UNGULATA (Lat. nom. pl., having claws or hoofs, from angula, claw, hoof, diminutive of unguis, Clk. iier,f, onyx, nail, veined gem, onyx, thickening in the cornea of the eye. 01r. inga, An order of mammals, including thin elephants, hyra colds, hoofed animals, and related forms of the past; the ungu lates. The earliest known forms from the basal Eocene have many resemblances to the Creodonta or prim itive Carnivora in the small brain, the denti tion, the eomparatively short legs and long heavy tail, and the pentadaetyl font. However, it may he that the resemblance to the ereodonts is only a parallelism, in that both these groups have re tained primitive characters inherited probably from the still earlier lnseetivora Primitiva. from \Cilia it seems likely both these groups have sprung.
The tendency of the group is very early shown in the development of a true herbivorous type of tooth, and a type of limb adapted to running. The oldest forms have the foot plantigrade or nearly so, but the change through the semi-planti grade and digitigrade to the unguligrade foot, with only the terminal phalanx resting on the ground, is rapid. Also in the earliest forms all the five digits were about equally functional. but began very early a specialization in two diree tions—the niesaxonie type with the axis of the foot in the third or middle digit. as in the penis sodactyl or odd-toed forms, and the paraxonie type with the axis between the third and fourth digits as in the artiodactyl or even-toed forms. The connecting links between the great groups of ungulates have not yet been well established. 'lice Condylarthra, represented by the Lover Eocene Phenacodus, seem to be the mo,-t primi tive, and it is the general opinion that the other groups have descended from some very early con dylarth. The ungulates undoubtedly began to radiate in the Cretaceous, for, though none have yet been recorded for that formation, there are two well-marked groups, the Condylarthra and the Amblypoila, in existenee at the very base of the Ficteene; the Amblypoda specialized into the clumsy and bizarre nintatheres (see UmTArnic mum) and both groups became extinct before the end of the Eocene period. The radiation
of ungulates continues through the Eocene, and during this period all the great groups become well differentiated. Of the Perissodaetyla the Palwotheriidie, Equithe, Tapiridic, Lophiodonti dx, and lEyracodontidie appear in the Lower Eocene, the Titanotheridat and Amynodontidie in the Aliddle Eocene, autd the Rhinocerotidir in the Upper Eocene. The great expansion of this group is in the Upper Eocene and Oligocene. The Proboseidea and Ilyraeoidea probably arose, at the latest. in the Upper Eocene. Besides these forms, which were common to most of North America and Eurasia, there arose in South America an ungulate fauna found nowhere else, consisting of the three groups Litopterna, Typo theria, and Toxodontia. These seem to be en tirely unrelated to other ungulates except pos to the Condylarthra. They flourished in the and Pliocene and became extinet in the Pleistocene.
The ungulates are from the standpoint of hu man economy the most important, and have been the chief support of mankind since he attained supremacy, furnishing him with most of the food, clothing, and working assistance which he derives from animals. The four existing suborders are the Hyracoidea, Proboscidea, Artiodactyla, and Perissodaetyla. See 11 YHA X ; ELEPHANT; PRO ROSCIDEA ; RUMINANT; BOVID_E ; HORSE; RHI NOCEROS; and the names of allied groups and species. Consult: Beddard, Manintalia (London, 1902) ; Woodward, Vertebrate Pubrontology (New York, 1898) ; and the recent literature therein cited.