For over 150 years, paleontologists, the “bone hunters”, have been studying the fossils of horses. Humans probably were finding them long before, seeing them as strange creatures in the stone and sand. Even though horses originated in North America, horses disappeared from North America during the period of time known as the “Ice Age”. Researchers believe that horses migrated into Siberia across a land bridge that once connected Alaska to Siberia. This land bridge is now under the ocean but is called the Bering Strait today. Horses then spread out into Siberia into Asia and in many parts of Europe. Meanwhile, back in North America, all remaining horses died out. What happened to them? There may have been several reasons that, added together, caused the extinction of horses in North America. There was a dramatic change in the climate, there could have been disease or parasites that weakened the horse populations, competition for food sources may have left less for horses. Predators, including humans who hunted horses for food, may have contributed to their extinction. Other species survived the Ice Age, but animals like camels, mastodons, rhinoceros and sabre-toothed tigers did not, so it could be simply a failure to adapt to the environment.