Stockdale and Benton 2021 explain why to avoid super trees and super matrices

…then Nature publishes their supertree/supermatrix
analysis of crocodilians and their ancestors using 175 source trees published since 2010.

Unfortunately
Stockdale and Benton presented their charts and graphs without a valid phylogenetic context due to massive outgroup taxon exclusion. Their in-group appears to be okay.

Stockdale and Benton report, 
“There is no published phylogenetic hypothesis that encompasses all Pseudosuchia, as well as molecular data from living taxa. Therefore, we estimated a new phylogenetic hypothesis for this study.”

Molecular studies rarely, if ever, replicate trait-based studies. It’s no exaggeration to report that everyone know this. So, why even waste time with molecular studies when dealing with deep time taxa?

“A matrix based approach was also ruled out, because collecting character data for such a large matrix from the literature and vetting characters for redundancy would have been impractical.”

Here’s a suggestion: Add all the taxa from the various source cladograms to one study and use only the characters from that one study until resolution starts to falter.

Or start with fewer taxa and fewer characters (about 200 each) to establish the tree topology. Then add more taxa. I can tell you from experience, this works.

“In addition, such a large matrix would have introduced a significant fraction of missing data, which could undermine the quality of a finished tree.”

Here’s a suggestion: employ relatively complete taxa to figure out the tree topology. Then add less complete taxa until resolution starts to falter.

“The phylogenetic hypothesis used in this study is based on a formal supertree analysis. Formal supertrees use a systematic approach to assimilating multiple smaller topologies into a single tree. Liberal formal supertree methods enable a well-resolved consensus topology to be estimated from source trees that are incongruent.”

Both supertree methods enable workers to trust prior studies, rather than examining specimens, photos and engravings. That’s antithetical to standards established by paleontologists for the rest of us.

“The supertree was estimated from a sample of 175 source trees published since 2010, each re-analysed from their original source matrices using Bayesian inference and the MK model. The supertree was dated using the equal method; the dated supertree contained a total of 579 archosauromorph taxa, including 24 extant species.”

And yet, despite their large taxon list, Stockdale and Benton managed to exclude a long list of outgroup taxa found to be pertinent by the LRT (subset Fig. 1), Missing taxa include many basal crocodylomorphs and outgroup poposaurs. Stockdale and Benton also omitted members of the only other clade in the Archosauria (by definition, as recovered in the LRT): Dinosauria. In other words, Herrerasaurus and Junggarsuchus should have been included. And where was Benton’s Scleromochlus?

“This tree was then trimmed to match the 280 pseudosuchian taxa included in the body size data. This phylogenetic approach was implemented to eliminate as many sources of error as possible.”

Trimmed? Sounds subjective. Don’t gloss over this point.

Source errors? The whole idea of using a super tree analysis is to avoid looking at taxa, photos of taxa or the literature. Why not at least peek at the taxa to double-check for possible source errors?

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure 1. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha. Fewer derived crocs here, but a wider gamut of outgroup taxa validate the LRT.

Stockdale and Benton (SuppData) report on
the “limitations of informal super trees”

“All supertrees, informal or otherwise, share a common drawback that they are dependent on the accuracy of the source trees from which they are estimated. This is especially true of informal trees where topology is copied from older publications, where the data or methodology may be outdated. Informal supertrees are also entirely subjective, and by definition bias analyses in favour of the author’s own views.”

True. So why didn’t Stockdale and Benton listen to themselves? Why did referees and editors permit this to be published?

Add taxa and the traditional clade ‘Pseudosuchia’ becomes invalid, polyphyletic.

“If there is controversy about the evolutionary relationships within a clade, the number of possible informal supertree topologies may become excessive.”

No. This is professional baloney. There is only one tree and it models actual evolutionary events. It’s our job to recover that one tree (subset Fig. 1).

“For example, the positions of several member clades within the Pseudosuchia differ between analyses. The Thalattosuchia have been resolved as a derived clade within the Neosuchia, a basal sister clade to the Crocodyliformes, or an intermediate clade within the Mesoeucrocodylia but outside the Neosuchia.” 

That means someone or several someones made a mistake. Fix the mistakes. See the Stockdale and Benton 2016 text for other examples they cite.

“It would be difficult to draw meaningful conclusions from so many trees if they are considered equally likely; it is therefore necessary to develop a consensus of these different viewpoints based on the strongest evidence.”

More subjective professional baloney. Consensus of viewpoints? How about just taking a quick peek at some specimens, photos of specimens or even drawings of specimens.

“Supermatrix approaches avoid many of the subjectivity issues associated with informal supertrees. Supermatrices lack a specific technical definition, however the term is broadly used to describe phylogenetic analysis of a single, comprehensive matrix. A supermatrix of the Pseudosuchia would require in excess of 500 taxa. Estimating such a large phylogenetic tree from a single matrix represents a formidable challenge, either in the sheer number of fossils to be examined and their characters scored, or by the integration of existing matrices.”

Quit whining! Do the work. The LRT passed 500 total taxa eight years ago and now includes 3-4x that number (including pterosaurs and therapsid skulls).

Here’s a suggestion: Start with 150 to 200 taxa. That will get you will started with a rough estimate of the final tree topology. Later adding taxa one or two at a time will slowly fill in the gaps and solidify the tree topology.

If two taxa are nearly identical in every detail, they are probably related. Drop one. Pick it up later if you really need to.

First attend to the basic problems. The Stockdale and Benton study has basic issues based on taxon exclusion among outgroup taxa. The ingroup taxon list appears to be just fine.

“Very large morphological character matrices present a significant problem in the accumulation of inapplicable characters.For example, a matrix of crocodile-line archosaurs would likely contain characters relating to the morphology of osteoderms, despite osteoderms being absent in some members.”

That’s no problem for the LRT. For example, the score ‘absent’ is available where appropriate. Consider this paper an example and cautionary tale showing how to get published while whining about what not to do.

“Therefore, it is not reasonable to assume that the time invested in building a very large supermatrix will be rewarded with a high quality phylogenetic analysis.”

This statement was falsified by the LRT with over 2000 taxa. Just do the work. Show your work. Repair bad scores. Report results. If you don’t get one tree go back in there and figure out what went wrong. If a skull-only taxon nests with a skull-less taxon, eliminate one of them.

“Conservative approaches handle incongruences between source trees by presenting them as unresolved nodes in the final topology.”

If something is wrong, fix it. Do the work. Don’t let bad data infiltrate your matrix.

