Fifty million years ago an ancestor to modern horses, Hyracotherium, roamed much of North America. These ancestors to the modern horse were the size of a small dog and lived primarily in forests and scrub. As the climate became warmer and drier the forests were replaced with grasslands. The impact of this climate change on horse evolution can be seen in fossils of Merychippus, a longer legged ancestor of modern horses that roamed grasslands fifteen million years ago. Equus is the only surviving genus in the once diverse family of horses. Species of Equus lived from 5 million years ago until the present. Living species include horses, asses, and zebras.
Diagram an evolutionary tree that includes all five species mentioned in the passage above.
horses asses zebras