Gracilisuchus revisited and tweaked

Revised October 30, 2019 and November 4, 2019
as I revise the holotype specimen by deleting the limbs. The nesting does not change.

The basal bipedal crocodylomorph,
Gracilisuchus (Figs. 1-3), was one of the first taxa in the large reptile tree (LRT, 1592 taxa), back when there were about 260? taxa. At the time I used Romer’s 1972 reconstruction (Fig. 5) to score data points. That turned out to be a freshman mistake. Romer filled in the missing taxa with the so-called Tucuman specimen, PVL4597, but kept the hind limbs and feet from the holotype slab. The hips and tail are not preserved in the holotype specimen PULR8 (Fig. 1).

Figure 1. Gracilisuchus revised with new, slightly longer legs  and more precise feet after tracing the holotype. Romer added a pelvis and tail that are erased here.

Figure 1.  Gracilisuchus revised with the subtraction of limbs and tail.  Romer added limbs and a tail that are erased here.

 

 

A larger cladogram problem.
Lecuona, Desojo and Pol 2017 report, “The phylogenetic relationships of G. stipanicicorum were evaluated based on an extensive phylogenetic analysis of Archosauriformes expanding a previous dataset (Nesbitt, 2011) in terms of both taxon and character sampling.”  As we learned earlier in a 7-part series, the analysis by Nesbitt 2011 and all those that followed are flawed throughout. Those analyses include unrelated taxa and exclude pertinent taxa. When scores are corrected or filled in where appropriate the resulting topology closely matches the LRT.

Here’s a good idea:
Don’t trust ANY previously published cladograms. Build your own.

This revision gave me an opportunity to update the text
on the Gracilisuchus page. That was needed due to the large number of additional taxa added near Gracilisuchus over the last 8-9 years. With the loss of limbs data, the current nestings of Gracilisuchus and a headless taxon wrongly attributed (Lecuona and Desojo 2011) to Gracilisuchus, PVL4597, did not change with these corrections. Just goes to show, it’s the taxon list, not the character list, that is key to understanding hypothetical interrelationships.

Basal Crocodylomorpha

Figure 5. Basal Crocodylomorpha, including Gracilisuchus, Saltopus, Scleromochlus and Terrestrisuchus. That’s the old Gracilisuchus pictured here, with tail and hips.

Thanks to
reader Neil P for bringing Gracilisuchus back to my attention.


References
Butler RJ, Sullivan C, Ezcurra MD, Liu J, Lecuona A and Sookias RB 2014. New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and
the biogeography of the archosaur radiation. BMC Evolutionary Biology 14:1-16.
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Lecuona A, Desojo JB and Pol D 2017. New information on the postcranial skeleton of Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position. Zoological Journal of the Linnean Society XX:1–40.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.

wiki/Gracilisuchus

2 thoughts on “Gracilisuchus revisited and tweaked

  1. Dave, I’ve tried to tell you multiple times that the leg you are using to score Gracilisuchus (your figure 2) is part of Romer’s holotype of Lagosuchus, not a referred Lagosuchus specimen. Lecuona et al. had nothing to do with it, apart from acknowledging it in their figures. Lagosuchus is based on that leg (that is the purpose of a holotype, after all), so arguing that the leg belongs to Gracilisuchus is equivalent to synonymizing the two taxa, which we can both agree is an absurd proposal.

    If I can properly convince you that it is unscientific to merge the holotypes of these two taxa, hopefully then you would understand that there are no hindlimb remains in Gracilisuchus specimens apart from PVL-4597. Based on my understanding of your scores, supposed hindlimb differences are the only factors which you use to refute our argument that PVL-4597 is a Gracilisuchus specimen. But these differences cannot be proven to exist, because there are no other Gracilisuchus hindlimb specimens. Your referral of the Lagosuchus holotype to Gracilisuchus is a mistake perpetuated by ignorance of the history of these taxa. Romer knew the leg didn’t belong to Gracilisuchus before Gracilisuchus was even named. If this fundamental point has not been properly communicated to you, we need to chat until you understand what I’m trying to tell you.

    • You are correct. The hind limb on the other side of the slab is connected to another set of vertebrae as I see by reviewing the literature on Lagosuchus. My mistake, now corrected. As much as possible I try to avoid chimaera taxa and so continue to score the holotype of Gracilisuchus (now sans arms and legs) apart from PVL-4597. They continue to nest apart. Gracilisuchus continues to set with the MCZ 4116 specimen. PVL 4597 continues to nest between Turfanosuchus and Archosauria in the LRT.

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