GENERAL ZOOLOGY 



Fig. 18.29. Reconstruction of a mammal-like reptile, Cynonnathus, which li\ed in late Triassic 

 time and represents a reptilian type believed to have been ancestral to mammals. (Photograph 

 courtesy American Museum of Natural History.) 



Order Primates: lemurs, monkeys, apes, and man. 



Order Carnivora: cats, lions, dogs, wolves, foxes, bears, raccoons, seals, sea 



lions, walruses, and many others. 

 Order Perissodactyia: odd-toed hoofed mammals, such as horses, zebras, tapirs, 



and rhinoceroses. 

 Order Artiodactyla: even-toed hoofed mammals, such as swine, hippopotami, 



camels, llamas, deer, cattle, and many others. 

 Order Cetacea: whales, dolphins, and porpoises. 

 Order Proboscidea: elephants. 

 Order Rodentia: rodents, such as squirrels, rats, mice, beavers, porcupines, 



and many others. 

 Order Edentata: sloths, armadillos, and anteaters. 



The three subclasses Prototheria, Metatheria, and Eutheria, represented by 

 the duckbill, the opossum, and the more common placental mammals, respec- 

 tively, as well as the nature of mammalian embryonic development, should be 

 kept in mind through the account that follows. The fossil record gives clear 

 evidence of mammalian origins. Reptiles along the line leading to the Mam- 

 malia are found in the Carboniferous and Permian of Texas. Forms even 

 more like mammals occur in the Permian and Triassic of South Africa, where 



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