192 F. B. LOOMIS ORIGIN OF SOUTH AMERICAN FAUNAS 



therium, Notocliaiihorus, Prototherium, Diadiaphorus, and Thaotherium, 

 the pseudo-horse.s. There was also a less progressive line, Portheosodon, 

 Theosodon, and Macrauchenia, the two lines making the litopternas. 

 These roughly parallel the l'*erissodactyls of North America and indicate 

 that, given similar material in similar environments, parallel evolutionary 

 lines result. 



Again, in the Notostylops beds there is a group of teeth, Pantostylops, 

 Trigonostylops, Albertgaudryi, etcetera, which resemble the teeth of 

 Amblypoda so strongly that Ameghino assigned them to this group, and 

 from them traced first a line through Astraponotus, Parastrapotherium, 

 Astrapothericulus to the aberrant Astrapotherium. It is a distinct line 

 of development similar to that leading to Uintatherium in North Amer- 

 ica, and the forms should be given either ordinal or subordinal rank, ac- 

 cording to the treatment given to other similar lines. The Homalodo- 

 theres, with their heavy build, broad feet, and cleft toes, run through 

 such forms as Asmodeus and in like manner represent a line of develop- 

 ment. All these forms are pretty clearly derived from condylarth stock 

 and should be grouped together. 



In regard to the typotheres and toxodonts, it seems to me they repre- 

 sent a separate group. The two lines are already distinct in Notostylops 

 time. One line runs through such forms as Notostylops, Rhynchippus, 

 Leontinia, Nesodon, and Toxodon, the toxodonts; the other includes 

 Notopithecus, Archseohyrax, Hegetotherium, Pachyrucos, and Typo- 

 therium, the typotheres. In the two groups the ground plan of the teeth 

 is the same. The feet of the typotheres are the less specialized, but nei- 

 ther advanced beyond the three-toed condition. Both early developed a 

 high degree of hypsodonty, and to my mind were grass-eaters : but at the 

 same time there is something unguessed about their habits, for they are 

 too slow and clumsy for prairie animals. The plan of their teeth could 

 well come from the Condylarth type, but they seem to have separated off 

 earlier than the litopternas, etcetera. 



There is left but Necrolestes, called by some an insectivore, close to the 

 Cape golden mole, at the same time compared to the marsupial mole, 

 Notoryctes. It may be an insectivore, but if so it is the only representa- 

 tive of the order found fossil in South America. The auditory bulla, 

 which would settle the question of its affinities, is lacking. Personally I 

 am inclined to think it is a specialized marsupial. 



From the above we can pretty confidently look to North America at the 

 beginning of the Eocene for the origin of all the South American mam- 

 mals, rodents excepted, and to the isolation of the continent we can at- 

 tribute the specialization of their development. The only group which 

 has suggested the need of a land bridge is the hystricomorph rodents 



