Updated August 13, 2019
with a repair to a mistaken citation: Nesbitt et al. 2017, not Nesbitt and Desojo 2017.
A reader (NP) kindly supplied me with a cladogram
from Nesbitt et al. 2017 in regard to the placement of Revueltosaurus and Luperosuchus. This gave me a chance to reexamine scoring for some of the earliest taxa to enter the LRT and mistakes were found, but none to upset the tree topology.
The first step is to open the file.
I did this in MacClade, rather than Mesquite.
The next step is to omit all taxa outside the Archosauriforms
(as determined by the LRT), all taxa that are largely incomplete and all taxa absent from the LRT at present. 65 taxa remain to be tested along with 419 characters (almost twice as many as in the LRT).
Step 3 is to run the original data on PAUP.
This generates the tree topology (Fig. 1), based on a strict consensus of 260 trees. 373 traits are parsimony informative with regard to the shortened taxon list.
Step 4 is to order the 65 taxa in MacClade according to the PAUP results
because no tree file was saved by Nesbitt et al.
Step 5 is to give the results a cursory look.
- Many clades, like Dinosauria, Rauisuchia and Crocodylomorpha have similar memberships in the LRT and in Fig. 1, with notable exceptions.
- Arising from Euparkeria, the long-necked quadruped Yarasuchus gives rise to bipedal Scleromochlus and terminal Erpetosuchus. By contrast in the LRT Yarasuchus and the long-necked quadruped Qianosuchus are closely related.
- Members of the Crocodylomorpha in the LRT are split into 5 clades in Fig. 1.
- Members of the Poposauria in the LRT are split into 3 clades in Fig. 1.
- Members of the Ticinosuchus clade in the LRT are split into 3 closely related clades and one distantly related clade in Fig. 1.
- 373 traits were not enough to separate the members of the Ornithischia.
- Other issues I will postpone for the present.
The differences between the LRT and Nesbitt et al. 2017
are rather large. Why? We talked about Nesbitt 2011 in a 9-part series ending here.
With regard to Revueltosaurus,
Tasmaniosaurus and Fugusuchus are missing in Nesbitt et al. We looked at these three taxa earlier here. I will add them Nesbitt et al. to see what happens.
Desojo JB and Arcucci AB 2009. New material of Luperosuchus fractus (Archosauria: Crurotarsi) from the Middle Triassic of Argentina: the earliest known South American ‘Rauisuchian’. Journal of Vertebrate Paleontology 29(4): 1311-1315.
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
I’m happy that you’re finally making an effort towards this task, though I need some clarification on what file you’re using for the cladogram. I never sent you a nexus file from Nesbitt & Desojo (2017)’s Luperosuchus study, I only gave you a link to Nesbitt et al. (2018)’s Teleocrater study on morphobank, which doesn’t include Luperosuchus.
The topology you find after pruning is interesting. Pruning proterochampsians and phytosaurs seems to link ornithosuchids to aetosaurs and gracilisuchids to erpetosuchids, as well as shifting Yarasuchus stemward. I was able to replicate all of this in TNT, although having Yarasuchus at the base of Avemetatarsalia is equally parsimonious. Apparently without phytosaurs and proterochampsians to influence the ancestral state reconstruction, the topology of Pseudosuchia shifts around enough to connect certain clades which were always close, just not close enough. Ezcurra (2016) also had a stemward Yarasuchus (until Teleocrater was added in), as well as an erpetosuchid+ornithosuchid+aetosaur clade in a later revision after the addition of new Tarjadia data.
Thank you, Neil, for catching that wrong citation. As you might imagine, I’m struggling through this thing. Will report on a portion of it soon.