TERTIARY VERTEBRATE FOSSILS. 



521 



As the Eocene is not represented, the first noteworthy fauna above 

 the Ceratops beds is that in which the remains of the Brontotheriidse are 

 so abundant. These huge ungulates belong to the perissodactyl, or odd- 

 toed, mammals, and they were the largest land animals during early 



Fm. 87. — Upper molar tooth of Cimolomyi digona Marsh. 



Fig. 88.— Third or fourth lower premolar of Halodon serratua Marsh. 



Fig. 89 Upper molar of Allacodon lentus Marsh. 



Fig. 90. — Low r jaw of Tdacodon praata/na Marsh. 



Fm. 91. — Upper cutting premolar of Oraeodon anctps Marsh 



Fn;. 92.— Premolar of Btagodon vdlidva Marsh, 

 a, natural size; o-s, twice.na1 aral size, exoepl fig. 89, which is three times natural size. 

 /<, outer view; <\ end view; d, inner view; e, top view. 



Miocene time. The characteristic genera of this family found on the 

 plains east of the Denver Basin, or farther north along the South Platte 

 River, are Brontotherium, Brontops, Megacerops, Symborodon, and 

 Titanops, with others less known. The skulls of two of these genera, 



