From USA Today (hat tip Floyd):

Eric Stamatin and Andrew Gainariu
were doing what 11-year-old boys do — fishing, catching crayfish and
gathering sticks and rocks to build a dam at a stream near Eric’s home
last June.

But then the pair
stumbled upon something that most sixth-graders only dream of — they
discovered a 13,000- to 14,000-year-old American mastodon bone.

“I
thought it was a very weird rock,” Eric said this week from his Shelby
Township home in suburban Detroit near where they found the bone in a
stream.