Ctenacodon
Mammal
Late Jurassic (Tithonian)
Morrison Formation
Bone Cabin Quarry, Albany County, Wyoming, USA

Ultra-rare 3mm multituberculate mammal incisor (I2).

Ctenacodon is a genus of the Order Multituberculata, a branch of mammals unrelated to any that live today.  They would have resembled rodents and probably had much the same lifestyle but they had a distinctive dentition as exemplified by the lower fourth premolar which had become an enlarged shearing tooth perhaps for cutting into large seeds or slicing up fruit or even small prey.

Ctenacodon lived over 80 million years before the multituberculates (Mesodma, Meniscoessus) of the Hell Creek Formation.