Basal Lepidosauromorpha – the story told with skulls

Sometimes it just helps
to see a bunch of taxa together to get an appreciation for the evolution of one to another to another and another. Well, here are the members of one branch of the basal reptiles, the early plant-eaters, the new Lepidosauromorpha, all taken from the large reptile tree (recently slightly revised).

Click to enlarge. These skulls are arranged phylogenetically according to the results recovered from the large reptile tree.

Figure 1. Click to enlarge. These skulls are arranged phylogenetically according to the results recovered from the large reptile tree.

Contrary to conventional thinking,
the Diadectomorpha and Chroniosuchia are nested here within the Reptilia rather than within the pre-amniotes. Contrary to conventional thinking, the Caseasauria are nested here within the Millerettidae, rather than the Synapsida. These, and other new relationships were determined by adding taxa and thereby expanding the gamut of opportunities for every taxon to nest most parsimoniously – where the changes between taxa are minimized echoing the actual tree of reptile evolution.

Central to these discussions
Romeria primus (Fig. 1 in pink) – is at the base of the millerettids that begat the bolosaurids, acleitorhinids (not related to Lanthanosuchus btw), and the caseasauria, which now has new basal members, Feeserpeton and Australothyris. Romeria primus was largely ignored in prior studies. Now, perhaps, its importance will no longer be overlooked.

Orobates (Fig. 1 in yellow) – is leading the way toward Tseajaia and Tetraceratops, Limnoscelis, Procolophon, the lineage of Diadectes, Chelonia beginning with Stephanospondylus, and not finally the Pareiasauria. Orobates, likewise needs to rise in importance and needs to be added to several more focused phylogenetic analyses.

Saurorictus, Macroleter and the lanthanosuchids, Romeriscus and Lanthosuchus.

Figure 2. Click to enlarge. Saurorictus, Macroleter and the lanthanosuchids, Romeriscus and Lanthosuchus.

I say not finally because the next clade includes Saurorictus and Nyctiphruretus (Fig. 2) and the remainder of the new Lepidosauromorpha, including lanthanosuchids (Fig. 2), owenettids and the Lepidosauriformes.

No strange bedfellows here.
All taxa demonstrated gradual transitions from one to another. With this new phylogeny and tree topology the taxa that may or may not be someday discovered can more accurately be predicted based on phylogenetic bracketing. Hopefully more discoveries will help find the sisters of Orobates that will help define the base of this new, hitherto unknown clade.

Not amphibians!
Hopefully readers will glean the important fact that limnoscelids, chroniosuchids and diadectids are not amphibians (pre-amniotes), which represents conventional thinking. No, they’re nested deep within the Reptilia, far from Gephyrostegus and its ancestors and their kin.

Eudibamus is notably absent
Because Eudibamus is not a bolosaurid. It is a basal diapsid close to Petrolacosaurus. Strong foot homologies and long suite of other traits nest it there, not with heavy, plant-eating bolosaurids.

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.

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