Eichstattisaurus. Not a Gekkotan. A Snake Ancestor.

Eichstattisaurus and its sister, Ardeosaurus, were two small lizards found in Solnhofen limestones from the late Jurassic period, approximately 150 mya. Originally (Meyer 1860) and subsequently (Mateer 1982) these two were considered basal gekkotans, relatives of the living gecko, Gekko. Not much attention has been paid to either one. Both are typicall preserved complete and articulated, sometimes with some scalation and soft tissue preservation.

Eichstattisaurus and Ardeosaurus.

Figure 1. Eichstattisaurus and Ardeosaurus. Two Jurassic lizards in the lineage of snakes.

New Nesting
After entering the characters of both lizards, I was surprised to see that they nested not with Gekko, but with Adriosaurus, a hyper-elongated lizard with tiny limbs and a long neck, and Pachyrhachis, a basal snake with tiny hind limbs. This nesting, ancestral to snakes, has been largely overlooked by prior studies. I missed it too. The relationships is not obvious at first glance. I just finally got around to studying these two, fully expecting them to nest with Gekko.

Characters shared by members of this clade with Adriosaurus and Pachyrhachis include the orbit shape, the quadrate shape, supraoccipital fusion, converging temples, ectopterygoid shape, the absence of the retroarticular process, and the metatarsus configuration, among dozens of other traits that are shared with larger clades and by convergence with other reptilian clades.

The slender and elongated premaxillary ascending process was overlooked by Mateer (1982). If anyone has a palate view of either taxon, I’d like to see it.

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
Mateer NJ 1982. Osteology of the Jurassic Lizard Ardeosaurus brevipes (Meyer). Palaeontology 25(3):461-469. online pdf
Meyer H von 1860. Zur Fauna der Vorwelt. Reptilien aus dem lithographischen Schiefer des Jura in Deutschland mit Franchreich. Frankfurt-am-Main.

wiki/Ardeosaurus

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