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12.34: Mammal Classification

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    6737
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    How would you classify this mammal?

    Obviously it is a camel, but is there more to it than that? There are 17 orders of placental mammals. But then these mammals need to be further classified into families, genera, and finally species.

    Classification of Placental Mammals

    Traditional classifications of mammals are based on similarities in structure and function. Increasingly, mammals are being classified on the basis of molecular similarities. DNAanalyses has recently shown that the traditional orders include mammals that may not be closely related.

    Traditional Classification

    The most widely accepted traditional classification of mammals divides living placental mammals into 17 orders. These orders are shown in Table below. This classification of mammals was widely accepted for more than 50 years. Placental mammals are still commonly placed in these orders. However, this classification is not very useful for studies of mammalian evolution. That’s because it groups together some mammals that do not seem to be closely related by descent from a recent common ancestor.

    Order Example Sample Trait
    Insectivora

    mole

    f-d:69503d2e01ef10a81dbba3d7088a16ac42f3e654c6641966240d0986 IMAGE_TINY IMAGE_TINY.1

    small sharp teeth
    Edentata

    anteater

    f-d:5c211c5d61d86ee53468051a5b9b8ce3ea641a23c0b29698e0787f50 IMAGE_TINY IMAGE_TINY.1

    few or no teeth
    Pholidota

    pangolin

    f-d:51bfa3cf252dafe10de12817d12fc8f5eb18680926745a681c9392e2 IMAGE_TINY IMAGE_TINY.1

    large plate-like scales
    Chiroptera

    bat

    f-d:985d3e919eb42f8b16cb302517fee810eadea4f8a8f173adf3e73594 IMAGE_TINY IMAGE_TINY.1

    digits support membranous wings
    Carnivora

    coyote

    f-d:21313aa8a8329b3978eebfdc0916b7254f30d04b9ab6ca542fbb921d IMAGE_TINY IMAGE_TINY.1

    long pointed canine teeth
    Rodentia

    mouse

    f-d:63c9f5e1a8f3aff077e51b6add69ef3f06609e2ae790b8b5507e46c3 IMAGE_TINY IMAGE_TINY.1

    incisor teeth grow continuously
    Lagomorpha

    rabbit

    f-d:247c7a2332fe8b3013da3f2f7af23bd2ba308cc63ded0319b87fb972 IMAGE_TINY IMAGE_TINY.1

    chisel-like incisor teeth
    Perissodactyla

    horse

    f-d:4c5de92bdbe9dcfd13b623995b0c8003fca24b44d43bb45c20e76849 IMAGE_TINY IMAGE_TINY.1

    odd-toed hooves
    Artiodactyla

    deer

    f-d:7f1efd12f6b166b44c86c658eebc49ec01a2a8bc18c7b87a7287ad7e IMAGE_TINY IMAGE_TINY.1

    even-toed hooves
    Cetacea

    whale

    f-d:3dc47d40189ff027a216465aa65046b732aeb8525212a06b7ff87cf9 IMAGE_TINY IMAGE_TINY.1

    paddle-like forelimbs
    Primates

    monkey

    f-d:9bf8b67c9a8267ca6131e49542dc11a6ab4126c7eb97c3e9d2222b32 IMAGE_TINY IMAGE_TINY.1

    five digits on hands and feet
    Proboscidea

    elephant

    f-d:ed3b170e7f2199cfd4d070f9d140488dad89d2e5cbb0d470d896cfa2 IMAGE_TINY IMAGE_TINY.1

    tusks
    Hyracoidea

    hyrax

    f-d:ad253ef81878f054330d496966323d857b95b84720174701b5beabcc IMAGE_TINY IMAGE_TINY.1

    rubbery pads on feet
    Dermoptera

    colugo

    f-d:b544f13944fdb6a3d24711e7adcf2a66084bf6c4494e8b706d278b40 IMAGE_TINY IMAGE_TINY.1

    membrane of skin between legs for gliding
    Pinnipedia

    seal

    f-d:2053ab18cee260f481bb98af992329bdba160c2519a79c673e682c3a IMAGE_TINY IMAGE_TINY.1

    feet with fins
    Sirenia

    manatee

    f-d:8a415b14d1daae4c97be6240d20b3cfd638ee5319db5167a5eac14a3 IMAGE_TINY IMAGE_TINY.1

    paddle-like tail
    Tubulidentata

    aardvark

    f-d:4296b35513bf6697fd0c93958554de22c9ecee03df2a2232e21d7206 IMAGE_TINY IMAGE_TINY.1

    teeth without enamel

    Phylogenetic Classification

    The mammalian supertree classifies placental mammals phylogenetically. It uses the analysis of DNA sequences to group together mammals that are evolutionarily closely related, sharing a recent common ancestor. These groups are not necessarily the same as the traditional groups based on structure and function.

    The supertree classification places placental mammals in four superorders. The four superorders and some of the mammals in them are:

    • Afrotheria—aardvarks, elephants, manatees.
    • Xenarthra—anteaters, sloths, armadillos.
    • Laurasiatheria—bats, whales, hoofed mammals, carnivores.
    • Supraprimates—primates, rabbits, rodents.

    All four superorders appear to have become distinct from one another between 85 and 105 million years ago. The exact relationships among the superorders are still not clear. Revisions in this classification of mammals may occur as new data become available.

    Summary

    • Mammals used to be classified on the basis of similarities in structure and function into 17 different orders.
    • Recently, DNA analyses have shown that the traditional orders include mammals that are not closely related.
    • Phylogenetic classification, based on DNA data, groups placental mammals in four superorders. The superorders appear to have become distinct from each other 85–105 million years ago.

    Review

    1. Compare traditional and phylogenetic classifications of placental mammals. Explain which type of classification is more useful for understanding how mammals evolved.
    2. Assume that a new species of placental mammal has been discovered. Scientists have examined it closely and studied its DNA. It has wings similar to a bat that it uses for gliding. Its DNA is most similar to the DNA of rodents such as mice. How would you classify the new mammal? Explain your answer.

    12.34: Mammal Classification is shared under a CK-12 license and was authored, remixed, and/or curated by CK-12 Foundation via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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