76 THE WHITE RIVER BADLANDS 



tainty to Triassic time. Since their beginning multitudinous 

 changes have taken place in the structure and activity of 

 the many species that have originated, developed and died 

 and, as a result, the expression of relationship must often 

 be indefinite or uncertain. 



Following the custom of many authors three main 

 subclasses of the Mammalia may be recognized, namely, the 

 Prototheria or primitive mammals, the Metatheria or 

 pouched mammals and the Eutheria or perfect mammals. 



The Prototherian mammals are restricted to a few 

 simple forms such as the Echidna (Australian Ant Eater) 

 and the Ornithorynchus (Duck-billed Platypus) which lay 

 large yolked eggs much after the fashion of reptiles and 

 birds. They are not represented in the White River bad- 

 lands either living or fossil, hence need no further consider- 

 ation here. 



The Metatheria are those intermediate, marsupial 

 mammals which, having only a rudimentary or primitive 

 placental structure, bring forth their young in a very im- 

 mature state and carry them for a considerable time in a 

 pouch provided for the purpose. The opossum, the kanga- 

 roo and the Tasmanian "wolf" are well known representa- 

 tives. Like the Prototheria the Metatheria are not found 

 in the White River badlands. 



The Eutheria include a vast assemblage of forms of all 

 sorts of perfection of development from lowly primitive 

 creatures to man. These are grouped somewhat differently 

 by different authors but all of the fossil forms obtained 

 from the region under discussion fall naturally into four 

 main divisions, namely, the Insectivora (insect eaters) the 

 Carnivora (flesh eaters), the Rodentia (gnawers), and the 

 Ungulata (hoofed mammals), the Ungulata (Herbivora) 

 being represented by two orders, the Perissodactyla (e^ea^ 

 toed mammals) and the Artiodactyla (odd-toed mammals). 



The Insectivores include moles, hedgehogs, shrews and 

 other small animals of antiquated structure. They are 

 generally plantigrade (walking upon the sole of the foot), 

 the snout is often prolonged into a short proboscis, and 

 their chief food is insects. The Carnivores include animals 

 whose chief food is flesh. They may be terrestrial, arboreal, 





