Trispondylus Cope, 1884 Phenacodus (Greek: "deception" (phenax), "tooth' (odus)[2]) is an extinct genus of mammals from the late Paleocene through middle Eocene, about 55 million years ago.

[3] The typical Phenacodus primaevus was a relatively small ungulate about 1.5 m (4 ft 11 in) long and weighed up to 56 kg (123 lb), of slight build, with straight limbs each terminating in five complete toes, and walking in the digitigrade fashion of the modern horse.

[4][5] The middle toe was the largest, and the weight of the body was mainly supported on this and the two adjoining digits, which appear to have been encased in hooves, foreshadowing the tridactyl type common in perissodactyls and certain extinct groups of ungulates.

The skull was small, with proportionately minute brain; and the arched back, strong lumbar vertebrae, long and powerful tail, and comparatively feeble fore-quarters all proclaim kinship with the primitive carnivores Creodonta.

In the early Paleocene of North America, the place of the above species was taken by Tetraclaenodon puercensis, an animal only half the size of P. primaevus, with the terminal joints of the limbs intermediate between hoofs and claws, and the first and fifth toes taking their full share in the support of the weight of the body.