Testing pterosaur ingroup and outgroup relationships: Baron 2020

Matthew Baron 2020 brings us
a massively flawed view of pterosaur in-group and out-group relations. The flaws are due to taxon exclusion.

Baron holds onto the tradition nesting pterosaurs with archosaurs creating the invalid clade “Ornithodira“. He writes, the omission of other ornithodirans and avemetatarsalians has the potential to adversely affect the results of phylogenetic analyses.”

That should have been a red flag. In Peters (2000, 2007) the large reptile tree (LRT, 1714+ taxa) small furry pterosaurs with long fingers and toes arise from small furry lepidosaurs (Fig. 1) with long fingers and toes. In the LRT deletion of clades rarely affects tree topology. Those lepidosaurs were ignored by Baron 2020.

Baron ignores some of the peer reviewed literature when he writes,
no transitional non-flying pterosaur taxa are known (though some specimens have been suggested to be exactly that)”.

Outgroups in Baron 2020 include massive and non-volant Postosuchus + Herrerasaurus and smaller non-volant Marasuchus and Lagerpeton.

To his credit, Baron 2020 notes,
“The purpose of outgroup taxa is to reflect, as best as is possible, the ‘basal’ condition for the ingroup clade being studied—it is arguable that this is not the case in the analyses by Britt et al. (2018) and Dalla Vecchia (2019) and that these analyses fall short in this key respect.” and “Other studies of early pterosaur interrelationships have similar shortcomings in terms of the outgroup taxa sampling.”

To his discredit, Baron notes, 
“While Scleromochlus taylori was considered as a possible close relative of pterosaurs at the time Kellner (2003) was published, subsequent work on this taxon has demonstrated that it is more likely an archosauriform belonging to the clade Doswelliidae (see, Bennett, 2020). 

Suggestion: keep adding taxa until Scleromochlus stops moving around. That will happen when you add several small, bipedal crocodylomorphs.

Figure 1. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown.

Figure 1. Bergamodactylus compared to Cosesaurus. Hypothetical hatchling also shown. Makes more sense than Postosuchus or Marasuchus.

Looking for lost keys where no one dropped them, Baron writes,
“This study aims to test what effect, if any, the omission of such close pterosaur relatives from analyses has had on the overall topology within Pterosauria, Britt et al. (2018) and Dalla Vecchia (2014, 2019) could be resolved through a simple addition of better and more appropriate outgroup taxa, and this is what this study attempts to do. By also incorporating new anatomical characters, taken from recent early dinosaur and archosaur studies, this study aims to better anchor the base of Pterosauria to a position within Avemetatarsalia and Ornithodira, so as to allow the ‘basal’ condition of pterosaurs to be better expressed in the data.”

None of the taxa recovered as pterosaur ancestors
by Peters 2000 (e.g. Langobardisaurus, Cosesaurus, Sharovipteryx and Longisquama) were mentioned in Baron 2020 fulfilling Bennett’s curse, “You will not be published, and if you do get published, you will not be cited.” We can also blame a long list of pterosaur workers acting as referees for keeping these taxa off of Baron’s radar, compelling him to use some useless (for these purposes) archosauriforms and archosaurs.

Baron’s initial cladogram is completely unresolved
at the base, both within and outside the Pterosauria. The LRT does not have that problem. In addition, Baron’s taxon list includes way too few taxa relative to the large pterosaur tree (LPT, 250 taxa) and fails to recover four distinct pterodactyloid-grade clades.

Baron’s second cladogram resolves the outgroup problem
and recoveres the small theropod, Marasuchus, and the proterochampsid, Lagerpeton, as outgroup taxa. Both have a vestige pedal digit 5, which makes evolving a lepidosaur-like long pedal digit 5 in basal pterosaurs impossible. Neither preserves a skull, which is a problem, especially when good skulls are known for Langobardisaurus, Cosesaurus, Sharovipteryx and Longisquama and these share many traits with basal pterosaurs (Fig. 1).

The basalmost pterosaur in the LRT and LPT,
Bergamodactylus (MPUM 6009, Fig. 1) is not mentioned in the Baron 2020 text.

Baron’s discussion includes the phrase,
much work needs to be done to further broaden the datasets used in phylogenetic analyses, in terms of both the operational taxa and anatomical characters and character states.”

Actually that work has already been done. As a resut, so much taxon exclusion in Baron’s  2020 study means it was a complete waste of the author’s time, efforts and expense. Add taxa, Matthew Baron, and all the problems created by your colleagues will disappear with complete resolution. 

Which raises the final question,
How long is the sort of taxon and literature exclusion described above going to keep appearing in the literature? Add taxa. That’s all the LRT and LPT keep telling us.

Figure 7. Subset of the LPT focusing on Triassic pterosaurs.

Figure x. Subset of the LPT focusing on Triassic pterosaurs.

Baron MG 2020. Testing pterosaur ingroup relationships through broader sampling of avemetatarsalian taxa and characters and a range of phylogenetic analysis techniques. PeerJ 8:e9604 DOI 10.7717/peerj.9604
Huene Fv 1914. Beiträge zur Geschichte der Archosaurier. Geologische und paläontologische Abhandungen, NF 13:3–53.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.


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