Mossmice

Mossmice (family muscomusidae) are descended from the Polynesian rats. They are found in the shadowforests of Antarctica. Although Polynesian rats are bad at swimming, they made their way to the Antarctic coast on ships during the end of the Holocene. These massive ships were first an attempt at settling humans in Antarctica, then at mining and oil drilling, and finally at providing safehouses from the millions that were fleeing the many wars in the Holocene. Once Antarctica was slightly habitable, the rats left the ships and failed settlements and fed on seaweed and the plants that began to colonize the shore. 

Mossmice resemble the Antechinus of modern day, with the exception of the large rodent teeth. Their reproductive cycles also line up with those of the Antechinus, the pup only ages slower. They live the same amount of time of an Antechinus as well. Many Antechinus live in Antarctica, as well as many that look just like their ancestors. Mossmice take full advantage of this fact and engage in something that is rare among mammals, brood parasitism.

Mossmice lay their offspring in the giant Antechinus dens made under the moss of the shadowforests when the pups are the same size as the out-of-pouch joeys. Mossmice are able to sneak in due to their pheromones being the exact same smell as their victims. Mossmice will plant their pups in the communal daycare and eat one of the joeys. The pups will be mistaken for the lost joey and once they hit maturity, will set off on their own before mating and continuing the process.

When they aren't eating babies, the Mossmice, as their name suggests, eat mostly moss. They nest in holes in the ground but occasionally stay in the Antechinus dens so that they can survey the area and their victims can get used to them. This is only in the darker months of the year. When the sun is out, Mossmice eat fruit and seeds.