Assembling the Squamate Tree of Life – part 3 – the Tritosauria and the Krypteia

Gauthier (2012) is the largest phylogenetic analysis of the Squamata. Earlier here and here we looked at various aspects of this powerful paper. Today we’ll finish up.

Unfortunately, Gauthier et al. (2012) ignored the descendants of a sister to the stem squamate Huehuecuetzpalli. The large reptile tree found the odd drepanosaurs, tanystropheids and pterosaurs were members of this previously ignored lizard clade, here called the Tritosauria. Having a large and encompassing reptile tree as a guide might have alerted Gauthier et al. (2012) to include tritosaurs, but alas, this clade was not on their radar.

Maybe someday it will be…

The Fossorial Taxa
Fossorial animals dig through dirt and are adapted to living underground. Among squamates, these include certain snakes and amphisbaenians. Gauthier et al. (2012) found that amphisbaenians and all snakes formed a natural clade, which they called the Krypteia (hidden ones).

On the other hand, the large reptile tree found amphisbaenians and dibamids nested within skinks while snakes were diphyletic, arising from two distinct varanid clades, one clade out of Heloderma and Lanthanotus and another clade of snakes out of Ardeosaurus and Adriosaurus.

As in other prior lizard/snake trees the very derived, very tiny snake, Leptotyphlops, nested at the base of all snakes in the Gauthier (2012) tree. I never understood this. Even the jaws don’t even move up and down like all other tetrapod jaws!! It’s hard to tell what’s what in Leptotyphlops with so many bones gone or fused. In the large reptile tree it’s basically the very last taxon in the new Lepidosauromorpha and more derived than the other burrowing snakes.

According to Gauthier et al. (2012) this most basal of snakes was related to a basal amphisbaenian, Spathorhynchus, despite the many basic differences. The large reptile tree recovered Spathorhynchus as a fossorial skink, distinct from all snakes.

The large reptile tree concentrated on taxa at the bases of reptilian clades and subclades in order to recover relationships. It cannot compete with the Gauthier et al. (2012) tree once one gets into the various squamate clades, but at the bases the Gauthier et al. (2012) tree lacks several key taxa that could prove to be important. From the Scleroglossa, the Gauthier et al. (2012) tree lacks Liushusaurus, Eolacerta, Yabeinosaurus, Tamaulipasaurus, Bahndwivici and Cryptolacerta.

What would their inclusion do to the Gauthier et al. (2012) tree?
It’s puzzling how such a large and carefully scored tree as the Gauthier et al. (2012) tree could arrive at so many key oddball (mis-matching) sisters. Perhaps more fossil taxa could have brought the two large trees to a closer accord.

One Last Hoohah!
Like the large reptile tree, Gauthier et al. (2012) found Estesia to nest closer to Varanus than Heloderma, confirming that the Monstersauria may be polyphyletic.

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
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.

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