500 LAND MAMMALS IN THE WESTERN HEMISPHERE 



ture of these extraordinary animals. Not that this remarkable 

 character was due to grotesque proportions ; on the contrary, 

 they looked far more like the ordinary ungulates of the northern 

 hemisphere than did any of their South American contempo- 

 raries ; it is precisely this resemblance that is so notable. 



In Santa Cruz times the family was represented by a large 

 number of species, which have been grouped in four or five gen- 

 era, which differed sufficiently to require generic separation, yet 

 were closely similar. In all of them the dental formula was : 

 i|, cf, p I, m|, X2 =36. Except in one genus {^Thoathe- 

 rium) a pair of small tusks was formed by the enlargement of 

 the second upper and third lower incisors, as in the ftoxodonts, 

 but the first upper and lower and the third upper incisors, which 

 were retained in the ftoxodonts, were lost in this family, as 

 was also the upper canine, and the lower canine was very small, 

 of no functional use. The teeth were brachyodont and, except 

 the small tusks, displayed no tendency at any time toward the 

 acquisition of high crowns. The premolars were less complex 

 than the molars, though the last one approximated the molar- 

 pattern. The upper molars had two crescentic outer cusps, 

 meeting in a vertical ridge and together forming the outer wall ; 

 the transverse crests were imperfect, especially the hinder one 

 which was often merely the intermediate cuspule, and did not 

 fuse with the external wall. The lower molars had the two 

 crescents, one behind the other, which recur in the fmacrau- 

 chenids, all the suborders of the fToxodontia, except the 

 fPyrotheria, and other South American ungulates, but the 

 pillar in the posterior crescent, which was so characteristic of 

 the groups named, was reduced to very small proportions and 

 sometimes suppressed altogether. It should be noted, how- 

 ever, that this was the loss of an element which was formerly 

 present. 



The skull had a long cranium and rather short face, with 

 long, high sagittal crest. The neck was short, the odontoid 

 process of the axis peg-shaped, and the canal for the vertebral 



