Field of Science

Phytosaurs Everywhere

Easily the most common type of fossil in the Chinle Formation are the skulls of phytosaurs. Historically researchers from the University of California Museum of Paleontology, the United States National Museum, and the American Museum of Natural History came to the Petrified Forest to collect Triassic fossils for their collections and inevitably came away with several phytosaur skulls as the result of their labor.

Since I started at the park in 2001 my students and I have discovered and collected eleven complete and partial skulls, seven of them in the last two summers. Our most recent was discovered this last Tuesday and we were able to get it back to the lab by Wednesday afternoon.

The photo below shows the upper portion of the skull after being exposed. Half of the lower jaw is also present and slightly visible under the boulder to the left.

Below is a photo of the rear portion of the left side of the skull. The squamosal bone (the dark gray mass in the center of the photo) is narrow in dorsal (top) view and deep in lateral (side) view. Thus the skull is almost certainly that of a "Leptosuchus". Interestingly in 1921 Annie Alexander and Charles Camp of the University of California Museum of Paleontology collected the holotype skull of "Machaeroprosopus" ("Leptosuchus") lithodendrorum from a spot close by and at the same stratigraphic horizon.

The forward portion of the lower jaw was in a very hard sandstone matrix underneath a very large boulder at the site. In this third photo you can see the upper part of the skull already plastered and one of my interns is taking a turn under the boulder freeing the lower jaw. We were able to get it out and back to the preparation lab.


This hopefully will prove to be another nice skull for our collections.

5 comments:

  1. Hmm, I would say isolated phytosaur teeth and osteoderms are much more common than phytosaur skulls.

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  2. Yeah, you are probably correct. What I should have said is that phytosaurs are the most common fossils. However, if you consider isolated skull bone fragments and count the teeth as part of the skull thn my statement is correct. :)

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  3. I'm curious, Bill. Do you find that these skulls and skull fragments are often found isolated without any other postcrania or are there, indeed, other elements there or thereabouts, or does it simply depend where you are in the Chinle?

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  4. That last photo should be captioned "Palaeontologist applies for a Darwin award".

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  5. Saurian,

    We mainly find isolated skulls and skull elements. Unfortunately often the skulls are separated from the rest of the carcass and often disarticulate themselves. Thus to find the upper part of the skull and one half of the mandible is a good find.

    Mike,

    The photo looks scarier than the situation really was. Good call though.

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