Florida Museum of Natural History

The central digit of horses became increasingly stronger while the "side toes" became less important and are virtually lost in the modern horse.

Follow this by examining the reduction and loss of metacarpal V (red) and its digits (fingers). Do this likewise for metacarpals II (orange) and IV (green). Note that no horse ever had a thumb (I).

Reduction and loss of side toes minimizes the weight at the extreme end of the foot. This reduces the torque, so the horse's limb may move faster.

Hyracotherium toe bones Miohippus toe bones Merychippus toe bones Equus toe bones Built for speed!
Hyracotherium
55 - 45 mya
Miohippus
33 - 29 mya
Merychippus
17 - 11 mya
Equus
mya
 
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