“The MRP method is an example of a liberal supertree approach, where incongruences between source trees are resolved democratically, with the better-supported topology being retained in the final supertree. The MRP method is a pragmatic choice, since it can be implemented using readily available software without consuming excessive computer processing power.”

If something is wrong, fix it. Do the work. Don’t let bad data infiltrate your matrix.

“Studies sceptical of supertrees, such as Gatesy et al., have concluded that these issues are insurmountable and that supertree methods should be avoided altogether.”

Just do the work. Don’t rely on, or trust the work of others.

“A rebuttal by Bininda-Emonds et al. concluded that these problems could be mitigated through careful source tree selection protocols and stated that supertrees are a necessity due to the inherent impracticality of super matrices.”

Stockdale and Benton don’t want to do the necessary work.

From the Stockdale and Benton Discussion Section:
“The supertree identifies the Phytosauria as a monophyletic group within Pseudosuchia, closer to extant crocodilians than to Avemetatarsalia.”

Adding missing taxa (as in the LRT) separates Phytosauria from all other included taxa. “Pseudosuchia” becomes an invalid polyphyletic clade when missing taxa are included. “Avemetatarsalia” is a junior synonym for the older clade Reptilia when missing taxa are included. Professor Benton is infamous for cherry-picking taxa. Better to let a wide gamut analysis tell you which taxa to include and exclude.

As described early in 2012,
adding pertinent taxa separate Pararchosauriformes (Proterosuchus is the last common ancestor) from the Euarchosauriformes (Euparkeria is the last common ancestor). Neither of these taxa are in the Stockdale and Benton taxon list. Their last common ancestor is Younginoides. The clade Archosauriformes begins there. The rest follow (Fig. 1).

Stockdale and Benton attempted to describe
environmental drivers of body size in crocs. Unfortunately, without a valid phylogenetic context, and omitting so many pertinent taxa, the rest of the information they so carefully prepared is hobbled by their own self-confessed lack of effort.

Don’t whine about doing the necessary work.
Get the broad basics right. The you’ll have that powerful cladogram for the rest of your career. Only then do the more focused work.


References
Bininda-Edmons ORP et al. (7 co-authors) 2003. Supertrees are a necessary not-so- evil: a comment on Gatesy et al. Syt. Bio. 52, 724-729. [not sure how this 2003 comment precedes the Gatesy et al. 2004 paper].
Gatesy J, Baker RH and Hayashi C 2004. Inconsistencies in arguments for the supertree approach: supermatrices versus supertrees of Crocodylia. Syt. Bio. 53:342-355.
Stockdale MT and Benton MJ 2021. Environmental drivers of body size evolution in crocodile-line archosaurs. Nature Communications Biolody 4:38 https://doi.org/10.1038/s42003-020-01561-5 

https://pterosaurheresies.wordpress.com/2012/01/13/introducing-the-pararchosauriformes/

Some news sources took the bait.
Since Scleromochlus and other basal bipedal crocs were not included, the headline in The Conversation is bogus. Here’s what The Conversation reported.

 

 

 

 

 

SVP abstracts 8: µCT studies on Scleromochlus reveal it is a ‘reptile’

Foffa et al. 2020 apply µCT scanning technology
to the tiny Late Triassic Scleromochlus (Fig. 1). This bipedal crocodylomoph with tiny fingers was Michael Benton’s (1999) and Chris Bennett’s (1996) cherry-picked choice to be the taxon closest to pterosaurs (whenever the actual sisters (Peters 2000) were omitted).

Faxinalipterus matched to Scleromochlus. The former is more primitive, like Gracilisuchus, in having shorter hind limbs and more robust fore limbs. The maxilla with fenestra and fossa, plus the teeth, are a good match.

Figure 1. Faxinalipterus matched to Scleromochlus. The former is more primitive, like Gracilisuchus, in having shorter hind limbs and more robust fore limbs. The maxilla with fenestra and fossa, plus the teeth, are a good match.

Scleromochlus has become more popular lately.
Earlier this year, Bennett 2020 provided new drawings, but not much new insight. His cladograms failed to recover a single node on which to nest Scleromochlus.

From the Foffa et al. 2020 abstract:
“The herpetofauna of the Lossiemouth Sandstone Formation (Late Triassic) of Elgin (Moray, Scotland) includes several close relatives of key groups such as dinosaurs, pterosaurs, crocodilians and lepidosaurs, although the affinities of some taxa within this assemblage are contentious.”

How contentious?

  • Pterosaurs? No.
  • Dinosaurs? No.
  • Crocodilians (= Crocodylomporha)? Yes: Saltopus and Scleromochlus.
  • Lepidosaurs? No, according to Wikipedia and the LRT.

Continuing from the Foffa et al. 2020 abstract:
“The specimens of this assemblage are notoriously challenging to study because of their preservation as voids in sandstone. Historically, the ‘Elgin reptiles’ have been studied primarily using physical molds, which only provide incomplete, and potentially distorted information – an issue that particularly affects small-bodied taxa. Here we use microcomputed tomographic (μCT) techniques as an alternative method to study these important specimens, and access hidden parts of their skeletons.”

“Scleromochlus taylori is one of the most controversial taxa within the assemblage. It is an enigmatic, small-bodied, bipedal reptile that was long hypothesised to be closely related to dinosaurs and pterosaurs, and is represented by several specimens of varying completeness.”

Not an enigma. In the large reptile tree (LRT, 1749+ taxa; subset Fig. 2), and earlier (Peters 2002) nested Scleromochlus as a basal bipedal crocodylomorph. Add pertinent sister taxa (and let’s see your reconstructions and tracings to make sure interpretations are correct) to confirm or refute.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 2. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Continuing from the Foffa et al. 2020 abstract:
“It was recently reinterpreted as a quadrupedal ‘hopper’, (Bennett 2020) positioned phylogenetically either within doswelliid archosauriforms, or outside of the Archosauria + Erythrosuchidae clade. Neither of these interpretations has been universally accepted, and other aspects of the biology of Scleromochlus are also contentious.

Taxon exclusion is the universal problem with prior studies. Given the proportions of Scleromochlus (Fig. 1) and the proportions of its phylogenetic sisters (Fig. 2), why force it into an awkward quadrupedal posture?

Figure 1. Taxa from the croc subset of the LRT to scale. Click to enlarge.

Figure 1. Taxa from the croc subset of the LRT to scale. Click to enlarge.

