Rugosodon

Rugosodon is an extinct genus of multituberculate (rodent-like) mammals from eastern China that lived 160 million years ago during the Jurassic period. The discovery of its type species Rugosodon eurasiaticus was reported in the 16 August 2013 issue of Science. The species is the oldest so far described in the multituberculate family, the most successful and long-lasting lineage of all mammals.

Rugosodon is represented by a nearly complete fossilized skeleton, including a skull, that bears a strong resemblance to a small rat or a chipmunk. The mammal is estimated to have weighed between 65-80 g, about that of an average chipmunk. The generic name Rugosodon (Latin for "wrinkly tooth") refers to the rugosity, or wrinkliness, of the distinctively shaped teeth. Its teeth indicate that the animal was an omnivore, well-adapted to gnawing both plants and animals, including fruits and seeds, worms, insects and small vertebrates. Its ankle joints were highly mobile at rotation, a characteristic of mammals living in trees. This means that the ankle is remarkably flexible, allowing the foot to hyper-extend downward — like a ballerina standing on pointed toes — and to rotate through a wide range of motion. This feature, along with highly mobile digits, defines the multituberculates and is not seen in other mammalian lineages of the era. Rugosodon also had a highly flexible spine, which would have allowed it to twist both left to right and front to back.