Hello,
I recently found an extremely suggestive rock that mirrors a skull with a round object fused to it's jaw. I took it to a geologist from University of Georgia, Dr. Garrison. He estimated that it was approximately 250 million years old. He also said that it was a cast of a creature that died in sediment. The sediment filled in the organic parts and created a cast.
Definition of cast fossils: http://www.ucmp.berkeley.edu/paleo/fossilsarchive/casmol.html
I will attach some photos.
Also, Here is the direct link to a YouTube video of it:
https://youtu.be/01M7u7E84Dw
I really appreciate your time.