Continuing from the Foffa et al. 2020 abstract:
“Here we analyse the first μCT scan data collected for Scleromochlus, using all available specimens, and show that historic molding incompletely captured its anatomy. We access and describe previously inaccessible (and thus unaltered) portions of its skeleton including a complete
[unintentionally left blank], as well as new details of already described regions. Overall, we clarify previous ambiguous features such as vertebral count, dorsal rib length and curvature, and reveal new details from the neck, tail, girdles, fore and hindlimb (particularly manus, femur and pes). We use this information, alongside that from multiple generations of molds, to shed light on some of the most controversial aspects of its anatomy, phylogenetic relationships, taphonomy, and ecology.”

Well,  that’s a lot of teasing without telling readers what Scleromochlus is. The title of the abstract only refers to Scleromochlus as a ‘reptile/’. No other conclusions are presented.


References
Foffa D, Barrett P, Butler R, Nesbitt S, Walsh S, Brusatte S, Fraser N 2020. New Information on the Late Triassic reptile Scleromochlus taylori from µCT data. SVP abstracts 2020.

http://reptileevolution.com/scleromochlus.htm

Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.

wiki/Scleromochlus

 

Basal bipedal crocs reviewed, with a focus on Barberenasuchus

Leardi, Yáñezc and Pol 2020 bring us
their thoughts on new and previously discovered South American crocodylomorphs. In the large reptile tree (LRT, 1737+ taxa; subset Fig. x) only Crocodylomorpha + Dinosauria comprise the Archosauria. The Poposauria (= Turfanosuchus and kin;  Fig. 1) is the proximal outgroup.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

From the Leardi, Yáñezc and Pol Abstract
“Crocodylomorpha is a clade that has its origins during the Late Triassic and attained a global distribution early in their radiation.In this contribution we review the crocodylomorph Triassic record in South America by analyzing three units that have yielded fossils of the clade: the Santa María Supersequence in Brazil; and, the Ischigualasto and Los Colorados formations in Argentina.”

Good start!

Figure 3. Barberenasuchus to scale with sister taxa, Herrerasaurus, Eoraptor, Lewisuchus and Trialestes and Junggarsuchus, but without the autapomorphies of its sister Herrerasaurus. At present Barberenasuchus is the basalmost dinosaur. Note the difference in the nasal between the dinosaurs and protodinosaurs.

Figure 1. Barberenasuchus to scale with sister taxa, Herrerasaurus, Eoraptor, Lewisuchus and Trialestes and Junggarsuchus, but without the autapomorphies of its sister Herrerasaurus. At present Barberenasuchus is the basalmost dinosaur. Note the difference in the nasal between the dinosaurs and protodinosaurs.

Continuing from the abstract
“Our review does not support previous assignments of the taxon Barberenasuchus (Fig. 1) from the Santa María Supersequence as a non-crocodyliform crocodylomorph, as it displays traits that are absent in all known crocodylomorphs and are present in other earlier branching archosaurs.”

The LRT agrees, but what Barberenasuchus isn’t isn’t the same as what it is (Fig. 2). Adding taxa gradually and ultimately nests all taxa.

Figure 2. Subset of the LRT focusing on the Phytodinosauria.

Figure 2. Subset of the LRT focusing on the Phytodinosauria.

More specifically,
the LRT nests Barbarenasuchus with Eodromaeus (Fig. 3) within the base of the Phytodinosauria (Fig. 2). Only Buriolestes is more primitive in this plant-eating clade of the Dinosauria.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow. Note the relatively small head of this plant eater.

Continuing from the abstract
“The Los Colorados Formation has a diverse crocodylomorph record being represented by a non-crocodyliform crocodylomorph (Psedhesperosuchus [Fig 1]) and two crocodyliforms (Hemiprotosuchus and Coloradisuchus).”

We looked at these two yesterday.

In the LRT, the Triassic is a little too early
for crocodyliforms. Adding taxa moves Hemiprotosuchus to the base of the Aetosauria. Coloradisuchus nests among basal bipedal crocodylomorpha, as we learned earlier. These are indeed found in the Triassic.

Continuing from the abstract
“Here we present a putative new non-crocodyliform crocodylomorph taxon from Los Colorados Formation. When compared with other crocodylomorph bearing formations around Pangea, the Ischigualasto Formation bears similarities with the crocodylomorphs assemblages of North America due to the presence of early branching crocodylomorphs (Trialestes) including “large-bodied” taxa. The Los Colorados Formation reveals a transitional composition corresponding to Norian and Early Jurassic assemblages of Pangea, as it shares the presence of basal crocodyliforms (i.e., protosuchids) typical of Early Jurassic units (e.g., Upper Elliot) and basal non-crocodyliform crocodylomorphs, widely present in Norian assemblages.”

Still waiting for data on this unnamed taxon. Meanwhile, let’s get back to Barberenasuchus (Figs. 1, 2).

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

When you add taxa, as done in the LRT,
Barberenasuchus brasiliensis (Mattar 1987, Middle Triassic) nests as a basal phytodinosaur. Barberenasuchus has shorter teeth and a larger orbit that more primitive carnivorous taxa. The skull is more gracile and smaller in size, as in other basal phytodinosoaurs.

Traditionally, and according to Wikipedia
“Barberenasuchus is an extinct genus of an archosauriform. Its phylogenetic position within Archosauriformes is uncertain; the author of its description classified it as a sphenosuchid crocodylomorph, while Kischlat (2000) considered it to be a rauisuchian. Irmis, Nesbitt and Sues (2013) stated that they “could not find any crocodylomorph character states preserved in the holotype specimen”.

Adding taxa makes the position of all taxa, including Barberenasuchus, in the LRT ever more certain.


References
Irmis RB, Nesbitt SJ and Sues H-D 2013.Early Crocodylomorpha. In Nesbitt SJ. Desojo JB and Irmis RB (eds.). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. The Geological Society of London. pp. 275–302. doi:10.1144/SP379.24
Kischlat E-E 2000.
 Tecodôncios: a aurora dos arcossáurios no Triássico. In Holz, M.; De Ros, L.F. (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS. pp. 273–316.
Leardi JM, Yáñezc I and Pol  D 2020. South American Crocodylomorphs (Archosauria; Crocodylomorpha): A review of the early fossil record in the continent and its relevance on understanding the origins of the clade. Journal of South American Earth Sciences. https://doi.org/10.1016/j.jsames.2020.102780
Mattar LCB 1987. Descrição osteólogica do crânio e segunda vértebrata cervical de Barberenasuchus brasiliensis Mattar, 1987 (Reptilia, Thecodontia) do Mesotriássico do Rio Grande do Sul, Brasil. Anais, Academia Brasileira de Ciências, 61: 319–333.

wiki/Eodromaeus
wiki/Barberenasuchus

Restoring the little crocodylomorph, Coloradisuchus

In 2017 Martinez, Alcober and Pol introduced a new
small (6cm skull length) crocodylomorph, Coloradisuchus abelini (Figs. 1, 2). The specimen is only known from the bottom half of its small skull + mandibles (Fig. 1). Unique for such a small Late Triassic croc, the nares are confluent at the snout tip, facing anteriorly. The premaxilla/maxilla suture is marked by a large oval fenestra exposing the lower canine in lateral view. This trait is typically found in protosuchids (Fig. 5), but also to a lesser extent in Gracilisuchus (Fig. 3) and Dibothrosuchus (Fig. 2).

