What caused the dawn horse to go extinct?

Answer:the first known horses. They flourished in North America and Europe during the early part of the Eocene Epoch (56 million to 33.9 million years ago). Even though these animals are more commonly known as Eohippus, a name given by the American paleontologist Othniel Charles Marsh, they are properly placed in the genus Hyracotherium, the name given earlier by British paleontologist Richard Owen.

The "Dawn horses" were actually not related to horses! Recent studies of fossils found that "Dawn Horses" were buried in the same rock layers as modern horses! evolutionists were shocked at first but then decided that the "Dawn horse" was related to rabbits! Now to answer your question no one really knows why they went extinct. Evolutionist believe they changed into rabbits and Creationists (people who believe God created the universe and that evolution is incorrect) believe they died out due to climate changes after the global flood of Noah.