Protylopus is an extinct genus of a primitive horse-like mammal that lived about 50 million years ago. It is also known as a "dawn horse" because it is believed to be the earliest known ancestor of modern horses. Synonyms for "protylopus" include "Paratoceras," "Plioceras," and "Ariacetus." These synonyms are often used by scientists when referring to specific species of the genus or when describing evolutionary relationships between different members of the equine family tree. Despite its relatively simple anatomy, the protylopus played a significant role in the evolution of the horse, and its study has greatly aided researchers in understanding the history of this important mammalian group.