Mesodma sp.
Multituberculate
Late Cretaceous
Hell Creek Formation
Powder River County, Montana, USA

Excellent 3mm P4 with roots.

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 once 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.