The Traditional Reptilia
Paleontologists have traditionally assumed that all the animals we commonly refer to as “reptiles” (lizards, snakes, turtles, crocs, the tuatara and all their prehistoric ancestors) were monophyletic, descending from a single ancestor and forming a single clade, the Reptilia (Modesto and Anderson 2004). Birds were added to this group, having descended from the dinosaurian sisters of crocodile ancestors. In this hypothesis the mammals and their ancestors (collectively the Synapsida) were not considered reptiles because they were thought to have branched off the family tree earlier.
The Traditional Amniota
Traditionally, mammals (and their ancestors) joined birds, crocs, lizards, turtles (and their ancestors) in a monophyletic clade, the Amniota. All these taxa share a trait derived from a common ancestor, an amnion, an embryonic membrane that protects the embryo during development whether an egg shell is present or not.
Purported outgroup taxa
Various diadectids and microsaurs were said to nest just outside the Amniota. According to tradition, these “reptile-like amphibians” must have laid their eggs in water and produced tadpoles because they were thought to precede the development of the amnion. It didn’t seem to matter what sort of evolutionary mismatches resulted. Diadectids and microsaurs certainly do not share many traits with each other.
Now these traditions have been changed, according to the results of a very large cladistic analysis, unprecedented in scope.
Just like a larger telescope brings greater resolution to astronomical images, a larger cladistic analysis brings greater resolution to family trees. No one had ever created a cladistic analysis that included basal representatives from the gamut of the Amniota until now. All prior analyses used smaller inclusion sets based on assumption and tradition. Many recovered poorly resolved trees with poorly matched purported sisters sharing few traits.
The present analysis recovered a single tree from over (the number continues to grow) 235 specific and generic taxa with all reptiles (including synapsids) descending from the “pre-reptile” Gephyrostegus (see below). All sister taxa share many traits and greatly resemble one another. The tree solves many prior mysteries and nests several former enigmas.
A Big Surprise
The new tree produced two major reptilian branches before the advent of any known reptile fossils. Thus, there was not a single basal reptile (defined here as “without a discrete intertemporal bone”). These two major branches go by old names: the Lepidosauromorpha and the Archosauromorpha because one branch includes lepidosaurs and the other branch includes archosaurs. The second branch also includes mammals and their ancestors.
Tiny Origins
As Carroll (1970) predicted, the most basal known reptiles, Cephalerpeton and Casineria, were indeed tiny, but not as tiny as the last of the pre-reptiles (one of which would have been the sister to the last common ancestor of Cephalerpeton and Casineria, and thus would have been the first reptile/amniote).
Goodbye Amniota
Now several reptiles (including Casineria, the microsaurs, and at least four protosynapsids) precede the branching of the Synapsida. That means the Reptilia = the Amniota. Since the former term precedes the latter, the Amniota has now become redundant, no longer distinct from the Reptilia.
These results shift taxa around like branches on a fake Christmas tree.
Diadectids and microsaurs join the Reptilia. Caseids leave the synapsids. Mesosaurs join the ichthyosaurs. We have a new basal dinosaur family tree. We’ll talk about other details in future blogs, or you can read them for yourself now at reptileevolution.com.
What does this have to do with pterosaurs?
Everything. This is the study that nested pterosaurs with lizards, specifically with a new, previously unidentified third squamate clade, the Tritosauria, originating with Lacertulus in the Late Permian. Breaking paradigms left and right, this new tree invalidates such clades as the Ornithodira, the Avemetatarsalia and several others that included pterosaurs with dinosaurs in their definitions.
More later.
Figure 1. Click to enlarge. The new, diphyletic tree of the Reptilia (= the Amniota)
As always, I encourage readers to see the 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.
References:
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165. doi:10.1098/rstb.1967.0006
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Jaeckel O 1902. Über Gephyrostegus bohemicus n.g. n.sp. Zeitschrift der Deutschen Geologischen Gesellschaft 54:127–132.
