Prolacertiformes? Protorosaurs? Or Zumzeen Else?

Figure 1. Click to enlarge. The list of prolacertiforms according to Wikipedia. Here only the taxa in black on white actually nest with Prolacerta. The others (red on yellow) are Tritosaurs, members of the new third squamate clade.

Separating the Old Prolaceriformes
From the New Tritosaurs
There has been some confusion regarding the Prolacertiformes (aka Protorosauria according to Rieppel et al. 2993). Wikipedia reports that all the taxa in Figure 1 were prolacertiforms. The large reptile study found otherwise. Only those in black on white were supported as true protorosaurs. Some, like Kadimakara, are based on scraps (that I have not seen or read about yet, so they get the benefit of the doubt). The other taxa, red on yellow, are not prolacertiformes, but tritosaurs, members of the new third clade of squamates that also included pterosaurs and drepanosaurs. The lack of awareness of the Tritosauria may be the source of the phylogenetic confusion. An overarching cladistic analysis, shown here, may be the only way to identify and separate the new tritosaurs from the old protorosaurs (which most workers and Wiki still refer to as prolacertiforms).

Distinct from Tritosaurs
The confusion arises due to the large amount of convergence in the two clades. First and foremost, there is the long neck, but each vertebra is deeper than wide in protorosaurs, not so in tritosaurs. Only the tritosaurs had an ossified sternum, a displaced naris and an elongated pedal 5.1. The phalangeal patterns were also distinct. Only prolacertiforms had deep chevrons (although drepanosaurs redeveloped their own versions by convergence).

Distinct from Its Sisters Among the Younginiforms
No known protorosaur had a complete lower temporal arch. The lateral rostral shape was straight. The mandible tip descended. The ventral pelvis was fused. The tibia was as long as the femur. The proximal tail was much deeper than the whip-like distal end, which had no chevrons. All these traits find convergence elsewhere on the tree. Otherwise, protorosaurs initiated a suite of traits found in more derived archosauriforms or terminated traits found in more basal reptiles.

So What’s Left on the Prolacertiform List?
Despite the deletions, that still gives us a wonderful variety in size and morphology within the clade of Prolacerta sisters, including Protorosaurus, Pamelaria, and Boreopricea (Fig. 2). Czatkowiella is not shown, but it was also tiny. Malerisaurus langstoni (from North America) was recently considered a chimaera based on at least four taxa (Spielmann et al. 2006). The Malerisaurus robinsonae, from India, remains a valid genus. The outgroup taxon for this clade, Orovenator, was tiny by comparison. The BPI 3859 specimen of Youngina, a sister outside the protorosaurs at the base of the Archosauriformes, was also relatively tiny. Orovenator Likely preceded Youngina without intervening taxa. That clade kept producing descendants long after the last of the protorosaurs died out in the Triassic.

The Protorosaurs, Malerisaurus, Prolacerta, Protorosaurus, Pamerlaria and Boreopricea.

Figure 2. Click to enlarge. The Protorosaurs, Malerisaurus, Prolacerta, Protorosaurus, Pamerlaria and Boreopricea.

Chatterjee considered Malerisaurus bipedal, arboreal and aquatic. Similar claims have been advanced for the morpholotically similar tritosaur, Macrocnemus. Protorosaurs appear to have been terrestrial insectivores to carnivores, perhaps similar to modern varanids in their diet, locomotion and habits.

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.

Benton MJ and Allen JL 1997. Boreopricea from the Lower Triassic of Russia, and the relatioships of the prolacertiform reptiles. Palaeontology 40 (4):931-953.
Borsuk−Biaynicka M and Evans S E 2009. A long−necked archosauromorph from the Early Triassic of Poland. Paleontologica Polonica 65: 203–234.
Chatterjee S 1980. Malerisaurus. A new eosuchian reptile form the Late Triassic of India. Royal Society of London Philosophical Transactions (B) 291:163-200.
Evans SE and King MS 1993. A new specimen of Protorosaurus  (Reptilia: Diapsida) from the Marl Slate (Late Permian) of Britain. Proceedings of the Yorkshire Geological Society 49, 229–234.
Gottmann−Quesada A and Sander PM 2009. A redescription of the early archosauromorph Protorosaurus speneri Meyer, 1832 and its phylogenetic relationships. Palaeontographica A 287, 123–220.
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Modesto SP and Sues H-D 2002. The skull of the Early Triassic archosauromorph reptileProlacerta broomi and its phylogenetic significance. Zoological Journal of the Linnean Society, 140:335-351.
Parrington FR 1935. On Prolacerta broomi gen. et sp. nov. and the origin of lizards. Annals and Magazine of Natural History 16, 197–205.
Rieppel OC, Fraser NC, Nosotti S 2003. The monophyly of Protorosauria (Reptilia, Archosauromorpha): a preliminary analysis. 1 Atti della Società Italiana di Scienzi Naturale 144(2):359-382
Seeley K 1888.
 Research on the structure, organisation and classification of the fossil Reptilia 1. On the Protorosaurus speneri (von Meyer). Philosophical Transactions of the Royal Society, London B 178, 187–213.
Sen K 2003. Pamelaria dolichotrachela, a new prolacertid reptile from the Middle Triassic of India. Journal of Asian Earth Sciences 21: 663–681.
Spielmann JA, Lucas SG, Hunt AP and Heckert AB 2006. Reinterpretation of the holotype of Malerisaurus langstoni, a diapsid reptile from the Upper Triassic Chinle Group of West Texas. New Mexico Museum of Natural History and Science Bulletin, v. 37, p. 543-547.
Tatarinov LP 1978. Triassic prolacertilians of the USSR. Paleontological Journal 12(4):505-514



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