A Virtual Phytosaur Endocast and its Implications for Sensory System Evolution in Archosaurs
Many recent studies have detailed the morphology of archosaurian endocrania. However, the outgroup to Archosauria, Phytosauria, has yet to be studied with modern techniques that would allow reconstruction of their internal anatomy. Pseudopalatus mccauleyi is a derived phytosaur from the Upper Triassic Chinle Formation, Arizona. A skull of P. mccauleyi, USNM 15839, was imaged using computed tomography in order to create the first high-quality, digitally reconstructed phytosaur endocast. Pseudopalatus mccauleyi exhibits overall endocast morphology that is similar to that of an extant crocodylian. These clades, phytosaurs and extant crocodylians, exhibit convergent Baupläne and similar inferred ecologies. A notable difference between the endocasts of the two clades is a considerable dural expansion in P. mccauleyi that denotes a large pineal body. This expansion, and the overall morphology of the endocast, is consistent with the historic endocranial reconstructions of the phytosaurs Pseudopalatus buceros, Smilosuchus gregorii, and Parasuchus hislopi. A comparison with phylogenetically diverse archosaurian endocasts reveals that endocast morphologies are highly conserved within Pseudosuchia, regardless of Bauplan or ecology. This conservatism is in contrast to the diversity of endocast morphology observed within Theropoda and Sauropodomorpha, or between members of those clades and Pseudosuchia. The most pronounced variability in pseudosuchian endocast morphology is a trend in size reduction of the pineal region, from a large basal condition to a reduced derived condition wherein the pineal region is indistinguishable from the rest of the endocast. A similar trend in pineal reduction is also seen in theropods and sauropods.
Journal of Vertebrate Paleontology
Holloway, Waymon L.; Claeson, Kerin M.; and O'Keefe, F. Robin, "A Virtual Phytosaur Endocast and its Implications for Sensory System Evolution in Archosaurs" (2013). PCOM Scholarly Papers. 171.