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.
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.
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 firstname.lastname@example.org.
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.
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.
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