The bone is believed to have belonged to a member of the Hohokam people, an ancient group considered to be ancestors to modern Native Americans in Arizona.
Archaeological experts say the discovery is a cautionary tale about the consequences of citizen investigators taking matters into their own hands.
Until now, estimating how old a dinosaur was when it died has been a fairly simple process: Count up the growth rings in the fossilized bones. But new research into some of dinosaurs' living relatives, like crocodiles, suggests that this method may not always work.