About 40 million years ago, the evolutionary process began to change the horse even more. At this time, during the Oligocene Epoch, appeared Mesohippus. As the temperature and climate changed, forests began to dwindle and grass became more prevalent. Mesohippus developed larger than its ancestors, standing 24 inches high at the shoulders, about the size of a collie dog. The 44 teeth remained, however, and legs and face began to lengthen.
Its feet were still clinging to pads but tiny hooves had developed on three toes on the front and three toes on the back feet. It was better suited to running fast to escape the enemies that pursued. Because the swamp had given way to soft ground, Mesohippus no longer needed its toes so much as Eohippus did.
The lateral supporting toes gradually decreased in size while the middle toe gained strength. Some of these horses migrated across the Bering Strait to preserve the species, which were eventually wiped out on the North American continent for unknown reasons.
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