MECHANICS OF LOCOMOTION 

 Measurements, in millimeters, and ratios oj limbs of mediportal ungulates 



737 



Tibio- 

 femoral 

 ratio 



Meta- 

 tarso- 



femoral 

 ratio 



Radio- 

 humeral Mtc III 

 ratio 



Meta- 



carpo- 



humeral 



ratio 



Amynodontidae: Amynodon intermedius 



Tapiridae: 



Tapirus terrestris 



Tapirus indicus 



Titanotheriidae : 



Palaeosyops major 



Palaeosyops leidy i 



Manteoceras manteoceras 



Mesatirhinus petersoni 



Limnohyops monoconus 



262 

 320 



433 



370 



390? 



358 



387 



'300 



208 



258 



332 

 290 

 272 

 283 

 283 



71 



79 

 80 



77 

 78 



108 

 120 



137 

 110 



205 

 250 



177 

 228 



91 



106 

 120 



325 



235 



113? 

 107 



118 

 123 



293 



228 



50 



4S 



34?- 



Phyletic -progression to cursorial type in the Eguidae. — 

 The above "primitive cursorials" constitute the type 

 from which the "modern cursorials" evolved. The 

 Equidae in their progression into the "modern cur- 

 sorial" type present exactly the reverse of the gravi- 

 portal progression seen above in the Amblypoda. 

 They show a relative elongation of the tibia, radius, 

 metatarsus, and metacarpus. After attaining the 



highest speed ratios in the lower Pliocene Hipparion 

 (Neohipparion) wMtneyi we observe a retrogression, 

 toward the more heavy-bodied modern Equus type 

 and a still greater retrogression into the short-limbed 

 and slow-moving Hippidion neogaeum of South 

 America and in the still shorter-limbed Hyper- 

 Jiippidium. This is one of the most significant series 

 of comparative ratios which we have obtained. 



Measurements, in millimeters, and ratios showing cursorial progression 



Meta- 

 carpo- 



Primitive : Eohippus 



Intermediate: 



Mesohippus bairdii 



Mesohippus sp 



Hypohippus osborni 



Neohipparion whitneyi 



Equus kiang 



Equus caballus " Elmer Weeks" 



Equus scotti 



Retrogressive: Hippidion neogaeum. 



53 



69? 



68 



99 

 116 

 100 



78 



84 



72 



Cursorial light-bodied artiodactyls. — These animals 

 are convergent with or analogous to the Equidae, 

 yet in the elongation of the tibia they surpass even 



the Hipparion {Neohipparion) ratios and attain in 

 Gazella and Antilocapra the highest speed ratios 

 known. The list is as follows: 



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



Primitive : 



Eotylopus reedi 



Tragulus napu 



Forest-living: Odocoileus hemionus. 



Plains-living: 



Antilope cervicapra 



Antilocapra americana 



Gazella dorcas 



