Didelphodon

Didelphodon (meaning "opossum tooth") is a genus of stagodont marsupials from the Late Cretaceous of North America.

Description
Although perhaps little larger than a Virginia Opossum, it was one of the largest mammals of the Mesozoic. The teeth have specialized bladelike cusps and carnassial notches, indicating that the animal was a predator; the jaws are short and massive and bear enormous, bulbous premolar teeth which appear to have been used for crushing.

Paleobiology
Fossil evidence suggests Didelphodon was a small predator, perhaps filling the niche that foxes do today. The other predators of its time may have driven it underground, like a badger. Its build would certainly sustain such an existence. Heavy wear on the teeth suggests a highly specialized diet.