Modesto SP and Anderson JS 2004. The Phylogenetic Definition of Reptilia. Systematic Biology 53(5):815–821. DOI: 10.1080/10635150490503026
The Pterosaur Heresies 
Since when Synapsids are archosauromorphs? PFFFF
July 31, 2011. Here’s the announcement based on adding previously omitted taxa. This has not changed in the last 12 years. https://pterosaurheresies.wordpress.com/2011/07/31/the-big-kahuna-the-reptilia-is-diphyletic/
Why do you describe Reptilia as “diphyletic”, when in fact it would be paraphyletic if your hypothesis that synapsids evolved from reptiles was true, which it wasn’t? “Diphyletic” would mean that two clades independently evolved similar traits.
Good point! In the LRT in 2012 the traditional “Reptilia” split at its inception into Lepidosauromorpha and Archosauromorpha. That was the news. I wanted to give the headline some shock value. To your point Reptilia (= Amniota) is and always has been monophyletic based on the egg, not morphological traits. At the time Silvanerpeton was either the outgroup or the last common ancestor. I used this headline to emphasize the initial split, a novel hypothesis that has not been tested since then by other workers with a similar taxon list. Curious: what would have been a better headline given what the LRT recovered back then? Perhaps a change is appropriate.
Your fringe ideas like synapsids being reptiles have nothing to do with the Lepidosauromorpha-Archosauromorpha split.
Also, if this article is really about the Lepidosauromorpha-Archosauromorpha split, it does not deserve a clickbait headline. It’s also not extraordinary. Every clade is supposed to be divided into two. If being divided into two clades make a group diphyletic, than all clades are diphyletic, and diphyly is a sign that you are classifying organisms correctly.
That is not the case. “Diphyletic” means a group consists of two different monophyletic/paraphyletic groups, which aren’t related (in the way that counts), making it polyphyletic.
Old World vultures and ravens are two examples of diphyletic groups. Old World vultures consist of Gypaetinae and Aegypiinae, two subfamilies of Accipitridae whose common ancestor wasn’t a vulture. And ravens consist of the Corvus corax complex and the clade consisting of the Australasian ravens, two clades of crows whose common ancestor wasn’t a raven.
Amniota is not diphyletic. It consists of two clades, Synapsida and Reptilia, which share a common ancestor that was an amniote. Even if your view that synapsids are archosauromorphs is true, Lepidosauromorpha and Archosauromorpha presumably share a common ancestor that was a “reptile”.
True. I thought I made that clear. Reptilia = Amniota. Silvanerpeton is the last common ancestor and therefore a reptile (Amniota is a junior synonym).
This is a 2011 headline (based on 235 = a tenth of the present number of taxa), subject to freshman naiveté in all regards. That means I did not know then what I know now. From the start the lizard + turtle clade was different from the archosaur + mammal clade. This recovery was also a discovery that overturned then and current paradigms. The headline is click-bait in hindsight only. At the time it seemed worthy. That’s because I did not know better.
PLUS (very important PLUS): Silvanerpeton is not mentioned in the text because it had not yet been added to the tree at that time. I was – and am – learning as I go. Understanding has grown since then in all regards. Every day I learn something new.
Even so… mammals continue to be reptiles, closer to birds and alligators than lizards + turtles with 10x more taxa. No one has tested this hypothesis since it was proposed over a decade ago. This is part of the traditional pattern in paleontology: a curious lack of curiosity and an urge to shut out all hypotheses that don’t agree with college courses – especially from those who didn’t pay for college courses. Remember it took over a century for PhDs to acknowledge that birds were theropod dinosaurs after the initial ‘fringe idea’.
All you (yes, you, lyrebird333) have to to do to test this hypothesis is to add more taxa than you have read about in out-dated textbooks. Cherry-picking taxa and taxon exclusion continues unabated and without remorse out there, as you just demonstrated. Tell me what you know from experimentation, not what you know from casual reading. Get back to us after you have repeated the experiment using a similar taxon list. If I could do it with so little understanding in 2011, you can do it with your present understanding in 2023.
Thank you for bringing this topic up. Perhaps this reply to your comment will clear up this issue.