454 LAND MAMMALS IN THE WESTERN HEMISPHERE 



While -\Pantolambda 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 flesh-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 



