2.1.3 Placentals

Most of the living mammals are in the subclass of placental mammals. Although there are 19 orders of placentals, most mammals belong to one of six orders, of which the largest is the rodents. One order has only one species, the aardvark. A simplified family tree of placental mammals, based on molecular evidence, is shown in Figure 14.

In this introductory course, the monotremes and marsupials are given particular focus. Although they are far less diverse than the placental mammals, their adaptations – particularly in the area of reproduction – are fascinating and informative.

Figure 13 An aardvark, Orycteropus afer

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An aardvark, Orycteropus afer.

Figure 13 An aardvark, Orycteropus afer

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Figure 14 A simplified family tree of placental mammals based on molecular evidence

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A simplified family tree of placental mammals based on molecular evidence. In each group one typical animal is illustrated. Anteaters and pangolins form a group on their own, with all the other mammals grouped in the Epitheria. There are four branches: carnivores and insectivores, primates, squirrels and ungulates. The ungulates are sub-divided into 6 groups: camels, whales, rhinos, hyrax, manatees and elephants.

Figure 14 A simplified family tree of placental mammals based on molecular evidence