Figure 1. Coloradisuchus skull from Martinez, Alcover and Pol 2017. Colors added.

Figure 1. Coloradisuchus skull from Martinez, Alcover and Pol 2017. Colors added. Skull length 6 cm. Restoration according to Dibothrosuchus.

The question is:
where to nest Coloradisuchus?

Figure 2. Dibothrosuchus compared to scale with the much smaller Coloradisuchus.

Figure 2. Early Jurassic Dibothrosuchus compared to scale with the much smaller Triassic Coloradisuchus.

From the abstract:
“Protosuchids are known from the Late Triassic to the Early Cretaceous and form a basal clade of Crocodyliformes. We report here a new protosuchid crocodyliform, Coloradisuchus abelini, gen. et sp. nov., from the middle Norian Los Colorados Formation, La Rioja, northwestern Argentina. Our phylogenetic analysis recovers Coloradisuchus abelini within Protosuchidae, as the sister group of the clade formed by Hemiprotosuchus and two species of Protosuchus (P. richardsoni and P. haughtoni). The new protosuchid C. abelini increases the diversity of crocodyliforms in the Late Triassic and, together with H. leali from the same stratigraphic levels of the Los Colorados Formation, shows that the diversification of basal crocodyliforms was probably faster and/or older than thought previously.”

It is easy to see why the authors assumed Coloradisuchus was a protosuchid, but adding convergent taxa moves it away. On the other hand, distinctly different Hemiprotosuchus (Fig. 4) clearly nests elsewhere.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 3. Gracilisuchus skull updated with new colors. Skull length = 8cm.

Here in the LRT
Hemiprotosuchus nested far from protosuchids, at the base of the Aetosauria (Fig. 4). Protosuchids are terminal taxa also arising form small bipedal ancestors.

Figure 3. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Figure 4. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Adding Coloradisuchus
to the large reptile tree (LRT, 1737+ taxa) nests it between the much larger Early Jurassic Dibothrosuchus (Fig. 2) and the similarly-sized Middle Triassic Gracilisuchus (Fig. 3). These taxa also share a fenestra between the naris and antorbital fenestra, though much narrower than in protosuchids and Coloradisuchus. Martinez, Alcober and Pol did not test Dibothrosuchus and Gracilisuchus in their abbreviated cladogram consisting only of protosuchids and putative protosuchids.

Figure 2. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Figure 5. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Martinez, Alcobar and Pol note:
“The only known Triassic record of Protosuchidae is Hemiprotosuchus leali, from the upper levels of the middle Norian Los Colorados Formation (Bonaparte, 1971; Kent et al., 2014), and a putative, unnamed protosuchid from thelate Norian–Rhaetian Quebrada del Barro Formation (Martınez et al., 2015), both from northwestern Argentina.” 

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

With Hemiprotosuchus now nesting with coeval aetosaurs,
Coloradisuchus in the Triassic nests temporally and phylogenetically apart from other protosuchids. Unfortunately, due to preservation issues (Fig.1), relatively few traits can be scored for Coloradisuchus. Even so, moving Coloradisuchus to the protosuchid lineage adds five steps. That may change with further study or better data. Let’s keep working on this one.


References
Martinez RN, Alcober OA and Pol D 2017. A new protosuchid crocodyliform (Pseudosuchia, Crocodylomorpha) from the Norian Los Colorados Formation, northwestern Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1491047.

 

Gracilisuchus 2020: Two new specimens added to the genus

Lucuona, Desojo and Cerda 2020 bring us new information
on Gracilisuchus (Figs. 1, 3), a basal bipedal crocodylomorph in the large reptile tree (LRT, 1734+ taxa; subset Fig. 2). Gracilisuchus was originally considered an ornithosuchid by Romer (1972). Others considered it to nest between Parasuchus and Stagonolepis (Benton and Clark 1988), as the sister to Postosuchus (Juul 1994) or as a sister to Postosuchus and Erpetosuchus (Benton and Walker 2002). All suffered from taxon exclusion.

Figure 4. The PVL 4597 specimen nests at the base of the Archosauria, not with Gracilisuchus.

Figure 1. The PVL 4597 specimen (above)  nests at the base of the Archosauria, not with Gracilisuchus (below). Gracilisuchus based on holotype  PULSR8 with the skull diagram (MCZ4117)  based on Romer 1971. See figure 3 for an update on that skull.

Gracilisuchus stipanicicorum
(Romer 1972; Butler et al. 2014; Ladinian, Middle Triassic, ~230 mya, 30 cm long; holotype PULSR8) is a basal crocodilomorph. In the LRT Gracilisuchus was derived from a sister to Dibothrosuchus (Fig. 5), and preceded both Saltopus and Scleromochlus in the LRT. These three taxa are not mentioned in the Lucuona et al. text.

Taxon exclusion
is the major and continuing problem in vertebrate paleontology. The LRT is trying to repair that problem simply by adding taxa.

From the Lucuona et al. 2020 abstract:
“Gracilisuchus stipanicicorum Romer, 1972 is a basal suchian from the Late Triassic Chañares Formation (Argentina), nested in the recently erected Gracilisuchidae, along with Turfanosuchus dabanensis Young, 1973 and Yonghesuchus sangbiensis Wu et al., 2001 from China.”

Adding taxa separates these three genera in the LRT (subset Fig. 2) and invalidates any clade with only these three polyphyletic members. These three taxa and all their descendants do form an unnamed clade: Poposauria + Archosauria in the LRT, which was not their intention, nor that of Butler et al. 2014, who erected the clade with these three members with the same criticism about 5 years ago.

Figure 2. Subset of the LRT focusing on Crocodylomorpha. Matching Nesbitt et al. 2005, the LRT nests Redondavenator near the base of the Crocodylomorpha.

Figure 2. Subset of the LRT focusing on Crocodylomorpha. Matching Nesbitt et al. 2005, the LRT nests Redondavenator near the base of the Crocodylomorpha.

