Late Cretaceous (Maastrichtian)

Hell Creek Formation

Powder River County, MT, USA

Very fine 18mm jaw section with p4 and erupting incisor.

Great example of this early mammal

Mammal, Multituberculate

Some people refer to this animal and its relatives as “rodents” but true rodents didn’t appear until the Late Paleocene.  Mesodma was a genus of the Order Multituberculata, a branch of mammals entirely separate from any that live today.  They would have resembled rodents and probably had much the same lifestyle but they had different teeth as seen in the lower fourth premolar which was an enlarged shearing tooth perhaps for cutting into large seeds or slicing up fruit or even small prey.