermic.

alligator

Birds They have a bony endoskeleton with a backbone but no jaws; they breathe only with lungs; they have four limbs, with the two front limbs modified as wings; their skin is covered with feathers; they have amniotic eggs; they are endothermic.

bird

Mammals They have a bony endoskeleton with a backbone and jaws; they breathe only with lungs; they have four limbs; their skin is covered with hair or fur; they have amniotic eggs; they have mammary (milk-producing) glands; they are endothermic.

bear

Summary

  • The 50,000 species of living vertebrates are placed in nine classes: hagfish, lampreys, cartilaginous fish, ray-finned fish, lobe-finned fish, amphibians, reptiles, birds, and mammals.

Practice

Use this resource to answer the questions that follow.

  1. What were the first jawed vertebrates? How are these two groups distinguished?
  2. Describe possible predecessors to land animals.
  3. What are tetrapods?
  4. What were the first tetrapods? Where must these animals live?
  5. What adaptations allowed animals to become less dependent on water?
  6. What animals are amniotes?
  7. What characteristics define mammals?

Review

1. Which was the first vertebrate class to evolve?

2. What are the five fish vertebrate classes?

3. What are the defining characteristics of mammals?

Vocabulary

amphibian

amphibian

Ectothermic, tetrapod vertebrate that divides its time between freshwater and terrestrial habitats.
bird

bird

Bipedal, endothermic, tetrapod vertebrate that lays amniotic eggs and has wings and feathers.
cartilaginous fish

cartilaginous fish

Ectothermic fish with an endoskeleton made of cartilage; have a complete backbone and jaw.
lamprey

lamprey

Ectothermic fish with a partial backbone; do not have jaws; endoskeleton is made of cartilage.
lobe-finned fish

lobe-finned fish

Ectothermic fish with a backbone and jaw; endoskeleton is made of bones; have thick, fleshy fins; one of two types of bony fish.
mammal

mammal

Endothermic, tetrapod vertebrate that lays amniotic eggs and has mammary glands (in females) and hair or fur.
ray-finned fish

ray-finned fish

Ectothermic fish with a backbone and jaws; endoskeleton is made of bones; have thin, bony fins; one of two types of bony fish.
reptile

reptile

Ectothermic, tetrapod vertebrate that lays amniotic eggs; includes crocodiles, lizards, snakes, and turtles.

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Date Created:

Feb 24, 2012

Last Modified:

Nov 11, 2014
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