Here’s another case of an inadequately small inclusion set mistakenly nesting a taxon far from its most parsimonious nesting site. Today we look at Lanthanolania, described earlier (Modesto and Reisz 2002) as a sister to Planocephalus, and recently (Reisz and Modesto 2011) as a sister to Orovenator (Figure 1). New postcranial material (which has not yet been published) sets it apart as the oldest known bipedal diapsid.
Figure 1. Lanthanolania and its sisters. Orovenator does not belong.
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 added a minimum of 20 steps.
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 (taxa related to Petrolacosaurus) and Eudibamus, a true diapsid, is 25 million years older (if it was a biped as often described). On the other hand, two Lanthanolania sister taxa, Palaegama and Saurosternon, both have proportions similar to those of bipedal lizards. I am eager to see the post-crania of Lanthanolania to see if there are any clues in the ribs. pelvis and feet demonstrating affinity to the Triassic gliders.
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.
References:
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Reisz RR and Modesto SP 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles.SVPCA abstract published online.
The Pterosaur Heresies 