In the popular imagination, marsupials are synonymous with Australia. Yet, once, in the age of Gondwanaland, Australia was linked to Antarctica (then a verdant land of forests) which was linked to South America. The marsupials have been a big part of South America’s ecosystems for a long time, but, ever since the place was overrun with placental mammals, they have kept a fairly low profile. Today’s Ferrebeekeeper post features a tremendously widespread and common marsupial from South America—yet this creature is nearly unknown beyond South America (except perhaps to mammalian zoologists and people who write alphabetical lists of beasts). The water opossum (Chironectes minimus), also known as the yapok, is the most aquatic living marsupial and the only living marsupial where both sexes have pouches.
The yapok is a formidable predator of fish, amphibians, snakes, and freshwater invertebrates like crayfish. In order to pursue these creatures underwater, it has symmetrical webbed back feet, short waterproof fur, and numerous sensory facial bristles (like a catfish! which it slightly resembles). The possums are small– 30 centimeters (11 inches) long with a 35 centimeter (14 inch) long tail. They have endearing little masks and cute stripes. Yapoks live from southern Mexico down through Central America to Southern Brazil. They are especially prevalent in Colombia and Northern Peru, but they do not live in most of the Amazon Basin.
Perhaps the most remarkable thing about yapoks is the female’s pouch. While the mother yapok is taking care of her young, she still must swim and hunt—yet marsupial babies have a lot of development to do before they can be on their own (much less swim through swift streams hunting fish). Adult female yapoks therefore have a watertight pouch which can be sealed with a muscular ring so that they can take their offspring with them in the water. For 50 days she carries her brood of 1-5 little yapoks with her everywhere…and even after then, when they detach from the nipple, they still frequent her pouch.
Of course, as I noted above, male yapoks have pouches too. Wikipedia blandly notes, “The male also has a pouch (although not as watertight as the female’s), where he places his genitalia before swimming. This is thought to prevent it from becoming tangled in aquatic vegetation and is probably helpful in streamlining the animal as well.” My mind keeps approaching this concept and then reeling back from it. So I will just leave Wikipedia’s wording as it stands and say no more.