Phytosaur Skull Preparation

Back in November of 2008 I mentioned a new phytosaur skull collected from Petrified Forest National Park during the summer. Encased in a sandstone horizon of the Jim Camp Wash beds of the Sonsela Member (Chinle Formation), the skull is from the type locality of Pseudopalatus jablonskiae and was recovered about 100 meters from the spot where the type skull was collected. As I stated this skull is important because it may represent a second specimen of P. jablonskiae, but more complete than the type skull. Alternatively it could represent another phytosaur taxon which was a contemporary of P. jablonskiae. Because the skull is from the upper Jim Camp Wash beds, above the Jasper Forest bed it should be a pseudopalatine.

















The picture on the left shows the initial discovery. The skull is dorsal side up and beneath the rock hammer. Squamosals showing on the left [below the hammer handle] and the external nares showing on the right just below the hammer head. The picture on the right shows the beginning of the excavation. The sandstone was very well indurated and we needed a rock saw and hammers and chisels to block out the skull for removal. The resulting jacket weighed a few hundred pounds.

Late last week we cracked open the jacket and PEFO preparator Matt Brown started removing the rock. As of Tuesday morning this is what was exposed:

As you can see the upper left corner of the skull is now partially exposed. The squamosals are broad in dorsal view, thus the skull does belong to a pseudopalatine. The squamosals are more posteriorly extended than in the type of P. jablonskiae; however, this appears to be a larger specimen. Unfortunately the posterodorsal surfaces of the squamosals were what was exposed at discovery and thus were somewhat eroded. Also, the rock is much harder than we expected and the separation from the bone is not always clean. Some of the bone within the rock is actually fractured as it is softer than the surrounding matrix. Still, during excavation we located the tip of the premaxilla and both quadratojugals, so we are fairly certain that we have a complete and undistorted skull. Only time will tell. Over the next month or two I'm hoping to document the entire preparation process here and we will discover exactly what this skull is and how well it is preserved. Stay tuned.