The water opossum (Chironectes minimus), also locally known as the yapok (/ˈjæpɒk/), is a marsupial of the family Didelphidae.

The forefeet can be used to feel for and grab prey as the animal swims, propelled by its tail and webbed back feet.

[citation needed] Being a marsupial and at the same time an aquatic animal, the water opossum has evolved a way to protect its young while swimming.

A strong ring of muscle makes the pouch (which opens to the rear) watertight, so the young remain dry, even when the mother is totally immersed in water.

[citation needed] Water opossums mate in December and a litter of 1–5 young is born 12 to 14 days later in the nest.

The mandibular fossils, MACN 2464 and 3515 were known to be from the water opossum because their teeth were nearly indistinguishable from living populations of the organism in present day.