The kuehneosaurids, arboreal gliding lepidosauriforms, have an interesting pedigree. Tradition holds that they appeared suddenly without precedent and, until recently, only two genera were recognized, Icarosaurus and Kuehneosaurus (Fig. 1), both from the Late Triassic. By contrast, the large reptile tree found an extended evolutionary lineage that we looked at earlier. Here we’ll look at the skulls in sequence, talk about the new kuehneosaur, Pamelina, and discuss the reptile family tree.
Gliding struts and lateral extradermal membranes probably first appeared as decorations because the skull of Coelurosauravus (Fig. 1) is also distinctly decorated with a squamosal/supratemporal frill. Mecistotrachelos (Fig. 1) kept its frill. The others did not. The frill-less taxa also lose the supratemporal, a bone that makes up the back part of the frill. Palaegama has no dermal struts. Lanthanolania is known by a skull only. Pamelina vertebrae (Fig. 2) do not have the long fused transverse processes of Kuehneosaurus.
Widely considered to glide with hyper-elongated ribs, the lineage of kuehneosaurids indicates that those ribs were actually ossified dermal filaments/bones (as seen in Coelurosauravus, Fig. 1). The ribs shrank (Fig. 2) and disappeared and in their place grew elongated transverse processes to act as anchors for the gliding struts. This happened by convergence twice, once in Mecistotrachelos and again in the lineage of kuehneosaurids without a frill. You can see the transformation in Kuehneosaurus and Pamelina (Fig. 2).
A paper by Evans (2009)
described Pamelina (Fig. 1), an early Triassic kuehneosaurid added a third genus to her list of kuehneosaurs. Note the lack of fused transverse processes on the dorsal vertebrae in Pamelina. The elongated caudal transverse processes indicate the presence of a large caudofemoral muscle, which would have been much smaller in Kuehneosaurus.
Earlier we also added Xianglong (which is not a lizard), and Lanthanolania (which is not a younginoid) along with Coelurosauravus (Fig.1), which everyone else thinks developed rib membranes by convergence.
Evans (2009) produced an interesting family tree of the Reptilia. Except for turtles it splits reptiles into two main lineages, one that includes lepidosaurs and one that includes archosaurs, like the large reptile tree does. Of course the tree by Evans assumes the outgroups and basal taxa include synapsids, which nest in the archosaur half of the large reptile tree.
The current state of phylogenetic thinking
Evans (2009) reports, “The Neodiapsida of Benton (1985) encompasses a wide range of diapsid lineages, most of which can be assigned to either Archosauromorpha or Lepidosauromorpha (Gauthier et al. 1988). Archosauromorpha encompasses a large and successful crown clade (Archosauria) and a series of distinctive stem lineages (e.g., protorosaurs, tanystropheiids, Prolacerta, Rhynchosauria, Trilophosauria, Evans 1988; Gauthier et al. 1988; Müller 2002, 2004; Modesto and Sues 2004). Crown−group Lepidosauria (Rhynchocephalia and Squamata) also constitutes a large and diverse group but, leaving aside the issue of testudine or sauropterygian affinities (e.g., Rieppel and de Braga 1996; de Braga and Rieppel 1997; Rieppel and Reisz 1999; Müller 2002, 2004; Hill 2005).”
By contrast the large reptile tree found those listed members of Evans’ “Neodiapsida” to be diphyletic and found the lepidosauromorpha also include tanystropheids, Rhynchosauria and Trilophosauria along with turtles.
We’re working for consensus, but first others have to expand their inclusion set gamut and avoid suprageneric taxa.
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.
Evans SE 2009. An early kuehneosaurid reptile from the early Triassic of Poland. Palaeotologia Polonica 65: 145-178.