Late Cretaceous (Maastrichtian)

Hell Creek Formation

Harding County, South Dakota, USA

8mm wide premolar of the largest known Cretaceous mammal

Mammal, Marsupial.

Didelphodon is a genus of marsupial from the Late Cretaceous of North America.  In fact it lived during the last 4-5 million years of the period, the same time as Tyrannosaurus and Triceratops.  It was about the size of a large opossum but might have looked more like a long-legged otter, and in fact, it may have occupied the same niche as that semi-aquatic carnivore.

The Late Cretaceous was a time when marsupials were common in North America, but most including Didelphodon, died out during the K/T extinction.