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Phenacodontidae (superorder Protoungulata, order Condylarthra) An extinct family, comprising the best known of the condylarths, which was distributed throughout the Holarctic region from the Palaeocene to the Eocene. Early forms were small and had claws but later forms were larger and possessed more ungulate characteristics. Phenacodus, an Eocene form, was about 1.2 m long, and possessed hoofs on the ends of the phalanges of all five digits, of which the third was the longest. The dentition was complete: the canines large and the diastema small, but the molars square and bunodont. In other respects Phenacodus was relatively unspecialized. The tail was long, and the spine curved. The skull was low and long, and the brain case small.