SVP 6 – Aphanizocnemus, a pre-snake or a skink?

Campbell, Caldwell and Dal Sasso 2015 discuss Aphanizocnemus, which nests as a pre-snake in the large reptile tree.

Figure 5. Aphanizocnemus libanensis, previously considered a dolichosaur, here recovered between Jucaraseps and Adriosaurus. Prior snake studies did not include Jucaraseps, a key taxon.

Figure 1. Aphanizocnemus libanensis, previously considered a dolichosaur, here recovered between Jucaraseps and Adriosaurus. Prior snake studies did not include Jucaraseps, a key taxon. Click to enlarge.

From the abstract:
“Aphanizocnemus libanensis is a small monotypic lizard from platy limestones deposited in patch reef lagoons stretching across the Tethyan platform from North Africa to Europe (Cenomanian; Upper Cretaceous). The sole specimen is articulated and nearly complete, though the skull was destroyed during collection. The original description placed the taxon within the Varanoidea as a member of the aquatic Dolichosauridae. Reexamination suggests that characters cited as supporting varanoid-dolichosaur affinities are misinterpreted, i.e., an intramandibular joint, a character diagnostic of pythonomorphs (the group including the Dolichosauridae, Serpentes and the Mosasauria), is actually a break in the dentary associated with the considerable damage to the skull. The single frontal omits this animal from the Varanoidea, which have paired frontals, and the shape of the frontal-nasal suture indicates that the nasals are broad and robust, unlike the splint like condition seen in dolichosaurs. In addition, though we recognize variability in the shape of the parietals of dolichosaurs, the exceptionally large parietal of Aphanizocnemus is far wider and more extended than seen in any dolichosaur, which have posteriorly narrowed parietals far longer than they are wide. The morphology of the scapulocoracoid (rounded, semicircular) and the neural spines (low, posteriorly directed) are common to many squamates, and like many other features of the specimen, i.e., the unfused, simple girdles; the reduced, flattened limbs; the shorter hind limb; and the poorly ossified tarsus, are likely tightly linked to aquatic adaptation. The hallmark feature of the specimen is the strongly regressed tibia, which is short and flat, with unclear articular surfaces. Limb reduction is a characteristic of the Pythonomorpha, but it is also common to numerous families within Squamata, including the Scincomorpha. We hypothesize here that the genus Aphanizocnemus is not a varanoid, nor in fact an anguimorph, but may represent a new form of aquatic scincomorph, a group not previously recognized as having evolved aquatic adaptations.”

Nice to get confirmation here.
Indeed Aphanizocnemus is not a varanoid nor a member of the Pythonomorpha nor, (contra the abstract) a member of the skink/amphisbaenid clade. To shift Aphanizocnemus to the skinks or varanids adds a minimum of 26 steps in the large reptile tree. Despite the fused frontals (an autapomorphy) Aphanizocnemus is a pre-snake nesting between tiny terrestrial Jucaraseps and larger aquatic Adriosaurus in the large reptile tree.

In correspondence with Dr. Caldwell
he does not like the connection of pre-snakes to pre-gekkos recovered in the large reptile tree. preferring varanoid lizards. Unfortunately, when you test them all together, nothing else nests more parsimoniously. Snake/gekko cladograms have been produced and collected here. I’m not saying that snakes arose from geckos, but they did have a common ancestor exclusive of any other squamate clades.

Campbell et al. need to run the phylogenetic analysis and not let minor autapomorphies throw throw them off course.

References
Campbell M, Caldwell M Dal Sasso C 2015. Re-evaluation of Aphanizocnemus libanensis – to be or not to be a dolichosaur.

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2 thoughts on “SVP 6 – Aphanizocnemus, a pre-snake or a skink?

  1. Hi Dave,

    The sister group of snakes (Ophidia), as has been thoroughly shown and strongly supported by multilocus phylogenetics, is Iguania+Anguimorpha (e.g: Wiens et al. 2012, DOI: 10.1098/rsbl.2012.0703). Along with snakes, both of them make up theToxicofera clade. Gekkos branch off very early in the squamatan tree, away from snakes and the other toxicoferans. I doubt it is appropiate to claim with such a conviction that phylogenetic trees reconstructed with over 40 genes should be ignored

    Regards

    • Genes are important, no doubt. But they also nest turtles with archosaurs and morphologically that just does not happen. So there appears to be a disparity — sometimes — between morphs and genes. I can only present what the computer recovers regarding morphology and I have to ignore genetic testing. The occasional disparity between the two is the current ‘dark matter’ puzzle of paleontology. Thanks for writing, Andres.

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