What would pterosaurs be, if tritosaurs were not known?

This is lesson 4 in taxon exclusion…
to see where select clades would nest in the absence of their proximal taxa.

Now that
the large reptile tree has grown more than three fold in the last seven years, it’s time to ask (or ask again) some phylogenetic questions.

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

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

pterosaurs are nested with archosauriformes, like Scleromochlus, close to dinosaurs, but only in the absence of fenestrasaurs and tritosaurs. In the large reptile tree (LRT, 1242 taxa), which includes representatives from all tetrapod clades, pterosaurs nest with fenestrasaurs (Peters 2000) and tritosaur, lepidosaurs (not prolacertiformes (contra Peters 2000, who did not test Huehuecuetzpalli, which came out in 1998).

In the absence of tritosaurs (and Archosauromorpha)
pterosaurs nest with drepanosaurs, both derived from Jesairosaurus.

In the absence of tritosaurs (and Lepidosauromorpha)
pterosaurs nest between Mei and Yi among the scansoriopterygid birds (Fig. 2) which are derived from Late Jurassic Solnhofen bird taxa, too late for the Late Triassic appearance of pterosaurs like Bergamodactylus (Fig. 1).

Figure 1. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.

Figure 2. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.

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.

Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

4 thoughts on “What would pterosaurs be, if tritosaurs were not known?

  1. My hypothesis- this argues that your matrix is coding more for general proportional similarity as opposed to detailed homologous structures. Pterosaurs group with gracile birdy taxa in your matrix, whereas in a matrix like Nesbitt’s there are all kinds of braincase, carpal, trochanter, tarsal, etc. details that would not let pterosaurs be in Theropoda.

    • I think you missed the point. Nesbitt excluded taxa. I did not. Back in Peters 2000 I added taxa to prior analyses that excluded fenestrasaurs and recovered new tree topologies. Hone and Benton 2007-2008(9) excluded taxa and also messed up. To your point, I do look at proportions and ratios, but also get into bones and sutures.

      • Your ‘point’ is a fictional idea you have that taxon inclusion fixes everything in a 228 character matrix. Yes, taxon exclusion may be a problem, but if your character list is good enough it doesn’t have to be. If pterosaurs are so clearly lepidosauromorphs and you have a good character list, shouldn’t deleting (other) lepidosauromorphs leave pterosaurs sister to archosauromorphs?

        If they instead jump to paravian theropod dinosaurs, doesn’t that mean that your character list missed a ton of archosauromorph, archosauriform, archosaurian, avemetatarsalian, dinosauriform, dracohortian, dinosaurian, saurischian, theropod, avepod, tetanurine, coelurosaur, tyrannoraptoran, maniraptoromorph, maniraptoriform, maniraptoran, paravian, etc. characters?

      • Taxon inclusion also fixed everything 4x in Peters 2000. Which has been ignored ever since. When you say, “should” you’re coming at things with preconceptions. Don’t. Let the numbers do their thing. In this case Dimorphodon is more like Mei and Yi than any other taxon in the archosauriformes. If you recognize that as untenable, that’s good.

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