Late Jurassic (Tithonian)

Morrison Formation

Bone Cabin Quarry, Albany County, Wyoming, USA

Ultra-rare 4mm mammal jaw section with one incomplete tooth.

Mammal, Multituberculate

The mammals of the Mesozoic belong to different groups than live today.  There were no rodents, rabbits, dogs, cats, bats, deer, cattle, horses, seals, nor whales so you need an expert schooled in groups of mammals most of us have never heard of.  The mammal groups of the Jurassic are even largely different from those of the Late Cretaceous.  That was before the appearance of therian mammals (marsupials, placentals) and early in the evolution of multituberculates.