xxx. 7 CHALICOTHERES 731 



out, genera and perhaps even subfamilies have probably been created 

 on a basis of differences that may be only sexual or individual. 



7. *Chalicotheres (= *Ancylopoda) 



One remarkable side-line of perissodactyl evolution, while becoming 

 large and horse-like in some ways, acquired structures resembling 

 claws instead of hoofs (*Moropus, Fig. 485). These chalicotheres, all 

 rather alike, existed from the Eocene to the Pleistocene and were 

 therefore a successful group. The terminal phalanges of the three toes 

 of each foot were cleft and undoubtedly carried a nail or claw of some 



Fig. 485. Feet of a chalicothere. (After Romer, Vertebrate 

 Paleontology, University of Chicago Press.) 



sort, though not necessarily one like that of true unguiculates. There 

 is no doubt that in a sense this is a case of reversal of evolution, but 

 we cannot assert much about its possible genetic implications unless 

 we can find details of the nails. 



When chalicothere digits were first discovered in 1823 Cuvier 

 applied his 'law of correlation' and suggested that this was the remains 

 of an ant-eater, 'un Pangolin gigantesque', while teeth and other 

 bones found near by he referred to an ungulate. It was only when 

 skeletons were found in such a position that the association of the 

 bones could not be denied that the danger of this attempt to apply 

 deductive principles in biology was exposed. The other parts of the 

 skeleton are unambiguously perissodactyl (Fig. 479), the teeth rather 

 like those of brontotheres. There may have been a short proboscis. 

 The neck vertebrae of some forms show very strong zygapophyses, 

 and it has been suggested that the snout and claws were used for 

 digging for roots or water. It is more probable that the chalicotheres 

 reared up on their hind-legs and used the claws to cling to tree-trunks 

 while reaching for leaves with their flexible necks, or perhaps to drag 

 down branches. Like the toxodont *Homalodotherinm they had long 

 front legs and large ischia. Moreover, their remains are found in 



