Wikipedia
Periptychidae
Periptychidae is a family of Paleocene placental mammals, known definitively only from North America. The family is part of a radiation of early herbivorous and omnivorous mammals classified in the extinct order Condylarthra, which may be related to some or all living ungulates (hoofed mammals). Periptychids are distinguished from other condylarths by their teeth, which have swollen premolars and unusual vertical enamel ridges. The family includes both large and small genera, with the larger forms having robust skeletons. Known skeletons of periptychids suggest generalized terrestrial habits.