On this day in US history, scientists published what is believed to be the oldest known artwork in the Americas on June 12, 2011. An engraving was discovered on a fossil bone dated at least 13,000 years old, most likely from a mammoth, giant sloth, or even a mastodon. One thing: a fossil bone was engraved with an image of what appears to be an Ice Age-era mammoth. The discovery was made in Florida.