eohippus

/ˌiːoʊˈhɪpəs/
noun
  1. A small, extinct ancestor of the modern horse that lived about 50 million years ago.
    • The eohippus was only about the size of a small dog.
    • Scientists study eohippus to understand how horses evolved over time.
    • Fossils of eohippus have been found in North America and Europe.