Wow!, the upper or lower mandible of a (prehistoric dinosaur?) Well, maybe not a prehistoric dinosaur, maybe a prehistoric reptile, or bird, but I'd say it's pretty obvious that it's a petrified mandible of a creature I'm certainly not familiar with. What's so peculiar to me, is how different teeth on one side of the jawbone compared to the other.
I would be stoked to find something like that! I assume you found it USA1, If so how about some information