Ancestor of all cows and deer discovered

Two small mammals illustration in a forest
Reconstruction of Militocodon lydae. Credit: Denver Museum of Nature & Science.

An unassuming little mammal which lived 65 million years ago, just after the extinction of the dinosaurs, has been identified as the ancestor of all modern hoofed animals.

Its descendants include cows, deer and pigs.

Militocodon lydae was discovered in the US state of Colorado. At between 270 and 450 grams, the animal would have been about the size of a modern brown rat. It is known from a partial skull and jaw remains, and is described in a paper published in the Journal of Mammalian Evolution.

The creature’s fossils are from a layer only 610,000 years after the extinction event which saw the end of the “Age of the Dinosaurs.”

Militocodon was alive during the early Palaeocene (66–56 million years ago), an era which also saw the emergence of the first primate, Purgatorius.

The dental remains of Militocodon suggest an evolutionary development away from grinding motions toward shearing and crushing in chewing. It is part of a family of ancient mammals called periptychids which are believed because of their teeth to be the ancient predecessors of all ungulates – hoofed mammals.

The authors note that M. lydae’s discovery is yet another indication of the ascendancy of mammals after the demise of the non-avian dinosaurs.

Coming out of the shadows, mammals were experimenting with new forms. Between 56 and 50 million years ago, mammals began conquering the skies and the seas with the emergence of the ancestors of whales and bats.

“Rocks from this interval of time have a notoriously poor fossil record and the discovery and description of a fossil mammal skull is an important step forward in documenting the earliest diversification of mammals after Earth’s last mass extinction,” says senior author Tyler Lyson, a curator at the Denver Museum of Nature & Science.

Understanding how life rebounded after the mass extinction event 66 million years ago is made difficult by the lack of fossil evidence.

New remarkably well-preserved fossils from Colorado dating to the Palaeocene may help piece this period together.

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