Nomenclature revisions (part 3)

Today’s blog will tag on the heels of “Nomenclature revisions (part 1 and part 2) to highlight a number of putative clades that are in need of revision, are no longer valid or are redundant in light of the new reptile tree (which is larger than any prior attempt and encompasses all the major clades). Today we’ll restrict our scope to the Archosauriformes.

The Euarchosauriformes

Figure 1. The Euarchosauriformes. Click to see more.

Erythrosuchiformes – new clade
A new definition for a monophyletic clade Erythrosuchiformes is proposed to include Erythrosuchus, Triceratops, their last common ancestor and all of its descendants. Vjushkovia had been traditionally considered an erythrosuchid but here it nests outside the Erythrosuchidae.

The Rauisuchia – retained
Rauisuchia was erected by Bonaparte to represent the clade including Rauisuchidae, Prestosuchidae, Poposauridae and Chatterjeeidae. Because Chatterjeea and Poposaurus now nest as dinosaurs, this definition of the Rauisuchia now includes all dinosaurs. Redefined as a more inclusive monophyletic node-based clade, the new Rauisuchia is proposed to include Vjushkovia, Triceratops, their last common ancestor and all of its descendants. Members also include crown-clade Archosauria and Ticinosuchidae (including Stagonolepidae). The more restricted Rauisuchidae now includes Vjushkovia, Smok, the last common ancestor and all its descendants.

Ticinosuchidae – new clade
and Ticinosuchus are basal to a clade that includes Qianosuchus and the Stagonolepidae. Within the new Rauisuchia, a definition for a monophyletic Ticinosuchia is proposed to include Ticinosuchus, Triceratops their last common ancestor and all of its descendants. The more restricted Ticinosuchidae is proposed to include Ticinosuchus, Qianosuchus, their last common ancestor and all its descendants.

Archosauria – retained
Still crocs, birds, their last common ancestor and all its descendants. No change here (except no pterosaurs, of course).

Suchia – paraphyletic
Krebs (1974) defined “Suchia,” as “Crocodylotarsi,” but not Parasuchia. Even so, such a clade remains paraphyletic here. “Suchia” had been described by Benton and Clark (1988) as Crocodylomorpha + “rauisuchians” + Stagonolepididae, but not Gracilisuchus =. Here, that assemblage also constitutes a paraphyletic group.

Pseudosuchia – redundant
In the pre-cladistic era, “Pseudosuchia” generally included Stagonolepidae, the old Rauisuchia, Ornithosuchidae and some basal crocodylomorphs. Here these form a a paraphyletic clade.

Gauthier and Padian (1989) defined “Pseudosuchia” as “crocodiles and all archosaurs closer to crocodiles than to birds. Gauthier 1986 and Senter (2004) created equivalent definitions. Unfortunately, here the “Pseudosuchia,” as defined by these authors, is redundant with the Crocodylomorpha.

Crocodylomorpha – retained, redefined
Parrish (1993) cited six synapomorphies from Walker (1964) when he embedded the old Crocodylomorpha within Rauisuchia.

Benton (1990) defined Crocodylomorpha as all archosaurs closer to Eusuchia than to Ornithosuchus or Postosuchus. While it is clear that Benton meant to include a clade similar to the present one, his definition with the present tree topology would include Ticinosuchidae (including Stagonolepidae), which was not his intention.

Sereno (2005) defined Crocodylomorpha as the most inclusive clade containing Crocodylus but not Poposaurus, Gracilisuchus, Prestosuchus and Aetosaurus. The omission of Gracilisuchus excludes a basal taxon in the present Crocodylomorpha.

A new node-based definition for the new Crocodylomorpha is proposed to include Crocodylus, Pseudhesperosuchus, their last common ancestor and all of its descendants. Ticinosuchidae is the outgroup. Scleromochlus, a taxon often nested with dinosaurs and pterosaurs [17–20,23] nests here (Figures 2) within the crocodylomorpha close to Gracilisuchus.

Crocodylotarsi – redundant
Benton and Clark (1988) defined “Crocodylotarsi” as the last common ancestor of crocodiles and Parasuchia. This represented the “crocodilian line” (Parasuchia, Rauisuchidae, Stagonolopedidae, Poposauridae and Crocodylomorpha) as opposed to the “bird line” (Ornithosuchia) as defined by Parrish (1993). In the present study that definition of Crocodylotarsi is redundant with Archosauriformes and furthermore the taxon list is paraphyletic.

Crurotarsi  – redundant
Sereno (1991) defined “Crurotarsi,” as all forms closer to Crocodylus than to Passer [146]. It was meant to include rauisuchians, phytosaurs (parasuchians), stagonolepids, poposaurs, sphenosuchians, and a few other groups including Ornithosuchidae. Here the definition is redundant with Crocodylomorpha. The taxon membership list is paraphyletic and redundant with Archosauriformes.

More coming in part 4. 

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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Benton MJ, Clark JC 1988. Archosaur phylogeny and the relationships of the Crocodylia. In Benton MJ editor. The phylogeny and classification of the tetrapods, 295–338. Syst Assoc, Sp Vol 35A, Clarendon:Oxford.
Bonaparte JF 1982. Classification of the Thecodontia. Geóbios, Mém Sp 6: 99–112.
Clark JM and Hernandez RR 1994. A new burrowing diapsid from the Jurassic La Boca formation of Tamaulipas, Mexico, J Vert Paleo 14: 180–195.
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Gauthier JA 1994. The diversification of the amniotes. In: Prothero DR, Schoch RM editors. Major Features of Vertebrate Evolution: 129-159. Knoxville: Paleo Society.
Gauthier JA, Padian K 1989. The origin of birds and the evolution of flight, In Padian K, Chure DJ editors. The Age of Dinosaurs: Short Courses in Paleontology, No. 2. 121–133. Paleo Soc Depart Geo Sci, Knoxville: U Tenn.
Krebs B 1974. Die Archosaurier. Naturwissenschaften 61: 17–24.
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.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
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Senter P 2004.Phylogeny of Drepanosauridae (Reptilia: Diapsida). J Syst Palaeo 2: 257–268.
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