South Dakota School of Mines 75 



"many, and a few crocodiles, lizards, and birds eggs, all of the 

 fossil remains of the vertebrates thus far found within the area 

 belong to the great class "Mammalia". The term "Mammalia" 

 includes all hair-clad, vertebrated animals, the females of which 

 are provided with glands for secreting milk for the early 

 nourishment of the offspring. They are the highest of the 

 vertebrates, possessing that happy combination of anatomical 

 and physiological simplicity and complexity tending toward 

 highest efficiency as organisms. They are not only the most 

 important animals of today, but they have been the rulers of 

 the animal world since early Tertiary time. Continuing back in 

 geological history with ever increasing simplicity toward a 

 •generalized, omnivorous, allotherian ancestry they may be 

 traced with certainty 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 two great sub- 

 classes of the Mammalia may be recognized, namely, the Proto- 

 theria or primitive mammals and the Eutheria or perfect mam- 

 mals. The Prototherian mammals are restricted to very 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. The Proto- 

 theria are not represented in the Black Hills region either living 

 •or fossil, hence need no further consideration in this paper. 



The Eutheria unlike the Prototheria include a vast as- 

 semblage of forms of all sorts of perfection of development 

 from the lowly marsupials or pouch-bearing animals (sometimes 

 classed as Metatheria) to man. These are grouped somewhat 

 differently by different authors but all of the fossil forms 

 obtained from the region under discussion in this paper fall 

 naturally into four main divisions, namely, the Insectivora, the 

 Carnivora, the Rodentia, and the Ungulata (hoofed mammals), 

 the Ungulata (Herbivora) being represented by two orders, 

 the Perissodactyla and the Artiodactyla.* 



The Insectivores include moles, hedgehogs, shrews and 

 other small animals of antiquated structure. They are gener- 



*The Proboscidea are represented by two broken teeth found in 1906 in 

 the lower part of the Upper Harrison beds near Agate, Sioux County, 

 Nebraska. These were described by Mr. Harold J. Cook in the Am. Journ. 

 Sci. vol. 28, 1909, pp. 183-184 under the name GomphotheriurK conodon. 



