AdvertisementNew Evidence Suggests Humans Arrived In The Americas Far Earlier Than ThoughtApril 26, 2017Christopher JoycefacebookEmail(Left) A close-up view of a spirally fractured mastodon femur. (Right) A boulder discovered at the Cerutti Mastodon site in San Diego County thought to have been used by early humans as a hammerstone. (Tom Démeré/San Diego Natural History Museum)