THE MIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 285 



lions,' belong to a family now extinct in North America, but represented 

 in Chili, in Persia, and abundantly in Africa. Two species of the horse fly. 

 (Tabanus) are also found here, quite close to living forms. It is interesting 

 to note that while the Equidte have undergone generic changes since Miocene 

 times, their tormentors have remained not only generically the same, but 

 have changed little specifically.' The now extinct element in the insect 

 fauna includes certain plant lice, dragon flies, and cicadas. The Neo- 

 tropical or South American element, if there be any, must be slight. 



"From consideration of all the evidence," continues the same writer, 

 *'I conclude that the climate of Florissant at the time the shales were de- 

 posited was warm and moist, but in no sense tropical, the flora including a 

 hilly and lake border element. The altitude was not much less than it is 

 to-day (8,000 feet), but under the prevailing climatic conditions there were 

 no heavy wnnter snows. There is apparently no reason why these moist 

 mountain side conditions of the Florissant Lake should not have been 

 contemporaneous with the presence of arid conditions in Texas, Kansas, 

 and the great plains generally." * 



The horse flies of Florissant are especially interesting in connection 

 with the epidemic theory of extinction of some of the American mammals, 

 suggested by Osborn - and others. The deadly nature of the tse-tse fly 

 (Glossina) in Africa is well known. In Algeria the tabanids also transport 

 a trypanosome disease of the dromedary. It seems possible, therefore, that 

 both these flies may have been instrumental in carrying diseases to the 

 Mammalia.^ 



Lower Miocene 



Merycochoerus Zone 



Geologic distribution. — As described above on p. 279, the geographic 

 area in which these mammals are known is identical with that of the close 

 of the Oligocene because it is revealed in a continuation of the upper por- 

 tions of the Upper Oligocene, Arikaree, Harrison, and Rosebud Formations 

 of western Nebraska and South Dakota, also farther west around the 

 base of Laramie Peak, and to the south in the uppermost Martin Canon 

 of Colorado. Our knowledge is again due chiefly to the comparatively 

 recent explorations and studies of Peterson, Matthew, Cook, and Thomson. 



There is no foreign invasion. The mammal fauna is entirely American, 

 that is, derived from American Oligocene ancestors. A possible exception 

 is indicated by a portion of two teeth which remotely resemble those of 

 one of the primitive mastodons; we await further evidence on this point.* 



' Cockerell, Letter to the author, March, 1908. 



^ Osborn, H. F., The Causes of Extinction of Mammalia. A>ner. Natural., Vol. XL, 

 no. 479, 1906, pp. 769-795, no. 480, pp. 829-859. 



' Cockerell, Letter to the author, Jan. 9, 1909. 



* Cook, Harold ,J., A New Proboscidean [Gomphotherium conodon] from the Lower Miocene 

 of Nebraska. Amcr. Jour. Sci., Vol. XXVIII, Aug., 1909, pp. 183-184. 



