610 THE POPULAR SCIENCE MONTHLY. 



lemurs. Both of the two species known are small, not probably ex- 

 ceeding a gray squirrel in size. Only the skulls and jaws are known 

 (Fig. 2). 



But the Condylarthra prove to be the ancestors of a still greater 

 population of descendants. We have traced all forms of grinding 

 teeth up to a pattern which consists of four tubercles or cones arranged 

 within a square. But it has been possible to show that one of the four 

 tubercles appeared after the other three, as an addition to them, so 

 that the earliest form, of molar or grinding tooth was tritubercular, 

 and that the quadritubercular was an outgrowth from it. Now, one 

 of the three families of the Condylarthra has tritubercular molars, and 

 there is little doubt that it was the ancestor of the two other families. 

 The principal genus of this family is called Periptychus. From this 

 family came an order of hoofed mammals, which never rose to the 

 possession of four tubercular grinders, although the crowns became 

 crested by the modification of the three which they possess. This or- 

 der, the Amblypoda, had a short life in geological time, and did not 

 grow in the dimensions of the brain, but developed huge skeletons 

 with skulls that sprouted into horns and strange processes. 



The Condylarthra with three tubercles are probably also the ances- 

 tors of the carnivorous orders. The lions, tigers, wolves, and bears of 

 to-day can be shown to be descendants of animals absolutely interme- 

 diate between themselves and the animals just mentioned. These 

 half -carnivores, or Creodonta, have, like the ancient hoofed mam- 

 mals, more numerous teeth than their modern representatives, and dif- 

 fer from the true carnivora in just the ways, in limbs and feet, that 

 we have seen that the ancient hoofed mammals differ from their mod- 

 ern descendants. Creodonta were not such dangerous animals as the 

 carnivora, with some possible exceptions, because, although they were 

 as large, they generally had shorter legs, less acute claws, and smaller 

 and more simple brains. 



This genealogy, it will be seen, does not show us the ancestors of 

 the Condylarthra. This remains for future discovery. It is, however, 

 probable that they will be found in the earlier geological periods, 

 among some of the marsupial mammals only known thus far from the 

 jaws and teeth. It must also be noted that a number of these ances- 

 tral groups are represented in the existing fauna by a few genera. Of 

 the Condylarthra, a near relative exists in the Hyrax, or cony, which 

 now inhabits Africa and Western Asia. Of the Creodonta, several 

 genera exist in Madagascar, West Africa, and the northern hemi- 

 sphere. The mastodons are late representatives of an ancient type, 

 and their phylogeny has not yet been fully made out. But they cer- 

 tainly also came from the Condylarthra. 



There is a remarkable likeness between the history of the develop- 

 ment of the reptiles and that of the higher mammals, in one respect, 

 and that is, that they have apparently all been derived from a single 



