Wow That's a big Rock ! But Sorry I Can't see it as A Fossil
Perhaps Turtle shaped From that angle , But
I see Just a Large Rock.
At First Glance I Do see a Very Large Hand print
Then after a bit a Profile of a very Ugly Male Creature Facing Down.
But all Pareidolia {man-in-the-moon-syndrome} I'm sure
Don't Take that as Knowledge Just My opinion From my Personal Eyes
I added some photos not to the original post for some reason I'm confused on how to do that anyways take a look at the new photos and see if it does anything for you
Honestly don't know, and my guess I won't say, i was hoping someone would have an idea, its not dried mud or clay, is rock, very hard, acid had no reaction, found in northeastern Colorado
I see what you you're looking at. The hole is not an eye, it's a hole. The jaw shape is not a jaw. Look up some dinosaur fossil skulls. They don't resemble dinosaur recreations with flesh. Fossil bone is smooth, it has shape, it LOOKS like a bone, not a squint your eyes to see it thing, kinda sorta looks like a skull, it IS a skull. Keep looking.