Continuing from the abstract:
“The six known specimens of Gracilisuchus Romer, 1972 preserve most of the skeleton, lacking only most of the shoulder girdle and forelimb. Our latest fieldwork has recovered two specimens that preserve previously unknown elements, including the humerus, radius, and ulna, as well as the femur, presacral vertebrae, and paramedian osteoderms.”

By contrast the LRT (Subset Fig. 2) separates the PVL 4597 specimen from the PULSR8 holotype. The former nests at the base of the Archosauria (Crocodylomorpha + Dinosauria) at least two nodes away at present.

By combining two or more specimens
Lecuona et al. 2020 created an unwanted and confusing chimaera. A better practice is to score each specimen individually and let those that nest together do so. THEN create a chimaera if warranted.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 3. Gracilisuchus skull (MCZ 4117) updated. Note the slender fenestra between the premaxilla and maxilla, as in Dibothrosuchus.

The traditional short-faced Gracilisuchus specimen
MCZ 4116 (Fig. 4), was not mentioned in the Lecuona et al. 2020 text. Perhaps that’s a good thing since earlier the LRT nested the short-faced specimen with Trialestes.

Figure 1. The former Gracilisuchus specimens MCZ4116 and MCZ4118 with colors added.

Figure 4. The former Gracilisuchus specimens MCZ4116 and MCZ4118 with colors added.

Lecuona et al. consider Gracilisuchus to be a member
of the invalid clade, ‘Pseudosuchia’.

Bone histology studies
were performed on the two new specimens:

  1. CRILAR PV 480, “one and a half incomplete cervical centra articulated with each other and with two incomplete ribs, a series of three incomplete vertebrae articulated with one rib, dorsally in contact with the left row of the paramedian osteoderms, and posteriorly four ribs with no articulating vertebrae but in anatomical position (Fig. 2A, B), a series of six incomplete cervicodorsal vertebrae with some of their ribs preserved and half of a centrum attached posteriorly (Fig. 2C, D), and moulds of two short fragments of paramedian osteoderms”
  2. CRILAR PV 490, “two articulated cervical vertebra in contact with a short paramedian osteoderm series, one isolated dorsal vertebrae, left humerus, right ulna, right radius, left femur, and six histological sections of the femoral diaphysis and osteoderms”

Until phylogenetic analysis is performed on each specimen,
we can’t be sure that these are indeed Gracilisuchus specimens.

Figure 2. Images from Wu et al. 1993, colors and hind limbs added. Compare to skull in figure 1.

Figure 5. Images from Wu et al. 1993, colors and hind limbs added. Compare to skull in figure 1.

Until Lucuona et al. 2020 add pertinent taxa 
they will not understand the phylogenetic context of the holotype specimen, the referred specimens and all pertinent, but unrelated taxa. That means whatever they have to say about the new fossils has to be considered with some reservation. They think all this material belongs to Gracilisuchus. The LRT demonstrates at least one specimen nests apart from the holotype. Better to know with validation, than to guess.


References
Benton MJ and Clark JM 1988. Archosaur phylogeny and the relationships of the Crocodilia in MJ Benton (ed.), The Phylogeny and Classification of the Tetrapods 1: 295-338. Oxford, The Systematics Association.
Brinkman D 1981. The origin of the crocodiloid tarsi and the interrelationships of thecodontian archosaurs. Breviora 464: 1–23.
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.
Juul L 1994. The phylogeny of basal archosaurs. Palaeontographica africana 1994: 1-38.
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.
Lecuona A, Desojo JB and Cerda IA 2020. New information on the anatomy and histology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia) from the Chañares Formation (early Carnian), Argentina. Comptes Rendus Palevol 19 (3): 40-62. https://doi.org/10.5852/cr-palevol2020v19a3
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. Journal of Vertebrate Paleontology 13(3):287-308.
Romer AS 1971. The Chañares(Argentina) Triassic reptile fauna. Two new bu incompletely known long-limbed pseudosuchians. Breviora 378:1–10.
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

Redondavenator enters the LRT, then exits

Several taxa tested
in the large reptile tree (LRT, 1710+ taxa; subset Fig. 2) do not remain in the LRT or the MacClade file forever. Typically they are known from very few parts, like a single jawbone. These bits and pieces enter the LRT to see where they nest, and then they exit.

In this case,
Redondavenator quayensis (Nesbitt et al. 2005; Fig. 1; NMMNH P-25615) is known from a partial snout, a partial coracoid and a partial scapula.

Figure 1. Redondavenator snout from Nesbitt et al. 2005 and colored here.

Figure 1. Redondavenator (NMMNH P-25615) snout from Nesbitt et al. 2005 and colored here.

According to the abstract
“Its exact phylogenetic position [within Crocodylomorpha] could not be determined from the preserved material, but key characters suggest a phylogenetic position near the base of Sphenosuchia.”

According to the Systematic Position section:
“Redondavenator displays the following two sphenosuchian characters: reduced external naris and nasal is not bifurcated (no descending process).

According to the Palecology section:
“the complete skull of Redondavenator is estimated to be at least 60 cm long.”  That’s six to eight times larger than in sister taxa. “Anterior sculpturing [of the snout elements] has been correlated with semi-aquatic habits as an osteological correlate of dome pressure receptors that sense motion and help orientate the animal in water.” And that may explain the size difference.

Figure 2. Subset of the LRT focusing on Crocodylomorpha. Matching Nesbitt et al. 2005, the LRT nests Redondavenator near the base of the Crocodylomorpha.

Figure 2. Subset of the LRT focusing on Crocodylomorpha. Matching Nesbitt et al. 2005, the LRT nests Redondavenator near the base of the Crocodylomorpha, but several nodes away from Sphenosuchia.

According to Wikipedia,
Sphenosuchia include Sphenosuchus, Hesperosuchus, Dibothrosuchus and the CM 73372 specimen, which does not nest in the Crocodylomorpha in the LRT, but in the Rauisuchia alongside Smok and Teratosaurus.

Figure 2. Images from Wu et al. 1993, colors and hind limbs added. Compare to skull in figure 1.

Figure 2. Images from Wu et al. 1993, colors and hind limbs added. Compare to skull in figure 1.

The Wikipedia page on Sphenosuchia does not include
several of the taxa recovered here at the base of the Crocodylomorpha, including  Pseudhesperosuchus and Lewisuchus, taxa that nest on either side of Redondavenator here (Fig. 2). Redondavenator nests close to Dibothrosuchus, but lacks the accessory fenestra between the premaxilla and maxilla, as noted by Nesbitt et al. 2005.

