Tikiguania Not a Triassic Squamate? No Problem! Plenty of Others!

A Rare Double Post – This Just In:
Abstract (from Hutchinson et al. 2012) – Tikiguania estesi is widely accepted to be the earliest member of Squamata, the reptile group that includes lizards and snakes. It is based on a lower jaw from the Late Triassic of India, described as a primitive lizard related to agamids and chamaeleons. However, Tikiguania is almost indistinguishable from living agamids; a combined phylogenetic analysis of morphological and molecular data places it with draconines, a prominent component of the modern Asian herpetofauna. It is unlikely that living agamids have retained the Tikiguania morphotype unchanged for over 216 Myr; it is much more conceivable that Tikiguania is a Quaternary or Late Tertiary agamid that was preserved in sediments derived from the Triassic beds that have a broad superficial exposure. This removes the only fossil evidence for lizards in the Triassic. Studies that have employed Tikiguana for evolutionary, biogeographical and molecular dating inferences need to be reassessed.

This Does Not Remove the Only Fossil Evidence for Lizards in the Triassic
…because we have a third clade of lizards, the Tritosauria, that were widespread during the Triassic. Tritosaurs include Tanystropheus, Macrocnemus, drepanosaurids, fenestrasaurs (including pterosaurs) and their kin. At the base of that clade was Lacertulus from the Late Permian.

Other basal tritosaurs include Huehuecuetzpalli, Meyasaurus and the Daohugo enigma, all from the Early Cretaceous. These demonstrate the other side of the coin for Tikiguania: late-survivor status virtually unchanged from a phylogenetic origin in the Permian or Triassic.

Oh, did I mention the tuatara, Sphenodon? The coelocanth, Latimeria? Hey guys, morphologies unchanged over tens to hundreds of millions of years can happen.

It’s Heretical, Based on a Larger Inclusion Set
Tikiguania
may be Quaternary in origin. It doesn’t matter. That doesn’t remove squamates from the Triassic. The Tritosauria, while overlooked, still counts. A larger inclusion set shows the way.

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
Hutchinson MH, Skinner A and Lee MSY 2012. Tikiguania and the antiquity of squamate reptiles (lizards and snakes). Biology Online published before print. doi: 10.1098/rsbl.2011.1216

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