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Stem geckos? Or stem snakes? – SVP abstract 2016

Friday, October 28, 2016 12:43
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(Before It's News)

Earlier Simoes et al. 2016 published their paper and today their SVP abstract of Eichstaettisaurus and Ardeosaurus, two Jurassic squamates. Here’s how the LRT (subset Fig. 1, complete tree here) recovered geckos, snakes and stem snakes like Eichstaettisaurus and Ardeosaurus, the dual subjects of Simoes et al. 2016 paper and abstract.

Figure 1. Subset of the LRT focusing on geckos snakes and stem snakes that nest close to geckos.

Figure 1. Subset of the LRT focusing on geckos snakes and stem snakes that nest close to geckos.

From the Simoes et al. 2016 abstract:
“Late Jurassic lizards from Solnhofen, Germany, are some of the oldest known articulated lizard specimens in the world (1), and are also the most complete Jurassic squamates. These specimens are thus very important to our understanding of early squamate evolution, with valuable information regarding morphology, taxonomy, and phylogeny. Eichstaettisaurus schroederi and Ardeosaurus digitatellus are two of the best  preserved species from that locality, the former being represented by the most complete Jurassic lizard specimen known anywhere in the world. Despite their relevance to broad questions in squamate evolution, their morphology has never been described in detail, and their systematic placement has been under debate for decades. Here, we provide the first detailed morphological description, species level phylogeny and functional morphological evaluation of E. schroederi and A. digitatellus. We identified previously undescribed features of E. schroederi linking this taxon to gekkotans, such as the Meckelian canal being closed and fused medially, ectopterygoid lying dorsal to transverse process of pterygoid, and autopodial digit symmetry. Using a revised and updated dataset containing 610 characters and 193 taxa (2), we corroborate their initial placement as geckoes—stem gekkotans, more specifically. This is of fundamental importance to the early evolution of squamates, as it demonstrates the existence of yet another major extant squamate clade (Gekkonomorpha) in the Jurassic (3). Additionally, both taxa illustrate a number of climbing adaptations (e.g. shape of unguals, penultimate phalanges, and body proportions), which indicates a scansorial lifestyle arose earlier in the evolution of geckos than previously known. Autopodial modifications associated with digital hyperextension and adhesive toepads (e.g. depressed and reduced intermediate phalanges, and arcuate penultimate phalanges), which provide geckoes with a highly sophisticated climbing apparatus, are not present. Therefore, our findings further suggest that morphological adaptations for scansoriality evolved in geckoes prior to the first known occurrence of adhesive toepads in the Cretaceous. Our results provide support from the fossil record to most molecular and combined evidence estimates of the origin of most major clades of squamates, including geckoes, which usually place divergence times for their stem back in the Jurassic or the Triassic.”

Figure 1. From Simoes et al 2016, their cladogram of the squamates separate varanids from mosasaurs, link snakes to skinks and shows how close pre-snakes are to basal geckos.

Figure 1. From Simoes et al 2016, their cladogram of the squamates separate varanids from mosasaurs, link snakes to skinks and shows how close pre-snakes are to basal geckos.

Notes

  1. In the LRT lepidosaurs extend back to the Early Permian (TA 1045 specimen, close to Saniwa) and Lacertulus (Late Permian).
  2. The Ardeosaurus/Echstaettisaurus clade lies outside the geckos, inside the Pro-serpentes in the LRT as a single clade, but 3 ways by Simoes et al.
  3. No wonder those two taxa form a separate clade outside the geckos in the Simoes et al. report. The do so as well in the LRT, at the base of all snake and pro snakes.
  4. The LRT is a single, fully resolved tree, not the consensus of 3174 MPTs.

References
Simoes TR, Caldwell MW, Nydam RL and Jimenez Huidobro P 2016. Osteology, phylogeny and functional morphology of two Jurassic lizard species indicate the early evolution of scansoriality in geckoes. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Simões TR, Caldwell MW, Nydam RL and Jiménez-Huidobro P 2016. Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12487 http://onlinelibrary.wiley.com/doi/10.1111/zoj.12487/fullwiki/Ardeosaurus

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