THE EOCENE PERIOD. 239 



that they may have extended farther back than the record indicates. 

 Their derivation is not yet determined. 



The primitive insectivores. — Most of the present families of insec- 

 tivores can be traced back to the Eocene. They retain even to this 

 day many of their primitive characters, agreeing with the creodonts in 

 their low type of brain and in some skeletal features. They are the 

 least altered of the great branches, and have been thought to most 

 nearly represent the character and habits of the primitive placentals, 

 but this remains an open question. 



The primates (Quadrumana). — Of the higher order of the primates, 

 the apes, no traces have yet been found in the Eocene deposits, the 

 earliest apes appearing about the middle of the Miocene. Of the lower 

 division, the lemuroids, representatives appeared in the Wasatch in 

 America and in a similar horizon in Europe, a distribution which is the 

 more notable as the lemurs are now confined to Madagascar and to 

 portions of Africa and southern Asia. The progress of investigation is 

 gradually filling up the gap between the lemuroids and the apes, and 

 there is now little doubt that the apes are descendants of the early 

 lemuroids. The latter show many affinities to the insectivores, and were 

 possibly derived from them. The Anaptoniorphas from the Wasatch of 

 Wyoming had large cerebral hemispheres of the type characteristic 

 of the primates. This must have contrasted strongly with the small 

 smooth brains of the contemporaneous creodonts and condylarths and 

 their derivatives. 



The mammals go down to sea. — Just as the land reptiles of Meso- 

 zoic times took to the sea by choice or by necessity, so did the mammals 

 in Cenozoic times, and thus arose the cetaceans (whales, dolphins, por- 

 poises), the sirenians (manatees, dugongs), and the pinnipeds (seals, sea- 

 lions). Some suggestion of the possible origin of the last is found in 

 Patriofelis, but the source of the cetaceans and sirenians is quite uncer- 

 tain. The latter have not yet been found in the Eocene deposits, but 

 the primitive cetaceans had representatives in the Zeuglodons, whale- 

 like animals of great length, whose limbs had become fully adapted to 

 an aquatic life, but whose dentition remained that of land animals. 

 While widely distributed, their preferred habitat seems to have been the 

 southern part of the Atlantic coast of the United States. In a certain dis- 

 trict in Alabama the vertebras were originally so abundant as to attract 

 much popular attention and call forth legends of divers catastrophes. 



