Paliguana whitei (Broom 1903) Earliest Triassic ~250 mya, ~ 2 cm in skull length, has always been recognized as a basal lepidosauriform. It is the first in its lineage to have an upper temporal fenestra, but note that the lower temporal bar, last seen in Lanthanosuchus and Macroleter, has been missing for several intervening taxa. Thus the skull of Paliguana can only be considered quasi-diapsid. Among the lepidosauromorph only derived taxa like pterosaurs and Sphenodon have true diapsid-style skulls due to the reappearance of the quadratajugal bar. In any case, none of these taxa are closely related to Petrolacosaurus and Youngina, as previously reported using smaller datasets. Here Paliguana is derived from a sister to Owenetta and Candelaria. Paliguana phylogenetically precedes Saurosternon and Homoeosaurus.
Smaller and distinct from Candelaria, the skull of Paliguana had a straight rostral profile and an upwardly curving rostrum. The jugal produced a short quadratojugal process, despite the virtual absence of the quadratojugal (perhaps a remnant on the quadrate). The prefrontals were broader, as in Owenetta. The lateral temporal fenestrae merged with the reduction of the squamosal and its disconnect from the jugal. An upper temporal fenestra was created posterior to the postfrontal and postorbital formed primarily from the embayment of the parietal and secondarily to the reduction of the supratemporal (here combined with the squamosal in yellow). Crushing and cracking in the specimen makes identification difficult. There is no supratemporal overhang at the back of the skull.
Paliguana and Saurosternon nest at the base of the Lepidosauriformes, defined by Gauthier, deQuieroz and Estes (1988) as Sphenodon and squamates and all organisms sharing a more recent common ancestor than they do with younginiforms. They intended this to include Paliguana, Saurosternon, Kuehneosauridae, Rhynchocephalia and Squamates, but in the context of the present study their Lepidosauriformes would be redundant with the current Lepidosauromorpha. Redefined, the Lepidosauriformes now includes Paliguana, Sphenodon, their most recent common ancestor and all of its descendants.
That now includes rhynchosaurs, trilophosaurs and pterosaurs which were formerly excluded.
See the complete tree. |
