_Miohippus_ will also give rise to somewhat larger forest horses that will survive on into the Pliocene in patches of woodland. They will be little changed except in size (some came to be nearly as large as the modern horse), and some of them will even cross the Bering Land Bridge into Eurasia. This is the last time, however, that we’ll see these primitive horses in large numbers here in North America.
There’s another herd of small horses moving across the plain toward the river from the south. These are feeding as they move across the savanna, eating both leaves from the scattered trees and grass from the prairie. They seem to be enjoying their mixed diet and thriving on it, so they won’t be too badly hurt in the geologically near future when they have to eat mostly grass. This is _Parahippus_ (“near horse”), a new kind of horse just recently evolved from _Miohippus_.
_Parahippus_ is a horse of destiny. For a long time some individuals of _Miohippus_ carried a little extra wrinkle of enamel on the crowns of their upper grinding teeth—and now the wrinkle occurs in all individuals of _Parahippus_. Because of it, _Parahippus_ can eat grass without wearing out its teeth before reaching breeding age, making it possible for most individuals to reproduce before dying. The little wrinkle is passed on. It’s only a small advantage, but such is the stuff that survival and evolution are made of. _Parahippus_ is the forerunner of a vast array of different three-toed, long-limbed prairie horses that will be the most numerous members of their family until nearly the end of the Pliocene. From one of their descendants will come the first one-toed horse—the direct ancestor of our modern horses.
More herds are moving in on the river as the morning grows. There’s a group of something very small moving through the tall grass, but it’s completely hidden. Only the swaying of the 60-centimeter-tall blades shows that a number of animals are hurrying toward the river. Now they’ve moved out into an area of cropped grass, and we can see a herd of the diminutive deerlike _Nanotragulus_ (“dwarf goat”). Not a great deal larger than a house cat, these little “deer” have tall grinding teeth well adapted for grass-eating. Their ancestry goes back for millions of years into the Late Eocene, when some of their ancestors stood less than 15 centimeters (6 inches) high at the shoulder. But their entire family is soon to become extinct. They are part of the grazing community, although they eat leaves and softer vegetation just as readily. We call them “deer” because they look just like miniature deer, but the two families are really only distantly related.