What would snakes be, if Pan-ophidians were not known?

This is lesson 2 in taxon exclusion…
to see where select clades would nest in the absence of their proximal taxa.

Ophidians (Pan-serpentes) are all squamates closer to snakes (clade = Serpentes) than to other living groups of lizards. More narrowly, according to Wikipedia, “Ophidia was defined as the “most recent common ancestor of Pachyrhachis and Serpentes (modern snakes), and all its descendants” by Lee and Caldwell (1998: 1551).”

We’re going to introduce the term to Pan-Ophidia
for all clade members in the lineage of snakes (= closer to snakes than to other living groups of lizards). Clade members of the Ophidia are somewhat different in the large reptile tree (LRT, 1142 taxa, subset Fig. 1). Here the Ophidia currently begins with Norellius and includes Ardeosaurus, Eichstaettisaurus, Pontosaurus, Tetrapodophis, Dinilysia and their kin, with a sister clade among the ancestors to geckos.

Figure 2. Subset of the large reptile tree focusing on lepidosaurs and snakes are among the squamates.

Figure 1. Subset of the large reptile tree focusing on lepidosaurs and snakes are among the squamates.

Since we have access to the large reptile tree
(LRT, 1242 taxa) which lets us play around with deletions (taxon exclusion) let’s see where snakes (Dinilysia + Pachyrhachis + living snakes) would nest in the absence of ophidians (and Archosauromorpha). At the base of snakes is the basal burrowing snake, Loxocemus. Outgroups include the clade Heloderma + Lanthanotus and the clade Anniella + Gobiderma. This clade nests between Shinisaurus and the Ophisaurus clade + skinks. Moreover, the rest of the Squamata breaks into 14 clades without resolution, among them the geckos and varanids.

Deleting all geckos (sisters to the Pan-Ophidia in the LRT) returns complete resolution to the remainder of the tree, and snakes still nest with the clades listed above, not with varanids or mosasaurs.

Deleting Dinilysia + Pachyrhachis
not only loses resolution within snakes, all proximal outgroup taxa also lose resolution. Outgroups also include the skinks + amphibaenids

When the gekko clade is included again,
does not improve the situation. No wonder snakes have been so difficult to nest, in the absence of the proximal taxa listed in figure 1.

Taxon exclusion
has been the number one problem in traditional paleontology. That’s why the LRT includes such a wide gamut of taxa. The result is a minimizing of taxon exclusion and the problems that attend it.

More traditionally (and due to taxon exclusion)
Wikipedia reports, “There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, such as the varanids (or a similar group) during the Cretaceous Period. This hypothesis was strengthened in 2015 by the discovery of a 113m year-old fossil of a four-legged snake in Brazil that has been named Tetrapodophis amplectus. It has many snake-like features, is adapted for burrowing and its stomach indicates that it was preying on other animals.”

Taxon exclusion
has been the number one problem in traditional paleontology. That’s why the LRT includes such a wide gamut of taxa. The result is a minimizing of taxon exclusion and the problems that attend it.

References

https://en.wikipedia.org/wiki/Ophidia

https://en.wikipedia.org/wiki/Snake

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