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2.06: The Classification of Vertebrates

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  • As we have seen above the Vertebrates are divided into 5 groups or classes namely:

    • Fish
    • Amphibia (frogs and toads)
    • Reptiles (snakes and crocodiles)
    • Birds
    • Mammals

    These classes are all based on similarities. For instance all mammals have a similar skeleton, hair on their bodies, are warm bodied and suckle their young.

    The class Mammalia (the mammals) contains 3 subclasses:

    • Duck billed platypus and the spiny anteater
    • Marsupials (animals like the kangaroo with pouches)
    • True mammals (with a placenta)

    Within the subclass containing the true mammals, there are groupings called orders that contain mammals that are more closely similar or related, than others. Examples of six mammalian orders are given below:

    • Rodents (Rodentia) (rats and mice)
    • Carnivores (Carnivora) (cats, dogs, bears and seals)
    • Even-toed grazers (Artiodactyla) (pigs, sheep, cattle, antelopes)
    • Odd-toed grazers (Perissodactyla) (horses, donkeys, zebras)
    • Marine mammals (Cetacea) (whales, sea cows)
    • Primates (monkeys, apes, humans)

    Within each order there are various families. For example within the carnivore mammals are the families:

    • Canidae (dog-like carnivores)
    • Felidae (cat-like carnivores)

    Even at this point it is possible to find groupings that are more closely related than others. These groups are called genera (singular genus). For instance within the cat family Felidae is the genus Felis containing the cats, as well as genera containing panthers, lynxes, and sabre toothed tigers!

    The final groups within the system are the species. The definition of a species is a group of animals that can mate successfully and produce fertile offspring. This means that all domestic cats belong to the species Felis domesticus, because all breeds of cat whether Siamese, Manx or ordinary House hold cat can cross breed. However, domestic cats can not mate successfully with lions, tigers or jaguars, so these are placed in separate species, e.g. Felis leo, Felis tigris and Felis onca.

    Even within the same species, there can be animals with quite wide variations in appearance that still breed successfully. We call these different breeds, races or varieties. For example there are many different breeds of dogs from Dalmatian to Chihuahua and of cats, from Siamese to Manx and domestic short-hairs, but all can cross breed. Often these breeds have been produced by selective breeding but varieties can arise in the wild when groups of animals are separated by a mountain range or sea and have developed different characteristics over long periods of time.

    To summarize, the classification system consists of:

    The Animal Kingdom which is divided into

    • Phyla which are divided into
    • Classes which are divided into
    • Orders which are divided into
    • Families which are divided into
    • Genera which are divided into
    • Species.

    Kings Play Cricket On Flat Green Surfaces” OR “Kindly Professors Cannot Often Fail Good Students” are just two of the phrases students use to remind themselves of the order of these categories - on the other hand you might like to invent your own.


    • Ruth Lawson (Otago Polytechnic; Dunedin, New Zealand)