Today’s blog will tag on the heels of “Nomenclature revisions (part 1) to highlight a number of putative clades that are in need of revision, are no longer valid or are redundant in light of the new reptile tree (which is larger than any prior attempt and encompasses all the major clades).
Laurin (1991) defined the Diapsida as the most recent common ancestor of araeoscelidians, lepidosaurs and archosaurs and all its descendants. Here that definition is redundant with Reptilia because lizards are not related to archosaurs except through Cephalerpeton, the basalmost reptile.
Benton (1990) referred the term Diapsida to the clade stemming from the first amniote with a supratemporal fenestra homologous with that of Aves. That definition may be retained despite the revelation that the diapsid opening of Sphenodon was not homologous with that of Aves because lepidosauriformes were not related to the basal diapsid, Petrolacosaurus. A node-based redefinition of the new Diapsida is proposed to include Petrolacosaurus, Triceratops, their last common ancestor and all of its descendants. It is equivalent to the definition of Benton (1990).
Taxa traditionally considered “younginiformes,” such as Youngina, Acerosodontosaurus \ and Thadeosaurus do not form a monophyletic group. Here they form a basal assemblage of a larger clade. The Younginimorpha is proposed to include Thadeosaurus, Triceratops, their last common ancestor and all of its descendants.
Prolacertiformes / Protorosauria
Protorosauria no longer include tanystropheids, pterosaurs and kin. Those have all been shifted to the Squamata. The clade Protorosauria has been reduced to only Prolacerta, Protorosaurus, Pamelaria, Boreopricea and kin, all basal taxa to the Archosaurifomes. Redefined, the new Protorosauria is proposed to include Prolacerta, Protorosaurus, their last common ancestor and all of its descendants. A more inclusive clade, the new Prolacertiformes, is proposed to include both Protorosauria + Archosauriformes. Redefined as a node-based taxon, the new Prolacertiformes is proposed to include Prolacerta, Triceratops, their last common ancestor and all of its descendants. Orovenator is the outgroup taxon.
Gauthier (1986) proposed the term “Archosauriformes” to replace the traditional Archosauria (Proterosuchus through Dinosauria). Gauthier’s Archosauriformes retained the Proterosuchidae, Parasuchidae, Proterochampsidae, Euparkeria, Erythrosuchidae, and the Pterosauria, all taxa conventionally thought to lead to and include the Dinosauria. This needs to be revised. Here pterosaurs now nest with lizards, but the other listed clades are retained. Other former outgroups are now added. These include the Choristodera and Youngina. Not all taxa had an antorbital fenestra (see below). Redefined here, the new Archosauriformes is proposed to include Champsosaurus, Triceratops, their last common ancestor and all of its descendants. A specimen of Youngina (UC 1528) nests at the base.
The Basal Division Within the Archosauriformes
The new Archosauriformes divides at its base into two major clades, the Pararchosauriformes and Euarchosauriformes. This division was previously unnoticed in prior studies due to exclusion of several basal taxa including several specimens of Youngina.
The Pararchosauriformes includes Chañaresuchus, Champsosaurus, their last common ancestor and all of its descendants. This now extinct clade also includes choristoderes, parasuchians, Doswellia, Cerritosaurus and Lagerpeton, among others.
The Euarchosauriformes includes Proterosuchus, Triceratops, their last common ancestor and all of its descendants. This clade also includes crocodilians and birds among others. It does not include proterochampsids, parasuchians, choristoderes and kin.
More to come in part 3.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
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Dilkes D 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Phil Trans R Soc B 353: 501–541.
Gauthier JA 1986. Saurischian monophyly and the origin of birds, In Padian K editor. The Origin of Birds and the Evolution of Flight, 1–55. Memoirs Calif Acad Sc 8.
Gauthier J, Kluge AG and Rowe T 1988. Amniote phylogeny and the importance of fossils. Cladistics 4: 105–209.
Gauthier J, Estes R and de Queiroz K 1988. A phylogenetic analysis of Lepidosauromorpha, In Estes R, Pregill G, editors. Phylogenetic relationships of the lizard families, 15–98. Stanford: Stanford U Press.
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Laurin M 1991.The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny. Zoological Journal of the Linnean Society 101: 59–95.
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