466 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



without notable change to the Pliocene, but there it was in 

 association with the last of a curious phylum, the genus 

 ^Trigodon (Fig. 138, p. 263), as yet known only from the skull. 

 In these animals a very prominent bony knob or boss on the 

 forehead clearly demonstrates the former presence of a large, 

 rhinoceros-like, frontal horn. But very few of the indigenous 

 South American ungulates possessed horns, or horn-like pro- 

 tuberances of the skull, and all of these so far discovered 



Fig. 235. — Skull of ^Toxodon, Pampean formation, the upper molars much broken. 



La Plata Museum. 



belonged to the suborder fToxodonta. ]Trigodon was, from 

 present knowledge, the only horned creature of its time and 

 region, for the deer and antelopes which had probably arrived 

 in South America had not advanced so far south as Argentina. 

 Another very peculiar feature of this genus was that the lower 

 incisors were present in uneven number, two on each side 

 and one in the middle. Nothing has been found of the 

 skeleton, but it was doubtless that of a smaller and somewhat 

 lighter \Toxodon. 



