1 16 UNGULATA order vii 



Sciurinae, originating in North America, we have the Pseudosciurinae ; the 

 Theridomyinae, originally related to these ; the Hystricinae and Myoxinae ; and 

 the Cricetinae. The last subfamily has representatives in the North American 

 Oligocene, from which the Hesperomyinae are descended. The Castorinae 

 appear in Europe during this period. Still earlier we find the Ochotonidae in 

 Europe ; their origin, however, is still obscure. All of the above-mentioned 

 families, with the exception of Pseudosciurinae and Theridomyinae, which soon 

 become extinct, remain in this region throughout the entire Tertiary, and 

 some of them migrate also into Asia and Africa. The rather sparsely 

 represented Cricetinae give rise to the two subfamilies Mnrinae and Arvicolinae in 

 Europe. The former gradually migrate to all parts of the globe, and the latter 

 inhabit, for the most part, the northern part of Noi'th America and Eurasia. 



The Theridomyinae are rather important on account of their evolutionary 

 history. They become extinct in Europe after the Lower Miocene, it is true, 

 but attain a high degree of development slightly later in South America ; 

 they give rise not only to the Erethizontinae and Capromyinae but also to the 

 Octodontinae and Chinchillinae. The Issiodoromyinae, which can be traced back 

 to the Theridomyinae, in turn give rise to the Caviinae. The latter group 

 appears first in the Pyrotherium beds of Patagonia. Erethizontinae and 

 Octodontinae are found in the Colpodon beds, and are represented by many 

 genera and species in the Upper Miocene of Santa Cruz. Thus, this rodent 

 fauna is second in complexity only to that found in South America in the 

 early Tertiary, in the Pleistocene and in recent times. The recent rodent 

 fauna of South America differs from that of the Santa Cruz beds only in the 

 presence of the Leporidae and Hesperomyinae. Contrasted with the Hystricoidea, 

 which must have immigrated from Europe, these two families wandered from 

 North America. The Erethizontinae, however, migrated from South to North 

 America. 



Order VII. UNGULATA. ^ 



The Ungulates are distinguished by having a dentition adapted for 

 herbivorous, seldom for omnivorous diet, and extremities adapted exclusively 

 for terrestrial habits. The terminal phalanges are, accordingly, broad and 

 blunt, seldom angular or irregular, and with horny hoofs. 



The primitive ungulates, according to Cope, were pentadactyl and 

 plantigrade, very like the carnivores, with short, stout extremities. The 

 manus and pes passed through several stages of modification, as follows : 



1. The plantigrade foot became transformed, by means of the infrequent 

 use of the metapodials, into a semi-plantigrade condition. In this form the 

 end-phalanges and the metapodials, supported and strengthened by a muscular 

 pad, bore the full weight of the body. From this semi-plantigrade foot 

 developed, on the one hand, the unguligrade foot ; and on the other, the 

 digitigrade. In the former the metapodials are entirely lifted from the 



^ Cope, E. D., The classification of tlie ungulate Mammalia. Proc. Amer. Philos. Soc, 1882. — 

 Gregory, W. K., The orders of mammals. Bull. Amer. Mus. Nat. Hist., New York, 1910.— 

 Koiocdevsky, \V., Monographie der Gattung Anthracotherium. Palaeontographica, 1874, vol. 

 xxii. — Oshorn, U. F., Evolution of mammalian molar teeth. New York, 1907. — The evolution 

 of the ungulate foot. Trans. Amer. Philos. Soc, 1889, vol. xvi. — Riitimeyer, L., Beitriige zur 

 vergleichenden Odontographie der Huftiere. Verh. Naturf. Ges. Basel, 1863. — Schlosser, M., 

 Beitriige zur Stammesgeschichte der Huftiere. Morph. Jahrb., 1886. vol. xii. 



