Parahippus

From Freepedia

Parahippus is an extinct ancestor of the modern horse, very similar to Miohippus, but was slightly larger.

About twenty million years ago, during the Miocene Period, the earth was drastically changing. Great plain were developing, forests were thinning out, mountains were forming, and swamps dried up. This brought about many changes in the existing horse ancestors. Since leafy food had become scarce, it had to eat the grass of the plains. The molar teeth developed high crowns and a hard covering for grinding the grass, which was usually covered with dust and sand. Also, body size increased and the legs and face lengthened. The bones in the legs fused. This, along with muscle development, allowed the parahippus to move with forward-and-back strides, causing flexible leg rotation to be eliminated. Most importantly, parahippus was able to stand on its middle toe, which gave them the ability to run faster, instead of walking on pads; their weight was supported by ligaments under the fetlock to the big central toe. Their side toes seldom touched the ground.

The extra crest that was variable in Miohippus became permanent in Parahippus. Also, other teeth were beginning to form a series of tall crests with higher crowns. Later fossils of this horse are so similar to Merychippus that it is difficult to distinguish the two.