Phenacodus primaevus (Cope 1873, Late Paleocene to Middle Eocene, 55 mya, 1.5m long) is one of the earliest and most primitive unugualtes. Likely an omnivore, all four feet had five toes. All twenty claws were modified to become hooves. The middle finger and middle toe were the longest. Note the deep narial opening. No bones are fused. 44 teeth were present.
Derived from a sister to Meniscotherium, Phenacodus gave rise to other ungulates, including Mesonyx, Hippopotamus, Tapir, Chalicotherium, Ancodus and Giraffa, but this generlized basal condylarth also gave rise to two horned taxa without modern descendants,Uintatheriumand Arsinoitherium (below).