Updated February 22, 2015 with a new image of Tchingisaurus.
Earlier the squamate tree of life by Gauthier et al. (2012) was introduced. In large part this tree resembled the large reptile tree of reptileevolution.com. Parts of the trees were different from each other. We’ll look at some of those today and later.
The nesting of Tchingisaurus (Fig. 1) at the base of a basal scleroglossan clade that included Gilmoreteius (Macrocephalosaurus) is one such difference. Previously I had not looked at Tchingisaurus, a Cretaceous specimen known from a partial skull preserved in 3D. The Gilmoreteius clade in the Gauthier et al. (2012) paper was nested close to the base of the clade that produced Adriosaurus and mosasaurs and also close to the clade that produced Eichstattisaurus and Gekkotans.
In the large reptile tree Tchingisaurus nested as a sister to Gekko (note the shared lack of any temporal bars), also near the base of the Scleroglossa. Eichstattisaurus nested closer to Ardeosaurus and Adriosaurus. So there was a comparative switch-off between the two clades with Tchingisaurus and Eichstattisaurus nearly trading places. The large reptile tree nested the mosasaurs closer to their traditional sisters, the varanids and snakes, not the gekkotans.
Missing from the base of the Gauthier et al. (2012) tree were the basal scleroglossans Liushusaurus and Eolacerta. Also missing were the basal squamates the Daohugo lizard, Lacertulus, Meyasaurus, Tijubina, Homoeosaurus and Dalinghosaurus. Are these exclusions the cause of the differences in the two trees? And I’m not even including the third squmate clade, the Tritosauria, which we have covered earlier and I’ll touch on again later.
Only three taxa were recovered in the Iguania in the large reptile tree. I wasn’t so interested in their relationships, which I considered relatively uncontroversial, but the larger study by Gauthier et al. (2012) had little resolution at the base of the Iguania. So, maybe this clade is more mysterious and interesting than I first imagined. Or perhaps the Iguania needed to be anchored with the above named saurians.
We’ll take another look at the origin of the snakes and amphisbaenians in the next few days, noting the differences between the results recovered in the large reptile tree vs. the much larger study by Gauthier et al. (2012).
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.
Gauthier, JA, Kearney M, Maisano JA, Rieppel O and Behkke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3-308. online here.