146 THE AGE OF MAMMALS 



edge, of several families, including the artiodactyl anoplotheres (Anoplothe- 

 rium) and csenotheres, of the true dogs or Canidse (Cynodictis), and of two 

 previously unkno^\Tl families of rodents, Theriodomyidse ^ and Myoxidai 

 (dormice). More distinctive is the appearance here of diminutive opossums 

 (Didelphyidae, Peratherium) , either by migration from North America, or 

 as residents which have not been discovered in older formations. 



Mammalian Succession 



Cuvier's views restated. — It is interesting to describe the adaptive radia- 

 tion of the gypse fauna so far as possible in the language of Cuvier.^ The 

 chief animals which he discovered were the palseotheres, which reached their 

 cUmax at this time, the aberrant artiodactyl anoplotheres, the anthraco- 

 theres, Choeropotami, and the lemuroid Adapis. The palseotheres were brows- 

 ers, forest-living animals, resembling tapirs (P. medium) in the general 

 form of the body and head, particularly in the shortness of the bones of 

 the nose, which indicate that, like the tapir, they had a short, prehensile 

 proboscis, or upper lip; their grinding teeth are crested like those of the 

 forest-living horses of the Miocene of North America (Hypohippus) or of 

 the short-crowned lophoselenodont type. Their resemblance to the forest- 

 living horses is also shown in the presence of three digits on both fore and 

 hind feet. "Our gypsum quarries," observed Cuvier, "are crowded with 

 these animals." The adaptive radiations of the palseotheres are observed 

 first in their size, and second in the variations of the structure of their feet. 

 The largest palaeothere (P. magnum) was of the size of a horse; another 

 species (P. medium) resembles the boar in size and is distinguished by long, 

 narrow feet; a third species (P. crassum) is distinguished by its broader 

 feet, and a fourth (P. latum) by feet still larger but with shorter 

 digits; a fifth species (P. curtum) only attained the size of a sheep, but its 

 feet are still larger and shorter in proportion. The sixth species (P. minus), 

 which was attributed to Palceotherium by Cuvier, has longer legs and is of a 

 lighter build than the others; it is distinguished by very slender feet, the 

 lateral toes of which are shorter than the median, and is now known under 

 another name (Plagiolophus minus). It is famous as having been selected 

 by Huxley as one of the early ancestors of the horse; we now perceive 

 that it was parallel with, rather than ancestral to, the early horses. Cuvier 

 described the anoplothere as of the height of the wild boar, with much- 

 spreading feet and a very long and thick tail, so that as a whole it had nearly 

 the proportions of an otter but with longer legs; it is probable, he said, 

 that it swam well and frequented the lagoons. In widest contrast to these 

 forest and swamp-living forms were the xiphodonts, which, as restored by 



' Schlosser regards the theriodomyids as primitive hystricomorph or porcupine-like 

 rodents. 



^ Cuvier, G., Discoura sur les Revolutions de la Surface du Globe, et sur les Changemens 

 qu'elles ont Produits dans le R6gne Animal. Paris and Amsterdam, 1826. 



