The 21 Basic Mammal Groups
Marsupials (Order Marsupialia)
Unlike the placental mammals featured elsewhere on this list — which gestate their fetuses in the womb, nourished by placentas — marsupials incubate their young in specialized pouches after an extremely short interval of internal gestation. Everyone is familiar with the kangaroos, koala bears, and wombats of Australia, but the possums of North America are also marsupials, and for millions of years the largest marsupials on Earth could be found in South America. In Australia, marsupials managed to displace placental mammals for most of the Cenozoic Era, the only exceptions being the "hopping mice" that made their way from southeast Asia, and the dogs, cats, and livestock introduced by European settlers.
The 21 Basic Mammal Group caches were placed for HNY21.