Temporal range: Changhsingian–Carnian
|Fossil specimen of Protorosaurus speneri, Teyler's Museum|
Protorosauria is an extinct clade of archosauromorph neodiapsids from the latest Permian (Changhsingian stage) to the early Late Triassic (Carnian stage) of Asia, Europe, North America. It was named by the English anatomist and paleontologist Thomas Henry Huxley in 1871 as a order.
Many species seem to have been adapted for an arboreal lifestyle, including the "delta-winged glider" Sharovipteryx, while others, such as Tanystropheus, had extremely long, stiffened necks (possibly used to catch fish), and may have been at least partly aquatic. Other enigmatic reptile groups have sometimes been classified as belonging to the Protorosauria, including the drepanosaurids, Longisquama, and the pterosaurs.
Protorosauria was considered to be a synonym of Prolacertiformes for many years. However, most 21st century studies on the phylogeny of "prolacertiformes" indicate that the group as traditionally conceived is polyphyletic; while most prolacertiformes form a clade of basal archosauromorphs, Prolacerta itself is closely related to more derived archosauriforms.
Most phylogenetic analyses since 1998 have found a strongly supported clade that includes only the genus Prolacerta and the Archosauriformes. Protorosaurus and all other traditional prolacertiforms were recovered in more basal position, usually forming a single clade. Because the name Prolacertiformes is defined based on the genus Prolacerta, the name Protorosauria is used for the remaining group. Most of these analyses, such as Dilkes (1998), Sues (2003), Modesto & Sues (2004), Rieppel, Fraser & Nosotti (2003), Rieppel, Li & Fraser (2008), Gottmann-Quesada and Sander (2009) and Renesto et al. (2010), recovered large Protorosauria, that includes Protorosaurus, Drepanosauridae (and relatives) and Tanystropheidae (and relatives). However, some analysis found Protorosaurus (and sometimes the closely related Czatkowiella) to be more advanced or more basal than the node Drepanosauridae+Tanystropheidae, but always more basal than Prolacerta. The following cladogram shows the position of Protorosauria among the Sauria sensu Sean P. Modesto and Hans-Dieter Sues (2004).
While Senter (2004) re-assigned the bizarre, arboreal drepanosaurids and Longisquama to a group of more primitive diapsids called Avicephala, subsequent studies failed to find the same result, instead supporting the hypothesis that they were protorosaurs.
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