Figure 5. Skull of Pseudhesperosuchus, a basal bipedal crocodylomorph close to Carnufex.

Figure 5. Skull of Pseudhesperosuchus, a basal bipedal crocodylomorph close to Carnufex.

It is important to know where taxa nest,
but if a snout specimen nests close to a post-crania specimen in the LRT, then loss of resolution will result. That is why Redondavenator will not remain within the MacClade file or the LRT. Testing has already indicated its correct node and that node agrees with the original nesting.

Thanks to Dr. Lucas for sending a PDF.


References
Nesbitt SJ, Irmis RB, Lucas SG and Hunt AP 2005. A giant crocodylomorph from the Upper Triassic of New Mexico. – Paläontologische Zeitschrift 79(4): 471–478, 4 figs., Stuttgart, 31. 12. 2005.

wiki/Redondavenator

Osteology of Carnufex 2015, 2016

Drymala and Zanno 2016 returned to their description of Carnufex,
(Fig. 1) a partial disarticulated basal crocodylomorph they published on a year earlier (Zanno, Drymala, Nesbitt and Schneider 2015; Fig. 2).

Figure 2. Data from Drymala and Zanno 2016 below. Elements colorized and moved around here above. It's always better NOT to use freehand illustrations.

Figure 1. Below: Data from Drymala and Zanno 2016. Above: Elements colorized and reconstructed  here. I prefer moving elements around to freehand illustration. The size of the lacrimal changes from the earlier paper (see figure 2).

There is also a strange data problem here. 
The 2015 paper included a reconstruction (Fig. 2) with a smaller lacrimal. The 2016 paper includes data and a reconstruction (Fig. 1) with a larger lacrimal.

Figure 3. Carnufex is basically a giant Pseudhesperosuchus. Here they are compared to one another to scale and with skulls side by side. Dark gray areas are imagined on the original at bottom by Zanno et al. Click to enlarge. With a skull 4x larger than that of Pseudhesperosuchus, Carnufex was a likely 4.4 meter long bipedal killer. Note the smaller orbit and deeper jugal. Both neural arches are missing a centrum.

Figure 2. Carnufex (from 2015 data) compared to Pseudhesperosuchus. Dark gray areas are imagined on the original at bottom by Zanno et al 2015. Compare to 2016 data in figure 1.

Unfortunately
their 2016 cladogram (Fig. 3) omitted several taxa key to understanding Carnufex and the clade Crocodylomorpha in the large reptile tree (LRT, 1697+ taxa; subset Fig. 4). For instance, in the LRT only Dinosauromorpha + Crocodylomorpha combine to form the clade Archosauria. So one wonders why no basal dinosaurs appear in the 2016 cladogram. Worse yet, a large number of basal bipedal crocodylomorphs are absent (list below in red at left).

Figure 1. Carnufex cladogram by Drymala and Zanno 2016. Color overlays added here.

Figure 3. Carnufex cladogram by Drymala and Zanno 2016. Color overlays added here. The phytosaur, Machaeoroprosopus does not belong in this list of euarchosauriformes. Turfanosuchus is a basal poposaur in the LRT. Gracilisuchus is a basal crocodylomorph in the LRT, so I suspect bad scores for those two taxa.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 4. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

After all the scoring changes
the prior nesting in the LRT of Carnufex with Pseudhesperosuchus (Fig. 5) remains the same, evidence that sometimes changes are not that important taxonomically.

Figure 5. Skull of Pseudhesperosuchus, a basal bipedal crocodylomorph close to Carnufex.

Figure 5. Skull of Pseudhesperosuchus, a basal bipedal crocodylomorph close to Carnufex.

In the LRT
dinosaurs are the closest outgroup to the basal bipedal crocs. In the LRT Pseudhesperosuchus is the closest taxon to Carnufex. Together these exclusions from the two Carnufex papers are errors of omission that change some hypothetical relationships.

If you’re going to use a comprehensive list of pertinent taxa,
it’s best to figure out first which taxa are the most pertinent. That’s the value of the LRT, where more taxa solve more problems here than more characters and fewer taxa do in smaller studies. You can always delete unrelated taxa once you have the proper phylogenetic context and wish to increase the focus of your study.


References
Drymala SM and Zanno LE 2016. Osteology of Carnufex carolinensis (Archosauria: Psuedosuchia) from the Pekin Formation of North Carolina and Its Implications for Early Crocodylomorph Evolution. PLoS ONE 11(6): e0157528. doi:10.1371/journal.pone.0157528
Zanno LE, Drymala S, Nesbitt SJ and Schneider VP 2015. Early Crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports 5:9276 DOI: 10.1038/srep09276.

wiki/Carnufex
wiki/Pseudhesperosuchus

Dibothrosuchus: a new ancestor for Gracilisuchus and Scleromochlus

According to Wikipediia,
Dibothrosuchus is a genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It is known from several partial skeletons and skulls. These fossils were found in Lower Jurassic rocks of YunnanChina.  Dibothrosuchus was a small terrestrial crocodylomorph.”

Here
in the updated crocodyomorph portion of the large reptile tree (LRT, 1658+ taxa; Fig. 6) Dibothrosuchus (Figs. 1, 2) nests among the most basal bipedal crocodylomorphs (phylogenetically far from Sphenosuchus (Fig. 7).

Figure 1. Dibothrosuchus skull fossil with colors added. Note the differences in this skull and the illustrated one in figure 2.

Figure 1. Dibothrosuchus skull fossil with colors added. Note the differences in this skull and the illustrated one in figure 2.

More specifically
an earlier sister to Late Jurassic Dibothrosuchus arose from a sister to Middle Jurrassic Junggarsuchus and Late Triassic Pseudhesperosuchus, (Fig. 3) and gave rise to smaller Middle Triassic Gracilisuchus (Fig. 4, 5), and Late Triassic Scleromochlus, Saltopus and Lagosuchus.

Figure 2. Images from Wu et al. 1993, colors and hind limbs added. Compare to skull in figure 1.

Figure 2. Images from Wu et al. 1993, colors and hind limbs added. Traditionally the postorbital is considered fused to the postfrontal. Compare to figure 1.

Dibothrosuchus elaphros (Early Jurassic, Simmons 1965; Wu and Chatterjee 1993) is known from an incomplete skeleton, lacking hind limbs and distal tail. In the LRT Dibothrosuchus nests at the base of bipeds AND was derived from bipeds, so phylogenetic bracketing indicates Dibothrosuchus was a biped, too.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Figure 3. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

As in descendant taxa,
the rostrum of Dibothrosuchus was perforated between the premaxilla and maxilla (Figs. 1, 2). The lateral temporal fenestra was elaborated with a quadrate that had three dorsal heads for a strong articulation with the skull roof. The cervicals and their ribs were quite robust. As in few other tetrapods, the cervicals and their ribs were deeper than the skull. The proximal carpals were longer than the metacarpals.

