OK...this really is a mystery fossil because I am not really sure what it is. It was collected in 2002 from Petrified Forest National Park in the Blue Mesa Member of the Chinle Formation. It was found in a bluish mudstone layer that contains lots of in-situ tree stumps but hardly any vertebrate fossils. This layer occurs just below an extremely productive horizon which produces a wealth of typical Chinle vertebrates (phytosaurs, aetosaurs, metoposaurs, etc...).
I'm sorry for the slightly blurry photo and only one angle but that is all I have right now. I first thought that it was a scapula, but I guess that it could also be a paroccipital process of the opisthotic and a portion of the exocipital of a pseudosuchian archosaur. The scale bar = 5 cm.
I'm open to either other suggestions and/or votes on my hypotheses.
in The Biology Files