734 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Groups of types of quadrupeds adapted to different speeds and paces 



Type of locomotion and speed 



Type of limb and toot structure 



Examples 



1. Ambulatorj- : Small, primitive, low- 



bodied animals, which walk, shuffle, 

 or run clumsily. 



2. Mediportal : Speed and pace of inter- 



mediate type, tending to become 

 graviportal. 



3. Graviportal : Gigantic, massive animals, 



which swing the limbs ponderously 

 in a walk or amble. 



4. Cursorial: Swift, light-limbed animals, 



which leap, gallop, and trot. 



Subplantigrade and spreading; feet short, 

 limbs sharph' angulate. 



Digitigrade or partly unguhgrade; feet 

 secondarilj' widened; digits of hind foot 

 often reduced in number (from an earlier 

 subcursorial phase), limbs more or less 

 angulate. 



Rectigrade; feet very short and wide; pha- 

 langes very short, terminal phalanges 

 usually reduced; limbs straight or post- 

 like. 



Unguligrade; feet very long, narrow, with 

 marked digital reduction; terminal pha- 

 langes large; limbs strongly angulate. 



Pantolambda, Hyrax, and 

 sectivores and carnivores. 



many in- 



Tapirs, titanotheres (Mesatirhinus, 

 Manteoceras), Oligocene rhinoceroses 

 (Caenopus) . 



Oligocene titanotheres (Brontothe- 

 rium), Amblypoda (Coryphodon,. 

 Uintatherium) , Proboscidea. 



Most horses, antelopes, deer, titano- 

 theres (Lambdotherium) . 



In comparing members of different races or the 

 successive evolutionary stages of a single race we can 



FEMDR, 



Sliorieiring 



■witJv 



increasinff speed 



27.1 % of total leTTfftJt 



Lengtherixng 

 ■witlv 

 increasing Weight 

 48. 6 % of total lengt7T, 



TIBIA. 



Length remainijig relatively constant 



31.7% 



PES 



Lengthening 

 ■with, 

 increasing speed 

 41.1Yo of total lenffth. 



34.3% 



Shortening 

 ■with 

 increasing ■weight 

 17.1% of total length 



A 



Figure 670.- 



Hind limbs of cursorial and graviportal types, showing adaptive changes 

 in the length of pro.ximal and distal segments 

 A, Increasing length from proximal to distal segments in a cursorial limb (Neohipparion); B, decreasing length 

 from proximal to distal segments in a graviportal limb (Mastodon) . 



find in the body no stationary or nonevolving bony 

 segment which will serve as a norm, or fixed stand- 

 ard of comparison: every bone 

 is in a state of change; no 

 segment is constant in length 

 or in proportion to any adjoin- 

 ing segment or to the body as 

 a whole. Nevertheless if we 

 arbitrarily assume that the 

 proximal segment of the hind 

 limb is of the same length (100) 

 in all the animals measured 

 we can then show the relative 

 lengths of the remaining seg- 

 ments of the limb in terms of 

 the length of the femur. 



Indices. — These are the pro- 

 portions of a single limb bone, 

 like the femur, or of a single- 

 arch element, like the scapula. 

 For our purposes the least 

 breadth of a bone may sim- 

 ply be divided by the great- 

 est articular length and the 

 result expressed as a percent- 

 age. 



Ratios. — These are obtained 

 between two elements of a limb, 

 as, for example, the length of 

 the tibia divided by the length 

 of the femur gives what may be 

 called the tibiofemoral ratio. 

 This ratio method assumes that 

 every femur or humerus respec- 

 tively, in being taken as a norm, 

 is reduced to the same abso- 

 lute length (100). Examples of 

 such ratios are the following: 



