Syntethoceras is a herbivore mammal (even-toed ungulate) from the late Miocene of Wyoming and Nebraska. It is the largest (~2 m. long) and the most known representative of the extinct family Proceratidae, endemic for North America. It resembles a modern antelope or goat, except for long Y-shaped single horn on the tip of its snout, which more likely has no any other purposes but modern Artiodactyla use it for.