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According to what I looked up Palo Duro has lots of marine fossils. I first found a photo of an ammonite with deep ridges but not as deep. There was also a picture of a pecten shell showing these ridges. Although I could find no mention of the species your specimen closest matched Helicoprion which is a strange shark species. Cant confirm this as there is no scale. Its worth your while to have it looked like by someone from a museum?

Thank you so much @lynette-luff!