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Norellius nyctisaurops – a -very- basal pre-snake, -very- close to geckos
A new paper
by Conrad and Daza (2015) rediagnoses and names AMNH FR 21444 (Fig. 1, Early Cretaceous, ), “an important early and relatively basal lizard: (Conrad and Norell 2006).” Conrad and Daza describe the specimen as “a gecko-like basal squamate as identified by its braincase morphology.” it is tiny with a skull length of 1.5 cm. Postcrania is unknown.
Figure 1. Norellius from Conrad and Daza 2015. At upper right I highlight the ‘missing’ lacrimal in red and provide an alternate imagined rostrum based on that of sister taxa. Look closely at the pterygoid. There are tiny teeth there, the origin of pterygoid teeth in snakes!
Added to
the large reptile tree, Norelliius nests next to the Gekko clade that has Tchingisaurus at its base. Norelliius nests at the base of the clade that produced Eichstaettisaurus, Tetrapodophis and snakes, further cementing these two clades together. And it’s the fiirst good lock at the palate around this node.
Daza et al. 2013
was not able to resolve the position of AMNH FR 21444. According to Conrad and Daza, “It has large orbits, a complete postorbital bar and supratemporal arch, and a broad pyriform recess (Fig. 1). The skull is broadest at the level of the orbits and, apparently, tapered anteriorly. The lacrimal is absent; the maxilla and prefrontal form the margins of the lacrimal foramen.”
Funny thing,
they say the lacrimal is absent, and it is absent on the left with a space left over to receive it, but it appears to be present on the right (Fig. 1). Sister taxa all have a lacrimal.
Norellius is difficult to nest
as it lacks important bones at the front and back of the skull. And it nests very close the the origin of several major scleroglossan clades. In other words, it is very plesiomorphic. Nevertheless a few traits do ally it with Ardeosaurus, Eichstaettisaurus and other pre-snakes to the exclusion of other clades.
Conrad and Daza
consider Gekkonomorpha as basal within Squamata. The large reptile tree does not support this, but recovers Iguania and several other taxa as more basal (splitting off earlier). It should be noted that Conrad and Daza do not yet recognize the Protosquamata or the Tritosauria, two lepidosaur clades/grades basal to the Squamata. They haven’t added pertinent taxa to their studies, including the lepidosaurs Jesairosaurus, Macrocnemus and their kin.
Ironically
Conrad and Daza note: “Norellius nyctisaurops shows no gekkotan characteristics in its dermatocranium.” Only the braincase identifies it as a gekknomorph according to their study.
Conrad and Daza consider Norellius close to the base of Squamata (which it is not) and note, “Even so, the elongate postorbital skull, curved and elongate jugal, long postdentary part of the jaw, and very gecko-like braincase differ strikingly from the morphology seen in basal rhynchocephalians [Gephyrosaurus]. Clearly, more Jurassic and Triassic squamates are needed to help bridge the morphological gap between basal lepidosaurs and modern Squamata.” The large reptile tree provides several taxa to fill this purported gap. Again, the conclusions of Conrad and Daza appear to be based on taxon exclusion. The large number of pertinent taxa in the large reptile tree provide a gradual accumulation of derived characters.
Pterygoid teeth!
Look closely at the pterygoid of Norellius. There are tiny teeth there, the origin of large pterygoid teeth in snakes! Mosasaurs grew those pterygoid teeth convergently, hence the confusion with Pythonomorpha, another invalid clade (snakes + mosasaurs, Cope 1869).
References
Conrad JL and Daza JD 2015. Naming and rediagnosing the Cretaceous gekkonomorph (Reptilia, Squamata) from Öösh (Övörkhangai, Mongolia). Journal of Vertebrate Paleontology 35:5, e980891
Conrad JL and Norell MA 2006. High-resolution x-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öosh ( €Ov€orkhangai; Mongolia). Historical Biology 18:405–431.
Daza JD, Bauer AM and Snively E 2013. Gobekko cretacicus (Reptilia: Squamata) and its bearing on the interpretation of gekkotan affinities. Zoological Journal of the Linnean Society 167:430–448.
Source: https://pterosaurheresies.wordpress.com/2015/09/20/norellius-nyctisaurops-a-very-basal-pre-snake-very-close-to-geckos/
