Page 32 - Mammal (DK Eyewitness)

An early birth

Most mammals develop in their
mother’s womb (uterus). When born
they are well formed, and in many
species they are up and about within
hours of birth (p. 35). Pouched
mammals, or marsupials, don’t
follow this system. What sets
them apart from all other
mammals is the way
Australian marsupials
they reproduce. The
Eastern gray kangaroo is a typical example: its
baby grows for only five weeks in the womb.
When born it is just 1 in (2.5cm) long, naked,
blind, and unrecognizable as a kangaroo
(see opposite). It wriggles from the birth
opening (which is not the same as the birth
canal of other mammals, p. 35) to the teat
(nipple) in the mother’s pouch. As it
takes the teat in its mouth and sucks,
the teat swells and the baby is “stuck”
there as it continues to grow and
develop. The pouch, therefore, acts as
a sort of external womb where the
baby continues its development. After
a while the baby’s jaws enlarge and it
can let go of the teat. Later it grows
enough to leave the pouch for short
periods. After about 10 months the
youngster is too
big to get into
the pouch.

Adult female
red-necked wallaby

Four-month-old male
red-necked wallaby

30

(c) 2011 Dorling Kindersley. All Rights Reserved.