Digging into another cladogram, pt. 7 (finished!)

Today’s blogpost
concludes a recent series in reducing and restoring a previously published cladogram focusing on Archosauriformes (Nesbitt et al. 2017, derived from Nesbitt 2011). Click the [previous] button above to see earlier steps in this study.

Here are several reasons
why derived rauisuchians, like Postosuchus (Fig. 1), nest with basal bipedal crocodylomorphs, like Hesperosuchus (Figs, 1, 2), in traditional cladograms, like Nesbitt et al. 2017. They really do look alike, in broad aspect and fine detail.

Figure 1. Postosuchus to scale with Hesperosuchus (Fig. 2).

Figure 1. Postosuchus to scale with Hesperosuchus (Fig. 2). Except for size, these two share a long list of traits, but the list that separates them and nests them with others is even longer.

Postosuchus and Hesperosuchus converged
on a long list of traits, from the shape of the antorbital fenestra to the crocodile-like temporal architecture in Postosuchus, distinct from other rauisuchians. Except for size (Fig. 1), these two taxa share a long list of traits, leading to prior paradigms. Here the list that separates these two taxa and nests them with other taxa is even longer when rescored and when blank scores are scored for several taxa, including Hesperosuchus.


Figure 2. Hesperosuchus, a basal bipedal crocodylomorph from the Late Triassic. Note the many traits here shared with Postosuchus (Fig. 1).

The experiment on Nesbitt et al. 2017
is finished enough. I did not examine every single matrix box, but called it quits after the topology shifted from the traditional paradigm to the LRT topology. The reduced and rescored, and too often scored-for-the-first-time 400 traits vs. 62 taxa has resulted in a tree topology different than Nesbitt et al. 2017 recovered and quite similar to the large reptile tree (LRT, 1560 taxa). Here the key was not ‘taxon inclusion’ or the number of characters, but scoring and re-scoring more accurately. The .nex file is available now by request at info@reptileevolution.com.

I hope that young Sterling Nesbitt (2011)
was not unduly influenced or misguided in his scoring (or lack of scoring) decisions in order to please his mentors. Over the past eight years the LRT has been derided and suppressed because it differs from the traditional paradigm promoted by Nesbitt and others. When taxa, like Diandongosuchus and Chilesaurus, are tested without prior restraints, then they, too, nested as they did earlier in the LRT (and without citation). Details here and here.

Figure 1. Reduced and rescored cladogram from Nesbitt et al. 2017. This cladogram now greatly resembles the LRT.

Figure 1. Reduced and rescored cladogram from Nesbitt et al. 2017. This cladogram now greatly resembles the LRT.

The cladogram of Nesbitt  et al. 2017
did not hold up to experimentation and testing. It followed Nesbitt 2011, which followed the paradigm of the day: that rauisuchians gave rise to crocodilians within a then popular clade, Pseudosuchia, based on ankle traits, for the last several years invalidated by the results of the LRT.

Along the way,
I learned more about OrthosuchusKayentasuchus and Yonghesuchus (which now nests closer to Saltopus), which lacks a skull. Two of these taxa are not in the LRT, but soon will be.

Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Nesbitt S et al. 2017. The anatomy of Teleocrater Rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic). Journal of Vertebrate Paleontology 142-177. https://doi.org/10.1080/02724634.2017.1396539

2 thoughts on “Digging into another cladogram, pt. 7 (finished!)

  1. I wrestled with whether to respond to this. I’ve decided to do so – I don’t know if you’ll learn from it, but maybe others will.

    You owe Sterling Nesbitt a public apology. Your comments here are inaccurate, borderline libelous, and offensive.

    In particular, your allegation that he might have manipulated his data to avoid angering his mentors crosses a line. His results actually did challenge standing consensus at the time. His was the first analysis to suggest phytosaurs aren’t crown-group archosaurs, for example. The mere suggestion – even with qualifications – that Sterling might have acted dishonestly is a personal insult that calls for an apology from you.

    Sterling’s codings were based on first-hand observation of specimens. I’ve seen many of the same specimens. His codings are accurate. If he didn’t code something, it’s either because he didn’t have access to the material (and acted in a scientifically appropriate way) or didn’t think preservation was sufficient to allow assessment. These are simple facts.

    I know you don’t agree, but every single professional who’s ever worked with specimens knows photographs are a very poor substitute for the original material. This isn’t some sort of orthodoxy we’re fighting to uphold – it’s an observation borne of extensive experience. I’ve worked with crocodyliforms for close to 30 years. I’ve added species based on photos and/or published descriptions in the past – nearly always reluctantly and only because the species in question has critical biogeographic or stratigraphic implications. The total number such species I didn’t have to completely recode when I finally saw the actual specimens is precisely zero. It’s never happened.

    Hopefully, your apology will be presented here. You slandered Sterling publicly, and so your apology should be equally public. If not, please let us know when you’ve offered it to him privately.

    • No apology is necessary. No slander was committed. I’ll say it again, my fervent hope is that no student bows down to paradigm, tradition and the pressures of serving a mentor.

      Not sure why you are choosing this moment in time to defend Nesbitt’s work. His work has been strongly criticized here for the last eight years due to untenable results.

      You wrote: “His was the first analysis to suggest phytosaurs aren’t crown-group archosaurs, for example.”

      I noted Nov 26, 2011 that Nesbitt 2007 nested Parasuchia between Stagonolepidae and Pterosauria. Later, Nesbitt 2011 nested phytosaurs derived from Euparkeria and basal to two clades within the Archosauria. Ornithosuchidae was at the base of one branch and pterosaurs were at the base of the other. None of these nestings demonstrate a gradual accumulation of traits. I thought it was all due to taxon exclusion. The latest dive into the missing and miscoded traits of Nesbitt et al. revealed more issues. These resulted in a cladogram that, like the 2007 and 2011 studies, did not provide a microevolutionary documentation of increasingly derived traits, which is something the LRT does very well.

      You professionals need to clean your own house, and not wait for an outsider to do it for you.

      While we’re on that note, the crown-group archosaurs include only crocs and dinos when pertinent taxa are included and irrelevant taxa are excluded. If you don’t get those results, you might have to add to and prune your own taxon list, trusting that all traits are scored correctly.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.