Figure 14.12: Another monotreme, the platypus, like other mammals in this order, lays eggs
and has a single opening for the urinary, genital, and digestive organs. ( 7 )
Groups of Mammals
Mammal groups, as is true for most animal groups, can be characterized a number of ways.
They can be characterized according to their anatomy, the habitats in which they live, and
their feeding habits.
Most mammals belong to the placental group. Within this group are several subgroups
including lagomorphs (i.e. hares and rabbits) and rodents (rats, mice and other small,
gnawing mammals); carnivores (cats, dogs, bears and other mammals that are primarily
meat eaters) (Figure14.15); insectivores (including moles and shrews) (Figure14.16); a
group including bats and primates; and ungulates (hoofed animals, including deer, sheep,
goats, buffalo and elephants, and also whales and manatees) (Figure14.17).
Why do you think the above groups of animals are placed together? Can you think of some
examples of tooth type that are adapted for a mammals’ diet and types of limbs that are
adapted for living in different types of habitats?
Mammals can also be grouped according to the habitat they live in and with adaptations
for living in that habitat. Terrestrial mammals with saltatory (leaping) locomotion, as in
some marsupials and in lagomorphs, is typically found in mammals living in open habitats.
Other terrestrial mammals are adapted for running, such as dogs or horses. Still others,
such as elephants, hippopotamuses and rhinoceroses, have a cumbersome (and hefty) mode
of locomotion known as “graviportal.”
Other mammals are adapted for living in trees (arboreal), such as many New World monkeys
(Figure14.18). Others are fully aquatic, such as manatees, whales, dolphins and seals, and
others are adapted for flight, as are bats, or gliding (some marsupials and rodents).