Biology Reference
In-Depth Information
at. Far more surprising was the apparent tolerance of cats and possum for each other. Perhaps, being of
roughly equal size, neither felt threatened by the other.
Aside from being a marsupial, the central feature of possum biology is the creature's life span. For
its size, the possum is one of the shortest-lived animals in the world. Most mammals of house-cat size
see a portion of their numbers live for at least three to five years, and frequently considerably more.
House cats, for example, routinely live into their teens, and a few even manage to be around for a full
two decades. Possums, in contrast, almost never live to be more than two years old, and most fail to
make it even that far. Why is anybody's guess. Most wild animals in captivity live considerably longer
than their wild compatriots, but possums are an exception; even captive specimens rarely make it past
the age of three. Wild or captive, they apparently live life in the fast lane and simply run down after two
years or less.
Possums have enemies, of course. Perhaps the major cause of possum mortality, at least in more
heavily settled areas, is the automobile. Possums aren't swift when they cross highways, and often feed
on roadkill, thereby exposing themselves to the same agent that did in the roadkill. Possums are also
widely hunted in rural areas for their meat and fur. Still, human predation, intentional or otherwise,
seems to have little impact on the possum population. So brief is the possum's life span that much of
this mortality may only substitute for other early causes of possum demise.
Much the same can probably be said of other enemies. Owls, snakes, dogs, coyotes, and assorted
other predators take their toll. So do disease and parasites. None of this seems to matter much, though.
Possums quickly wind down and expire, even if something else doesn't get them first.
Considering the possum's exceptionally brief life, how has it managed to survive for millions of
years? Its lineage is an ancient one; its marsupial ancestors date back at least 85 million years, well into
the age of dinosaurs, and our present-day possum split off from another opossum as far back as 75,000
years ago.
The secret of the possum's survival seems to be its exceptional fecundity. A female possum bears her
first litter when she's only six to nine months old. If she lives long enough, she'll have a second litter,
but only a very few possums live long enough to have a third. A litter often consists of ten to fifteen
young—sometimes more—and averages about nine. This combination of very early reproduction and
huge litters has effectively ensured the survival of this creature and its ancestors.
As with other marsupials, possum young are born virtually in the embryonic stage. This is hardly
surprising, considering that their gestation is an astonishingly brief thirteen days! The tiny newborns
are only about the size of a raisin, and a whole litter can be fitted into a tablespoon. The most critical
moments for a newborn possum occur when the tiny, larvalike creature must make its way about two
inches to the mother's pouch. Although most succeed, some don't, and the latter simply die. Those that
reach the pouch have an excellent chance of survival as, warm and protected, they find a teat and begin
feeding. There they remain, firmly attached, for several weeks.
Possums are nocturnal, and the mother travels widely on her nightly feeding expeditions. Mean-
while, the babies go with her, riding in her pouch for about three months. This is an extremely useful
