Fossil? Found in Eastern, Montana

Found a fossil? Submit a post here containing a few images, and we'll figure out what it is!

Any thoughts? Durango CO, late April 2022

This subreddit helps users identify animal species from pictures, videos, audio or calls, tracks, dens, scat, etc. All ID requests should include the animal's LOCATION (country, state, city, name of ocean or coast). This sub is NOT for identifying breed info for cats/dogs or identifying insects/parasites. Comments should be helpful or educational only, and advice should be legal and humane. Welcome!