Pseudopalatus

Pseudopalatus. Image modified from original by Jeff Martz.

Meaning: "false palate"

Species: P. pristinus Mehl, 1928; P. buceros Cope, 1881; P. mccauleyi Ballew, 1989; and P. jablonski Parker and Irmis, 2006

Nominal Author: Mehl, 1928

Age: Late Triassic

Location: Southwestern USA

Physical Characteristics: A large (3-4 meter) phytosaur with a robust rostrum and distinct dorsal crest.

Phylogenetic Position and Species Status

Currently, there are four species of Pseudopalatus, with P. pristinus and P. buceros being the most closely related and most derived and P. jablonskiae being the most basal (Parker and Irmis, 2006). It has been suggested multiple times that P. pristinus and P. buceros are sexual dimorphs of a single species (Camp, 1930; Colbert, 1947; Lawler, 1979; Zeigler et al, 2002; Zeigler et al, 2003), but the evidence is still inconclusive. The validity of P. mccauleyi as a species has also been contested (Long and Murry, 1995; Zeigler et al, 2002; Zeigler et al, 2003), but recent phylogenetic analyses have supported its position, especially when the newest species, P. jablonskiae, is considered (Ballew, 1989; Hungerbuhler, 2002; Parker and Irmis, 2006). The genus Pseudopalatus has been found to be most closely related to Redondasaurus, followed by Mystriosuchus, and when these three are combined with Nicosaurus, they constitute Pseudopalatinae (Hungerbuhler, 2002; Parker and Irmis, 2006).

Phylogeny of Pseudopalatinae from Hungerbuhler, 2002 (47 characters; tree length: 113; CI: 0.73; RI: 0.54; bootstrap values shown). A similar MPT was recovered by Parker and Irmis, 2006, with the addition of the newer species, P. jablonskiae (which was found to be the most basal member of Pseudopalatus).

A Revised Diagnosis of Pseudopalatus

With the addition of P. jablonskiae, Parker and Irmis revised the diagnosis of the genus in 2006. They included four of Hungerbuhler's characters, which include a strongly developed medial lamella of the postorbito-squamosal bar with the supratemporal fenestra reduced to a slit (character 19), a rounded top of the parieto-supraoccipital complex (character 24), the lamina of the squamosal extends onto the paroccipital process forming the ventrolateral border of the posttemporal fenestra (character 38), and a posttemporal fenestra less than three times wider than high (character 41) (2002). Pseudopalatus also differs from all other phytosaurs in that the dorsal position of the squamosals are mediolaterally expanded forming a shelf level with the parietal and postorbital (Parker and Irmis, 2006). Finally, Pseudopalatus differs from Redondasaurus in having a supratemporal fenestra that is visible in dorsal view.

Biostratigraphy

Pseudopalatus is a stratigraphically significant taxon. Lucas and Hunt (1993) designated Pseudopalatus as an index taxon for the Revueltian (early-middle Norian), with the first appearance datum for Pseudopalatus representing the end of the Adamanian land vertebrate faunachron and the beginning of the Revueltian land vertebrate faunachron. The addition of P. jablonkiae is significant in that it is the stratigraphically lowest occurrence of Pseudopalatus, suggesting an overlap of the Adamanian and Revueltian LVFs (Parker and Irmis, 2006).