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12.4: Vertebrate Classification

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    6707
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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 amphibiansreptilesbirds, and mammals.Table below lists some of the distinguishing traits of each class. Classes are listed in order of evolution.

    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, amphibiansreptilesbirds, and mammals. 

    Review

    1. Which was the first and last vertebrate classes to evolve?
    2. What are the five fish vertebrate classes?
    3. What are the defining characteristics of mammals?
    4. What was the first class of vertebrates to live on land?
    5. Sharks belong to what vertebrate class?