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

Perfect 3mm P3 with full 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.  Some paleontologists thought they might have laid eggs.  They would have resembled rodents and probably had much the same lifestyle but their teeth were different.

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