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.
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.
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