PREHISTORIC ANIMALS 



1-33 



suborders, and families, which have become extinct in one or 

 another of the Tertiary periods. 



The most interesting representatives of the Edentata occur 

 in the Pleistocene of North and South America, and at that 

 time this order reached its greatest development ; but even in 

 the Miocene some gigantic species have been found in Europe, 

 although there are no Edentata on that continent to-day. The 

 Sirenia are represented by two families, one now extinct, the 

 other that of the dugongs, of which specimens have been found 

 in France and California. Cetacea are found throughout the 

 Tertiary. The toothless, or whalebone, whales are found in the 

 Miocene and the 

 Pliocene. The 

 genus Delphinus, 

 which includes 

 the common dol- 

 phins, dates back 

 to the Miocene. 

 Some interesting 

 extinct genera 

 (Fig. 412) have 

 been found, such 

 as Zeuglodon, 

 which occurs throughout the Tertiary in Europe, Egypt, and 

 North America ; one of the largest specimens is from the 

 Eocene of the United States, having a length of about twenty- 

 one meters. 



The Ungulata are represented by an immense number of 

 fossil species and genera ; many families have become extinct. 

 One of the most interesting features of the fossil Perissodactyla 

 is the progressive reduction of the lateral digits as we pass from 

 the earlier to the more recent genera. The family Equidae, 

 represented to-day by the horse, the ass, and the zebra, is a 

 good example. The little Eohippus, about the size of a fox, of 

 the Lower Eocene beds of New Mexico, had five digits on each 

 of its anteror appendages, three on the posterior; the Orohip- 

 pus, of slightly higher beds, had four digits on each fore leg and 

 three on the hind legs. In the Lower Miocene beds we find the 

 genus Mesohippus, with three digits on each foot ; toward the 



2 F 



FlG. 412. Squalodon, an extinct genus of whales with heterodont 

 dentition, which appeared in the Miocene; three of the molar 

 teeth from the lower jaw. (After Flower, from Parker and 

 Haswell's Text-book.) 



