Earth Science: Biology – Animals- Monotremes and Marsupials
Monotremes and marsupials have characteristics not seen in other mammals. Monotremes lay eggs and marsupials give birth to live young, which then climb into their mother’s pouch to nurse and mature.
The monotremes and the marsupials are among the surviving original mammals.
Monotremes
Monotremes are very unusual mammals. Two to four weeks after mating, the female lays one or two soft-shelled eggs through a cloaca, a cavity into which the intestinal and urinary canals open. The eggs are then incubated for up to ten days before they hatch.
After hatching, the babies feed on their mother’s milk—like all other mammals. The platypus has a duck-like bill protruding from a broad, flat jaw strengthened by keratin plates. Its flat, beaver-like tail and webbed front paws allow it to hunt small creatures in the water.
It lives in complex burrows in the riverbanks of Australia. Another monotreme, the echidna, lives only on land. Echidnas have strong claws to open insect nests. They use their long sticky tongues and tubular snouts to eat the insects and in case of danger they raise their spikes.
All monotremes are loners, nocturnal, or active in the dawn hours.
Marsupials
The marsupials include some 270 mammals native to Australia, Papua New Guinea, and the Americas. Marsupials on the northern continents are often similar to the eutheria (placental) mammals, but in the south they are radically different.
After birth, the tiny baby has to climb from the birth channel to the mother’s pouch using only its senses of smell and touch. Once there, it fastens onto one of the mother’s mammary glands. The baby remains inside the pouch, suckling milk until it is large enough to leave.
In the case of the red kangaroo, this suckling stage can last 235 days. The number of young born per birth varies among species up to a dozen babies, according to the degree and duration of protection they receive in the pouch.
If the stay in the pouch is short or less protected—that is, if babies are more likely to die—more off-spring will be produced to compensate for a higher rate of mortality.