Diadiaphorus is an extinct genus of litoptern mammal from the Miocene of South America. Diadiaphorus closely resembled a horse, but was only around 1.2 meters (3.9 ft) in body length, similar to a modern sheep. It had three toes, only one of which touched the ground. This toe had a large hoof; the two outer toes were rudimentary, much like those of early horses such as Merychippus. Unlike horses, however, Diadiaphorus lacked fused limb bones. Its skull was short and had a relatively large brain cavity. Judging from its low molars, Diadiaphorus ate soft vegetation, such as leaves.