Temporal range: Middle Eocene–Early Pliocene 
|Subfamilies and Genera|
†Leptotragulinae (same as Protoceratid)
|Range of Protoceratidae based on fossil record.|
Protoceratidae is an extinct family of herbivorous North American artiodactyls (even-toed ungulates) that lived during the Eocene through Pliocene at around 46.2—4.9 Ma., existing for approximately .
Protoceratidae was named by Marsh (1891). Its type is Protoceras. It was assigned to Pecora by Cook in 1934; to Ruminantia by Thurmond and Jones (1981) and Spaulding et al. (2009); to Tylopoda by Carroll and by Webb et al. in 2003. It was assigned to Artiodactyla by Marsh (1891), Hulbert and Whitmore (2006) and Prothero and Ludtke (2007). It was assigned to the infraorder Tragulina by Spaulding et al., 2009.
Physically, they resembled deer, though not directly relating to them. They ranged from 1 to 2 meters in length, from about the size of a Roe Deer to an Elk. Unlike many modern ungulates, they lacked a cannon bone in their legs. Their dentition was similar to that of modern deer and cattle, suggesting that they fed on tough grasses and similar foodstuffs, with a complex stomach similar to that of camels. It is believed that at least some forms lived in herds.
The most dramatic feature of the protoceratids, however, were the horns of the males. In addition to having horns in the more usual place, protoceratids had additional, rostral horns above their nose. These horns were either paired, as in Syndyoceras, or fused at the base, and branching into two near the tip, as in Synthetoceras. In life the horns were probably covered with skin, much like the ossicones of a giraffe. The females were either hornless, or had far smaller horns than the males, and were therefore probably used in sexual display or competition for mates. In later forms, the horns were large enough to have been used in sparring between males, much as with the antlers of some modern deer.
Genera by epoch 
- Prothero, D.R. (1998). "Protoceratidae". In Janis, C.M.; Scott, K.M.; and Jacobs, L.L. (eds.). Evolution of Tertiary mammals of North America. Cambridge: Cambridge University Press. pp. 431–438. ISBN 0-521-35519-2.
- PaleoBiology Database: Protoceratidae, basic info
- O. C. Marsh. 1891. A horned artiodactyle (Protoceras celer) from the Miocene. The American Journal of Science and Arts, series 3 41(241):81-82
- H. J. Cook. 1934. New artiodactyls from the Oligocene and Lower Miocene of Nebraska. American Midland Naturalist 15(2):148-165
- S. D. Webb, B. L. Beatty, and G. Poinar, Jr. 2003. New evidence of Miocene Protoceratidae including a new species from Chiapas, Mexico. Bulletin of the American Museum of Natural History 279:348-367
- D. R. Prothero and J. A. Ludtke. 2007. Family Protoceratidae. in D. R. Prothero and S. Foss (eds.), The Evolution of Artiodactyls 169-176
- "Relationships of Cetacea (Artiodactyla) among mammals: increased taxon sampling alters interpretations of key fossils and character evolution". PLoS ONE 4 (9): e7062. 2009. doi:10.1371/journal.pone.0007062. PMC 2740860. PMID 19774069.
- Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 272–273. ISBN 1-84028-152-9.
- Savage, RJG, & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 222–225. ISBN 0-8160-1194-X.