HISTORY OF THE JLITOPTERNA 493 



like that of any existing hoofed animal. The form and size 

 of the ears and the character of the hairy coat are, of course, 

 conjectural. 



In the later Pliocene the family was represented by forms 

 which differed so little from the Pampean \Macrauchenia as 

 to call for no particular notice, but in the presumably lower 

 Pliocene of the Parana stage, occurred several genera, all un- 

 fortunately but imperfectly known, which are of interest as 

 being less specialized than 'fMacrauchenia and as showing 

 the way in which some of the peculiarities of the latter were 

 acquired. In jScalibririitherium, which may be taken as an 

 example of these genera, the teeth were brachyodont ; the 

 upper molars were rather less complex than those of fikfac- 

 rauchenia, while the lower molars had the pillar in the con- 

 cavity of the posterior crescent, which the Pampean genus 

 retained only in the milk-teeth. As we have repeatedly 

 found, the milk-dentition is often conservative and retains 

 primitive or archaic features which have been lost in the per- 

 manent teeth, and ^Macrauchenia is another illustration of the 

 same principle. In the skull of ^Scalibrinitherium the nasal 

 bones, though very short, had not suffered such extreme ab- 

 breviation as in the succeeding genus, the nasal opening was 

 farther forward and the maxillaries united in the superior 

 median line for only a short distance, while the premaxillaries 

 were fused together for their whole length. The orbit had not 

 been shifted entirely behind the teeth, but was above the third 

 upper molar. 



Next in the ascending series, to use the genealogist's term, 

 came the genus ^Theosodon of the Santa Cruz, of which al- 

 most all the skeletal parts are known and thus make possible 

 a full comparison with fMacrauchenia, which assuredly was 

 its direct descendant. In view of the great lapse of time in- 

 volved, the differences between the two genera were less than 

 might have been expected, though the more ancient animal 

 was in all respects the more primitive. \Theosodon was, in 



