The ancient bison (Bison antiquus) is an extinct bison species that lived in North America at least 60,000 years ago until about 10,000 years ago during the Late Pleistocene and Early Holocene. The species was first described in 1852 by Joseph Mellick Leidy, who named it Bison antiquus, which literally means “ancient wild ox” in Latin. The Ancient bison was about 15-25% larger than modern bison, reaching 7.4 feet tall and 15 feet long, with a maximum weight of 3,501 pounds and an average weight of about 1,800 pounds. Its horns averaged about 2.85 feet from tip to tip but could reach up to 3.5 feet. The first bison in North America were steppe bison (Bison priscus) that migrated from Siberia into Alaska via the Bering Land Bridge around 240,000 years ago. Over time, the steppe bison evolved into long-horned bison (Bison latifrons) which then evolved into ancient bison. Modern American bison (Bison bison) are believed to be either directly descended from ancient bison or the result of a hybridization between ancient bison and Bison occidentalis. Extinct bison are so abundant in the fossil record that they are considered indicator fossils, or fossils whose presence give an indication of geological time, specifically marking the Rancholabrean North American Land Mammal Age (240,000 to 11,000 years ago).