Interesting Facts About Marsupials

When people think of marsupials, they often think of koala bears and kangaroos. However, there are many different species of marsupial on the planet and many more once existed. They are very interesting creatures in that they are mammals, but their reproduction process is quite different from other mammals. They are also interesting in that they present us with clear examples of convergent evolution when they are compared to other mammals. Here are a few more interesting things that you might not have known about marsupials.

The main difference between marsupial mammals and ‘placental’ mammals is the length of gestation in females and also the birthing of offspring. Marsupials give birth to live young. However, their young is very small and helpless given the fact that marsupial gestation periods can be as short as a matter of days. The young climb out of their mother’s womb in this state and then cling to their mother’s teats, suckling for nourishment until they are big enough to let go and survive.

Marsupials are sometimes called “pouch mammals.” This is a bit of a misnomer. While most female marsupials do have a pouch which covers their teats and their developing young, not all do. Some marsupials have only folds of skin for their young to develop near. Others have no pouch at all. For those unfortunate marsupials whose mothers have little or no pouch, it is difficult. They must hang onto their mother’s teats for dear life, literally.

Speaking of misnomers, the term ‘placental mammal’ is a little misleading. It isn’t that marsupials don’t develop a placenta.  It is that theirs is very different from that of other mammals. The marsupial placenta is incapable of sustaining young for very long, whereas a ‘placental mammal’ can gestate for a longer amount of time, giving their young more time to develop.

Marsupials and placental mammals give us great examples of convergent evolution. Convergent evolution happens when two species that don’t have a recent common ancestor develop the same traits and fill the same ecological niche. For example, canids are placental mammals and they evolved in much the same way as the now extinct Thylacine did. Many canids are very similar in form and function as the Thylacine was. This is because the ecological niche needed to be filled and the climates, available resources, etc., were very similar.

Long ago, during the Mesozoic, there were more marsupials in the United States than there were placental mammals. Today, there is only one marsupial that naturally occurs in the United States and that is the opossum. Some other continents that were once home to many species of marsupial now have very few. However, they flourish in Australia where there are more than 200 species of marsupial. Many of them are indigenous to the continent.

Sources

Marsupial Mammals, retrieved 3/7/10, ucmp.berkely.edu/mammal/marsupial/marsupial.html

Marsupial: A southern survival story, retrieved 3/7/10, paleocene-mammals.de/marsupials.htm