Figure 4. Present reconstruction of Gracilisuchus with skull based on Romer 1971. See figure 4 for an updated on that skull.

Figure 4. Present reconstruction of Gracilisuchus with skull based on Romer 1971. See figure 4 for an updated on that skull. Inset at upper right shows the broken femur (blue on the digram) and likely proximal carpals (green on the diagram).

Gracilisuchus stipanicicorum (Romer 1972; Butler et al. 2014; Ladinian, Middle Triassic, ~230 mya, 30 cm long; holotype PULSR8) is a basal crocodilomorph. It was derived from a sister to Dibothrosuchus and preceded both Saltopus and Scleromochlus.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 5. Gracilisuchus skull updated with new colors. Skull image from Butler et al. 2014. Note the tall fenestra separating the premaxilla from the maxilla, as in Dibothrosuchus (Fig. 2).

Gracilisuchus was originally considered
an ornithosuchid by Romer (1972). Others thought it nested between Parasuchus and Stagonolepis (Benton and Clark 1988), as the sister to Postosuchus (Juul 1994) or Postosuchus and Erpetosuchus (Benton and Walker 2002). Butler et al. (2014) nested Turfanosuchus, Gracilisuchus and Yonghesuchus together in a clade. Yonghesuchus is close (Fig. 5), but other omitted taxa are closer to the other two. Turfanosuchus is also close, but nests at the base of the Poposauria in the LRT (Fig. 6).

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 6. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

The Gracilisuchus hind limb paper by Leuona and Desojo (2011)
is about PVL 4597 (Fig. 7), a different genus, the last common ancestor of all archosaurs (crocs + dinos).

Figure 1. Taxa from the croc subset of the LRT to scale. Click to enlarge.

Figure 7. Taxa from the croc subset of the LRT to scale. Click to enlarge.

Lagosuchus talampayensis 
(Romer 1971) is a smaller specimen found on the same slab as the Gracilisuchus holotype. In the LRT Lagosuchus nests with Saltopus, both derived from a sister to Scleromochlus, which was derived from Gracilisuchus (Fig. 7)so all are members of the same tiny bipedal clade within Crocodylomorpha, all derived from a Middle to Early Triassic sister to Late Jurassic Dibothrosuchus.

This is an update
from blogpost #100 in October 2011 on basal bipedal crocs. Current blogpost # is something over 3000.


References
Benton MJ and Clark JM 1988. Archosaur phylogeny and the relationships of the Crocodilia in MJ Benton (ed.), The Phylogeny and Classification of the Tetrapods 1: 295-338. Oxford, The Systematics Association.
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.
Juul L 1994. The phylogeny of basal archosaurs. Palaeontographica africana 1994: 1-38.
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.
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. Journal of Vertebrate Paleontology 13(3):287-308.
Romer AS 1971. The Chañares(Argentina) Triassic reptile fauna. Two new bu incompletely known long-limbed pseudosuchians. Breviora 378:1–10.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Simmons DJ 1965. The non-therapsid reptiles of the Lufeng Basin, Yunnan, China. Fieldiana Geology. 15: 1–93.
Wu X-C and Chatterjee S 1993. Dibothrosuchus elaphros, a crocodylomorph form the Lower Jurassic of China and the phylogeny of the Sphenosuchia. Journal of Vertebrate Paleontology 13:58-89.

wiki/Gracilisuchus
wiki/Dibothrosuchus

Former Gracilisuchus specimens: now closer to Trialestes

Over the last several weeks
the large reptile tree (LRT, 1660+ taxa, subset Fig. 1) was updated once again with a focus on the Crocodylomorpha. Two congeneric taxa known from a few scraps were eliminated. More insightful identification of skull bones (Figs. 1, 5) settled old issues. Over the next several posts some of the newly recovered hypothetical interrelationships will be presented for review.

We’ll start here
with a new nesting in the LRT (subset Fig. 1) for the small specimens (MCZ4116 and MCZ4118, Fig. 2) formerly assigned to Gracilisuchus (Figs. 4, 5). Now they nest either as hatchling Trialestes (Fig. 3), or, just as likely, as phylogenetically miniaturized Middle Triassic predecessors to the much larger and highly derived Late Triassic basal crocodylomorph, Trialestes. In either case, now Trialestes and its tiny doppelgänger nest together in the LRT, closer to each other than either is to any other taxon, despite a magnitude or two difference in size (Fig. 3). Gracilisuchus nests several nodes away in the next clade (Fig. 1).

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades. Images changes every 5 seconds.

Hatchling? Trialestes? (MCZ 4116, MCZ 4118, originally Gracilisuchus, Brinkman 1981; Middle Triassic; Fig. 2). These two specimens have a taller, narrow skull than Gracilisuchus (Figs. 4, 5) and a long list of other distinct traits and proportions that nest them with the very much larger Trialestes (Fig. 3) in the LRT (Fig. 1).

Figure 1. The former Gracilisuchus specimens MCZ4116 and MCZ4118 with colors added.

Figure 2. The former Gracilisuchus specimens MCZ4116 and MCZ4118 (Middle Triassic) with colors added.

Trialestes romeri (Bonaparte 1982Triassolestes (Reig, 1963/Tillyard 1918) Carnian, Late Triassic ~235 mya) is known from scattered parts here reconstructed and restored (Fig. 3). Clark, Sues and Berman (2000) redescribed the known parts and admitted the possibility that this taxon combined dinosaurian and crocodylomorph characters.

Figure 2. Trialestes reconstructed. At upper left is MCZ4116 to scale.

Figure 3. Trialestes (Late Triassic)  reconstructed. At upper left is MCZ4116 to scale.

Quadrupedal Trialestes
is indeed different than most basal bipedal crocodylomorphs (see Pseudhesperosuchus), but it has elongate proximal carpals (Fig. 3) and a long list of other croc clade traits. The elongate ilium is typical of bipedal taxa indicating a bipedal ancestry. Additional sacrals that would have filled out the sacral set between the ilia (Fig. 3) are not known, but likely were present.

Figure 4. Present reconstruction of Gracilisuchus with skull based on Romer 1971. See figure 4 for an updated on that skull.

Figure 4. Present reconstruction of Gracilisuchus with skull based on Romer 1971. See figure 4 for an updated on that skull.

