CLASS MAMMALIA 685 



ancestors are not known, but there are many wild sheep of 

 the same genus (Ovis) from which they may have originated. 

 Goats have also been domesticated since the earliest times, 

 and their wild relatives are abundant in many parts of the 

 world. 



The domesticated pigs are descended from the European wild 

 boar, Sus scrofa, and the Indian wild boar, Sus cristatus. 



The common house cat has a complicated ancestral history. 

 Its remote ancestor was probably the Egyptian cat, Felis libyca, 

 from which the Mediterranean cat, F. mediterranea, the wild- 

 cat, F. catus, the jungle cat, F. chaus, the steppe cat, F. caudata, 

 and the Indian desert cat, F. ornata, descended. The European 

 and American domesticated cats were derived either from the 

 Egyptian cat or the Mediterranean cat, which soon became 

 crossed with the wildcat. The spotted Indian domesticated 

 cats are derived from the Indian desert cat. A number of crosses 

 have been made between the various wild and domesticated cats, 

 resulting in a large variety of mixed breeds. 



g. Fossil Mammals 



Fourteen of the thirty-two orders of mammals are known only 

 from fossil forms (H. F. Osborn). The earliest known remains 

 of mammals are from the Triassic period, a period which began 

 about ten million years ago (see Table XVII). The genera 

 Dromatherium and Micronodon, taken in the Upper Triassic of 

 North America, have been referred tentatively to the first order 

 of mammals, the PROTODONTA. The mammals of both the 

 Triassic and Jurassic periods were small. A number of genera 

 of marsupials (MULTITUBERCULATA) and the lowest placental 

 mammals, the TRITUBERCULATA or Mesozoic insectivores, are 

 referred to the Jurassic period. In Cretaceous times the evolu- 

 tion of the existing orders of placental mammals took place. 

 There are, however, very few remains; the genera Ptilodus and 

 Menisccessus are marsupials (MULTITUBERCULATA) from the 

 Upper Cretaceous of North America, 



