MAMMALIA 409 



horse family arose in the Lower Eocene of North America, and 

 Eura'sia. Its descent has been traced from a primitive five-toed 

 Ungulate. True pigs (Sus) are known from the Middle Eocene. 



The giraffes, found from the Pliocene to the present, were not 

 confined to Africa, but were present in Eurasia as well. The llamas 

 and camels were found on the North American continent in the 

 Upper Eocene. Later they migrated into South America, Asia, and 

 Africa. 



Order IX. Sirenia. — Aquatic with moderate-sized head, 

 depressed fish-like body, paddle-like pectoral limbs, pelvic limbs 

 absent, horizontal tail fin. No dorsal fin. Integument thick, 

 wrinkled and hairless. Snout inconspicuous, nostril openings 

 paired and dorsal; cervical vertebrae unfused, clavicle absent. 

 Fore legs pentadactyle, often with rudimentary nails; always a 

 flexible elbow. Brain comparatively small, convolutions ?wt highly 

 developed. Testes abdominal; teats are two in number and pectoral 

 in position. Uterus two-horned and the placenta non-deciduate 

 and zonary. 



The dugong is the only Old World Sirenian. It reaches a length 

 of fourteen feet, and was once so abundant off the coast of Queens- 

 land that a dugong fishery was established at Moreton Bay (Horna- 

 day). 



The manatee or sea cow reaches a length of twelve or thirteen 

 feet and a weight of twelve hundred pounds, superficially resembling 

 a seal. Its tail, a rounded disc, is a powerful propeller. The 

 Florida manatee reaches a length of about nine feet. Nearly ex- 

 terminated, a fine of $500 protected it till it is now on the increase. 

 The flesh of the Sirenia is considered a delicacy by some. Monks in 

 South America eat all aquatic mammals on fast days, as they con- 

 sider them fish. 



Stellers sea cow {Rhytina), the " Arctic sea cow" furnished food 

 for Captain Bering when his ship was wrecked on Bering Island in 

 1741. Steller, the naturalist of the Bering expedition, reported 

 their length as about twenty-five feet and weight as much as eight 

 thousand pounds. The species was exterminated in 1854. 



Fossil Relatives of the Sirenia. — The sea cows originated in the 

 Eocene of Egypt, and the West Indies, and were later found in 

 Europe and America. It is supposed that the sea cows and the 

 elephants may have been derived from a form occurring in the 

 Middle Eocene. 



