Lanthanolania ivakhnenkoi (Modesto and Reisz 2003) Late Permian ~265 mya ~2.5cm skull length was originally considered a sister to Planocephalosaurus and the Squamata. A more recent analysis by Reisz and Modesto (2011) that included nearly a complete post cranial skeleton nested Lanthanolania with the younginid, Orovenator. I haven't seen their analysis, but the present analysis nests Lanthanolania with the gliding lepidosauromorphs, Coelurosauravus, Icarosaurus, and Kuehneosaurus, close to Saurosternon and Palaegama, with which it was not previously tested against. Moving Lanthanolania close to Orovenator adds a minimum of 20 steps. See image below.
Distinct from Palaegama, the skull of Lanthanolania was relatively shorter with a taller orbit. The rostrum was convex and the ascending process of the maxilla expanded dorsally. The lacrimal was larger. The postorbital was larger. The palate was nearly identical to that of Kuehneosaurus. The skull in ventral view was also similar in shape.
Limb proportions mentioned by Reisz and Modesto (2011) suggest Lanthanolania might have been the oldest known bipedal diapsid. Unfortunately Lanthanolania was not a diapsid and Eudibamus is 25 million years older. Palaegama and Saurosternon both have proportions similar to those of bipedal lizards. I am eager to see the post-crania to see if there are any clues in the ribs, pelvis and feet demonstrating affinity to the Triassic gliders.
Lanthanolania and Saurosternon nest at the base of the Lepidosauriformes, defined by Gauthier, deQuieroz and Estes (1988) as Sphenodon and squamates and all organisms sharing a more recent common ancestor than they do with younginiforms. They intended this to include Paliguana, Saurosternon, Kuehneosauridae, Rhynchocephalia and Squamates, but in the context of the present study their Lepidosauriformes would be redundant with the current Lepidosauromorpha.
Redefined, the Lepidosauriformes now includes Paliguana, Sphenodon, their most recent common ancestor and all of its descendants.
That now includes rhynchosaurs, trilophosaurs and pterosaurs which were formerly excluded.
Between Paliguana and the Lepidosauria the present cladogram looks very much like the one presented by Gauthier, deQuieroz and Estes (1988). They considered the Younginiformes to be ancestral, but that clade is unrelated according to the present larger study.
See the complete tree. |
