EVOLUTION OP THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHEEES 



587 



This deficiency of material renders all the more 

 valuable the broader investigation and comparison 

 with other Perissodactyla which will be presented in 

 Chapter X. The new and precise system of compara- 

 tive measurements of the limbs establishes certain 



subphyla (genera). Members of these six or more 

 phyla were separated by the weight, shape, and pro- 

 portions of the body, feet, and limbs, such separation 

 being indicative of a considerable range of size, speed, 

 and migrating ability in search of food. This demon- 



FiGUEE 484. — The phyla of Eocene titanotheres, as represented by the manus 

 A, Lambdotheriinae (,Lambdotherium); B, Eotitanopinae (Eotitanops); C, Palaeosyopinae (Limnohyops); D, Palaeosyopinae iPalaeosyops); 

 E, Manteoceratinae (.Manteoceras)] F, T>o\iehorhininae (Mesatirhinu^). One-third natural size. 



laws of limb adaptation and enables us to estimate 

 fairly closely the speed and weight-bearing powers of 

 the various kinds of titanotheres. 



1. Existence of many pliyla. — The chief conclusions 

 drawn from the limb bones of titanotheres, moreover, 

 confirm those drawn from the skull — namely, the exist- 

 ence of six or more distinct phyla in the lower Oligo- 

 cene. That there were six or more contemporaneous 

 but more or less independent phyla, characterized by 

 differences of limb structure and modes of locomotion, 

 is clearly shown, as well as the fact that these include 

 two main phyla each of which embraces at least three 



strates the existence of two early radiations (sub- 

 families) and of subsequent branch radiations (genera). 



FiQUKE 485. — Progressive broadening of the magnum 



in Eocene titanotheres 

 A, Eotitanops (subcursorial) ; B, Mesaiirkinus (mediportal) ; C, Lim- 



nohyops (mediportal); D, Palaeosyops (subgraviportal) . One-balf 



natural size. 



2. Adaptive characters superposed on ancestral. — • 

 Similar limb and foot proportions, like similar skull 