In Trialestes
the vertebral centra had excavated lateral surfaces, for bird-like air sacs. The radius was longer than the humerus, a character otherwise known only in dinosaurs. The long radiale was slightly shorter than the ulnare. The fingers were tiny, another indicator of a bipedal ancestry. The pelvis was semi-perforated with a well-developed supraacetabular crest, as in basal dinosaurs. The femoral head was inturned, indicating an erect posture. The ankle joint had a crocodile normal configuration and a functionally pentadactyl pes.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 5. Gracilisuchus (Middle Triassic) skull updated with new colors. Compare to figure 2.

The MCZ 4116 and MCZ 4118 specimens 
are coeval with Gracilisuchus in the Middle Triassic and similar in size, but share more traits in the LRT with highly derived Late Triassic Trialestes. As we’ve seen before, new morphologies often express their genesis in phylogenetically miniaturized taxa. That may be the case with the MCZ specimens, appearing millions of years before the much larger Trialestes. More discoveries, like an adult Trialestes in the Middle Triassic, will someday settle this ontogenetic and phylogenetic issue. This blogpost is where this issue starts. If this is not a novel hypothesis of interrelationships, let me know so I can promote the older citation.

Updates have been a continuing feature
of the LRT since its origin nine years ago, along with the steady addition of taxa to the present total of 1658 taxa, plus several hundred taxa in the pterosaur and therapsid cladograms. Correcting mistakes is standard practice in every science and every correction is another rewarding moment of discovery. Holding on to outdated and invalid hypotheses has been an acknowledged problem in paleontology.


References
Bonaparte JF 1982. Classification of the Thecodontia. Geobios Mem. Spec. 6, 99-112
Brinkman D 1981. The origin of the crocodiloid tarsi and the interrelationships of thecodontian archosaurs. Breviora 464: 1–23.
Clark JM, Sues H-D and Berman DS 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20(4):683-704.
deFranca MAG, Bittencourt JdS and Langer MC 2013. Reavaliação taxonomica de Barberenasuchus brasiliensis (Archosauriformes), Ladiniado do Rio Grande do Sul (Zona-Assembleia de Dinodontosaurus). Palaenotogia em Destaque Edição Especial Octubro 2013: 230.
Irmis RB, Nesbitt SJ and Sues H-D 2013. Early Crocodylomorpha. Pp. 275–302 in Nesbitt, Desojo and Irmis (eds). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. The Geological Society of London. doi:10.1144/SP379.24.
Kischlat EE 2000. Tecodôncios: a aurora dos arcossáurios no Triássico. Pp. 273–316 in Holz and De Ros (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS.
Lecuona A, Ezcurra MD and Irmis RB 2016. Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest-known crocodylomorphs. Papers in Palaeontology (advance online publication). DOI: 10.1002/spp2.1056
Reig, OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Riff D et al. 2012. Crocodilomorfos: a maior diversidade de répteis fósseis do Brasil. TERRÆ 9: 12-40, 2012.
Zanno LE, Drymala S, Nesbitt SJ and Schneider VP 2015. Early Crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports 5:9276 DOI: 10.1038/srep09276.

wiki/Trialestes

Revisiting Yonghesuchus: now a sister to Litargosuchus

Those two wide, low (flat) skulls should have been a dead-giveaway
linking Yonghesuchus (Fig. 1) to Litargosuchus (Fig. 2). One problem is: Yonghesuchus lacks skull roofing bones.

Figure 1. The skull of Yonghesuchus now compares well with that of Litargosuchus (figure 2).

Figure 1. The skull of Yonghesuchus now compares well with that of the slightly smaller Litargosuchus skull (figure 2).

Using phylogenetic bracketing
to restore large bulbous squamosals in Yonghesuchus, as in Litargosuchus, helps one realize the probable extent of loss of bone in this specimen, all other aspects being similar.

Figure 2. Litargosuchus with skull enlarged in 3 views. The Yonghesuchus skull is slightly larger than this one.

Figure 2. Litargosuchus with skull enlarged in 3 views. The Yonghesuchus skull is slightly larger than this one.

After a recent review of the Crocodylomorpha in the LRT,
several taxa, including Yonghesuchus, have moved around the cladogram. Some taxa were initially and naively nested several years ago and not looked at since. After the addition of dozens of taxa, new insights drive these changes. The difficulties are compounded by fossils with more cracks than sutures and other taphonomic jumbles.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 3. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Yonghesuchus sangbiensis (Wu, Liu and Li 2001) was the first tetrapod discovered from the Late Triassic of China. The presence of pterygoid teeth was thought to preclude membership within the Archosauria despite a suite of traits to the contrary. Here Yonghesuchus nests with flat-headed Litargosuchus within the Archosauria and within the Crocodylomorpha. The presence of pterygoid teeth is a reversal perhaps due to its very flattened skull and wide gape. The maxillary teeth were angled posteriorly. The antorbital fenestra was relatively large. The amphicoelus cervical vertebrae were elongated with ribs on elongated stems as in Dromicosuchus.

Litargosuchus leptorhynchus (Clark and Sues 2002; Late Triassicl; BP/1/5237) was a bipedal basal crocodylomorph from South Africa in the lineage of living crocs. It was derived from a sister to Terrestrisuchus and Erpetosuchus. Clark and Sues were unable to resolve their family tree, but they did not include three of the four above taxa

Butler et al. 2014 
suggested a sister group relationship between Gracilisuchus, Yonghesuchus and Turfanosuchus. In the LRT (Fig. 4) these three taxa are still not sisters. Several taxa intervene between every paired relationship suggested by these authors.

Figure 4. Terrestrisuchus nests basal to Yonghesuchus and Litargosuchus in the LRT.

Figure 4. Terrestrisuchus nests basal to Yonghesuchus and Litargosuchus in the LRT. This taxon displays the origin of the round squamosal. 

Speculation:
Like Litargosuchus, Yonghesuchus, was also a long-limbed, based on phylogenetic bracketing. Long-limbed quadrupedal Terrestrisuchus (Fig. 4) was a quadruped.


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.
Clark JM and Sues H-D 2002. 
Two new basal crocodylomorph archosaurs form the Lower Jurassic and the monophyly of the Sphenosuchia. Zoological Journal of the Linnean Society 136:77-95.
Wu X-C, Liu J and Li J-L 2001. The anatomy of the first archosauriform (Diapsida) from the terrestrial Upper Triassic of China. Vertebrata PalAsiatica39:251-265.

wiki/Litargosuchus
wiki/Yonghesuchus