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Camelidae (camels; order Artiodactyla, infra-order Tylopoda) A family that includes the dromedary (Camelus dromedarius), Bactrian camel (C. boctrianus), llama (Lama glama), guanaco (L. guanicoe), and vicuña (L. vicugna). The dromedary is known only as a domestic animal; the Bactrian camel and guanaco have domestic forms (the domestic guanaco is called the llama). Another domestic camelid, the alpaca of the Andes, may be descended either from the guanaco or from a guanaco X vicuña hybrid. Camelids are ruminants in which the stomach has three chambers. Horns and tusks are absent. Hoofs, present in earlier forms, have been replaced by wide pads on the two digits of each foot. The gait is swaying, as fore and hind legs of each side move together. There is a vacuity between the lachrymal and nasal bones. Camelids appear first as fossils in N. American rocks of Upper Eocene age. Until nearly the end of the Tertiary they were almost exclusively N. American, but in the Pliocene they entered S. America and Asia and then spread into Africa. The late-Tertiary American forms included a ‘gazelle camel’ and ‘giraffe camels’. Camels became extinct in N. America toward the close of the Pleistocene. Today Camelus species are native to the Old World, where they are nearly extinct in the wild, and Lama species to New World. There are two genera, with four wild species.