Coelurosauravus (Fig. 1, Piveteau 1926, Late Permian ~250 mya, ~40 cm in length) was an arboreal lepidosauriform with an odd collection of dermal rods that opened laterally to produce ‘wings’ suitable for display or perhaps gliding. No one previously has produced an ancestor taxon.
including Mechistotrachelos, Icarosaurus, Kuehneosaurus and Xianglong, produced variations on the Coelurosauravus design, all convergent with the living rib-glider, Draco, an iguanid not related to any of the above taxa.
Coelurosauravus also has wide, temporal crests shared only with Mecistotrachelos. Earlier we discussed the homology of the dermal rods (not ribs) of kuehneosaurs with those of Coelurosauravus.
The outgroup taxon
in the large reptile tree for these odd arborealists is Palaegama (Fig. 1, Carroll 1975). It preserves no hint of lateral dermal rods and has no temporal crest. It is such an unpopular taxon that it has not yet earned a Wikipedia entry. Among 588 taxa in the large reptile tree, no other is closer to Coelurosauravus and the kuehneosaurs.
As a basal lepidosauriform,
Palaegama (Late Permian) also nests with the basalmost lepidosaurs, including the basalmost sphenodontid, Megachirella, the basalmost tritosaur Tijubina (Early Cretaceous) and the basalmost pre-squamate, Lacertulus (Late Permian), all ‘lizardy’ taxa of similar morphology.
Palaegama is really an important taxon nesting near the bases of several clades. It deserves more press, scrutiny and credit.
Distinct from predecessor taxa,
Palaegama has long strong limbs and long digits, like those of its headless sister, Saurosternon. The Palaegama skull is wide and flattened. Due to these traits it is possible that Palaegama leaped from tree to tree prior to the addition of lateral membranes stiffened with fibers.
Carroll (1975, 1977)
understood that Palaegama might have had a role in the origin of lizards, but those publications preceded computer-assisted phylogenetic analysis and Carroll was not aware of the pre-squamate and tritosaur clades, nor did he make the connection to Coelurosauravus.
A large gamut cladogram is ideal for solving many such problems.
Carroll RL 1975. Permo-Triassic ‘ lizards ’ from the Karroo. Palaeontologia africana 18, 71–87.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.