Traditional paleontologists insist on nesting pterosaurs with archosaurs, despite no evidence to support such a relationship. Well, two can play at that game.
I took the large reptile tree and separated the two halves in PAUP (deleting first one branch, then the other). Then I took one taxon at a time from one branch and force nested it within the other branch. Here I’ll report the results. We’ll start with the pterosaur, MPUM 6009, which earlier nested with turtles (also force misnested) and sauropterygians, not where traditional paleontologists presumed.
ALL of the nestings will seem odd. That’s because they don’t belong there!
Placing a new lepidosauromorph within the new Archosauromorpha clade
The basal pterosaur MPUM 6009 nested with Pachypleurosaurus, a basal sauropterygian, far from the basal archosaurs pterosaurs have been traditionally force nested with.
What Does This Study Tell Us?
First of all, this study demonstrates that any taxon will nest in any other clade by default. It will not resemble its putative sisters, but it will find a place nevertheless. That’s why it’s so important to take a step back after recovering tree results and looking for mismatches among putative sisters. Again, pterosaurs don’t belong with archosaurs. Strangely they nest with basal sauropterygians when the taxon list deletes nearly all of the new Lepidosauromorpha, as demonstrated by testing. With those deletions and exclusions they nest most parsimoniously with tritosaur fenestrasaur lizards, a clade that demonstrates a gradual accumulation of pterosaurian traits.
A priori assumptions, based on tradition rather than phylogenetic testing run the same accidental risk with their taxon lists that we just played out on purpose. No phylogenetic testing should be considered valid unless some sort of overarching study has set the parameters for taxon inclusion and exclusion. All sister taxa should look like each other. A gradual accumulation of derived traits should be present for all taxa.
Earlier views that placed rhynchosaurs and trilophosaurs with basal archosauriforms and protorosaurs did so only in the absence of more parsimonious sister taxa. Earlier views that placed caseids with synapsids suffer from the same problem. The list of mistakes in traditional nesting is long. This blog will continue to point out bad nestings due to taxon exclusion as they occur, supported by the large (and growing larger) reptile tree.
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.