454 LAND MAMMALS IN THE WESTERN HEMISPHERE 



While ]Pantolamhda was an undoubted ungulate and a 

 member of the fAmblypoda, there were many structural 

 features in its skeleton which point to a relationship with the 

 primitive fiesh-eaters. In the lower stage of the Paleocene, 

 the Puerco, the genus ^Periptychus would seem to be the most 

 ancient known member of the order, but it is still very im- 

 perfectly understood. 



In the mode of evolution of the fAmblypoda, so far as that 

 is recorded by the fossils, there is much to recall the develop- 

 ment of the Proboscidea, though the story began and ended 

 at far earlier dates and may be traced back to a much more 

 primitive stage. 



(1) There was a rapid increase of stature, especially of 

 bulk, in the fcoryphodonts, but decidedly more gradual 

 in the fuintatheres, which eventually attained a far larger 

 size. 



(2) The upper incisors were suppressed and the canines 

 grew into formidable tusks, at first straight, then the superior 

 one, enlarging still farther, acquired a curved, scimitar-like 

 shape, while the inferior one dwindled and became functionally 

 one of the incisors. 



(3) The grinding teeth remained low-crowned throughout, 

 but acquired a more complex pattern, and the premolars became 

 almost like the molars. 



(4) The skull underwent a most remarkable transformation. 

 Beginning with a form that might have belonged to almost 

 any of the ancient mammals, hoofed or clawed, having very 

 prominent sagittal and occipital crests, long cranium and 

 short face, it became in ^Coryphodon flat-roofed, with mod- 

 erately elongated face, while in the fuintatheres the top of the 

 cranium gradually took on a deeply concave basin-shape and, 

 with equal gradualness, three pairs of horn-like protuberances ; 

 the lower jaw developed a great bony flange for the protection 

 of the upper tusks. These peculiarities grew more and more 



