738 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Stibcursorial deep-bodied artiodadyls. — There are I similar ratios. These are the OUgocene Oreodon and 

 two types, ancient and modern, which have strikingly 1 the modern Sus. 



Measurements, in miUimeters, and ratios of limhs of subcursorial artiodadyls 



Cursorial heary-bodied artiodadyls. — These relatively 

 heavy-bodied animals were for the most part derived 

 from light-limbed and light-bodied cursorial and 

 subcursorial ancestors. This is positively known to 

 be true of the'ancestry of the camels. They therefore 

 are to be compared with the heavy-bodied cursorial 



Equidae as representing a retrogression from the high- 

 speed ratios of the ancestral light-bodied forms. The 

 excessively long limbs and high limb ratios of the 

 giraffe are doubtless an adaptation to the peculiar 

 feeding; habits. 



Measurements, in millimeters, and ratios of limbs of cursorial artiodadyls 



Meta- 



carpo- 



humeral 



ratio 



Plains-living : 



Camelus arabicus 



Bison bison 



Girafia camelopardalis 



Torest-living : Cervus megaceros. 



56 



60 



143 



103 



Graviportal sJiort-limbed digitigrades. — These ani- 

 mals are directly derived from ancestral mediportal 

 digitigrades through increasing weight of body and re- 

 duction in the length of the limbs. They are not 



short-footed but medium-footed, or mesatipodal. 

 Three of them (Teleoceras, Metamynodon, Hippopo- 

 tamus) are or probably were aquatic or amphibious. 



Measurements, in millimeters, and ratios of limhs of graviportal digitigrades 



Toxodon sp 



Teleoceras fossiger 



Metamynodon planifrons. 

 Hippopotamus amphibius 



Meta- 



carpo- 



humeral . 



ratio 



38 

 37 

 39 



38 



" Estimated. 



Graviportal long-limbed digitigrades. — The Oligo- 

 ■cene titanotheres are the only known quadrupeds of 

 this type. They are distinguished by being relatively 

 long-hmbed in contrast with the short-limbed group 

 just described and with the mediportal and graviportal 

 rhinoceroses. A striking fact is that the limb ratios 

 .are very similar to those in the low-bodied, short- 



limbed class above described. Thus the ratios remain 

 the same in low-bodied and high-bodied heavy forms 

 of moderate speed. It is noteworthy that the hind 

 limb of the titanotheres parallels that of the elephant 

 or rectigrade group and is quite unlike that of the 

 other graviportal digitigrades. 



