Update: I found a mandible in the travertine floor at my parents house

This is presumably a 1 million year old homo erectus jaw, since it's from the same quarry as -

https://en.wikipedia.org/wiki/Kocaba%C5%9F_cranium

Interesting true story.

It reminds me of this interesting false story, that should never be lost under layers of internet geologic sediment.

https://www.snopes.com/fact-check/smithsonian-barbie/