A slightly new take on the new Poposaurus skull

More thoughts on the new Poposaurus skull (Fig. 1) that we looked at earlier (since modified). Slightly raising the broken maxilla ascending process puts a new spin on the possibilities for the skull shape and brings it into line with multi-documented sister taxa like Lotosaurus and Shuvosaurus.

Figure 4. The restored skull of the PEFO specimen referred to Poposaurus based on the Nesbitt identification of the anterior as a maxilla. The blue articular is not part of the PEFO specimen, but is described as a Poposaurus articular by Parker and Nesbitt (2013) scaled to fit. Their scale bars indicate it was 4x larger, which may be a typo. As is, the elements are part of a longer, more robust skull than any other poposaurid. See the revised skull reconstruction, figure 1B.

Figure 4. The restored skull of the PEFO specimen referred to Poposaurus based on the Nesbitt identification of the anterior as a maxilla. The blue articular is not part of the PEFO specimen, but is described as a Poposaurus articular by Parker and Nesbitt (2013) scaled to fit. Their scale bars indicate it was 4x larger, which may be a typo. As is, the elements are part of a longer, more robust skull than any other poposaurid. See the revised skull reconstruction, figure 1B.

The teeth
The teeth are indeed sharp. Parker and Nesbitt 2013 described them as belonging to a hyper-carnivore. But in the large reptile tree Poposaurus nests with beaked herbivores. In the fossil the teeth really don’t descend very much beyond the jawline. They are deeply rooted and triangular, not long and recurved.

Other indicators
Earlier we noted the less than trenchant claws on the forelimb, more appropriate for an herbivore than a carnivore. The cervicals are quite robust, able to handle a taller skull. The new reconstruction, with a possible raised maxilla ascending process, opens the possibility of a taller skull with a larger orbit, also more like an herbivore and more like its sisters.

Figure 1. Revised skull reconstruction for the PEFO specimen. Here the anterior is considered a premaxilla. Those teeth are shaped like triangles, but they are very deeply rooted and exposed very little, which casts doubts on its hypercarnivory.

Figure 1. Revised skull reconstruction for the PEFO specimen. Here the anterior is considered a premaxilla. Those teeth are shaped like triangles, but they are very deeply rooted and exposed very little, which casts doubts on its hypercarnivory.

At this point it’s just best to explore possibilities, some indicated by phylogenetic bracketing. That skull remains quite incomplete.

References
Gauthier JA, Nesbitt SJ, Schachner ER, Bever GS and Joyce WG 2011. The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Mehl MG 1915. Poposaurus gracilis, a new reptile from the Triassic of Wyoming. Journal of Geology 23:516–522.
Parker WG and Nesbitt 2013. Cranial remains of Poposaurus gracilis (Pseudosuchia: Poposauroidea) from the Upper Triassic, the distribution of the taxon, and its implications for poposauroid evolution. Geological Society, London, Special Publications 379: 22 pp.

wiki/Poposaurus

3 thoughts on “A slightly new take on the new Poposaurus skull

    • I’ve started taking a good look at this specimen. This is not Poposaurus. I found the specimen here: collections.peabody.yale.edu/search/Record/YPM-VP-057103. Nesbitt determined that it was cf. Dromicosuchus, but that seems dubious. Since it was published online twice at least, I will add it to the LRT.

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