The hoof (pl.: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering.[1] Artiodactyls are even-toed ungulates, species whose feet have an even number of digits; the ruminants with two digits are the most numerous, e.g. giraffe, deer, bison, cattle, goat, pigs, and sheep.[2] The feet of perissodactyl mammals have an odd number of toes, e.g. the horse, the rhinoceros, and the tapir.[3] Although hooves are limb structures primarily found in placental mammals, hadrosaurs such as Edmontosaurus possessed hoofed forelimbs. The marsupial Chaeropus also had hooves.[4]
- ^ "the definition of hoof". Dictionary.com. Retrieved 2016-11-30.
- ^ Keller, Anna; Clauss, Marcus; Muggli, Evelyne; Nuss, Karl (2009-07-15). "Even-toed but uneven in length: the digits of artiodactyls" (PDF). Zoology. 112 (4): 270–278. doi:10.1016/j.zool.2008.11.001. PMID 19386479. Archived from the original (PDF) on 2021-03-03. Retrieved 2019-12-14.
- ^ Holbrook, Luke T. (1999-09-01). "The Phylogeny and Classification of Tapiromorph Perissodactyls (Mammalia)". Cladistics. 15 (3): 331–350. doi:10.1111/j.1096-0031.1999.tb00270.x. ISSN 1096-0031. PMID 34902952. S2CID 221584511.
- ^ Sánchez-Villagra, Marcelo R. (22 December 2012). "Why are There Fewer Marsupials than Placentals? On the Relevance of Geography and Physiology to Evolutionary Patterns of Mammalian Diversity and Disparity" (PDF). Journal of Mammalian Evolution. 20 (4): 279–290. doi:10.1007/s10914-012-9220-3. S2CID 18789008.