Late Cretaceous (Maastrichtian)
Hell Creek Formation
Powder River County, Montana, USA

Fine 2mm M1 with roots

Mammal, Multituberculate.

Mesodma is a genus of the Order Multituberculata, a branch of Jurassic-Eocene mammals entirely separate from any mammal groups that live today.  They would have resembled rodents and probably had much the same lifestyle but they had a different dentition as seen especially in the shape of the lower third premolar.

Mesodma was one of the multituberculates that survived into the Early Paleocene after the K/T mass extinction.