New paper, old Chanaresuchus: traditional taxon exclusion issues

A new look at the holotype of Chanaresuchus
by Trotteyn and Ezcurra 2020 provides crisp color photos of the holotype material from several angles, in white light and after µCT scanning.

Unfortunately their small focused cladogram
is a little too small and a little too focused for their taxon list. It might seem large because it includes 115 active taxa from a list of 151 total taxa from (Ezcurra 2016), but, as before, it omits several taxa that would move the thalattosaur, Vancleavea, and the pterosaur, Dimorphodon, out of Archosauromorpha (along with other lepidosaurs like Macrocnemus and Tanystropheus.

Earlier we looked at the many problems in Ezcurra 2016. The largest problem: Ezcurra did not and still does not understand that traditional diapsid taxa are diphyletic and convergent, with some among the Lepidosauria and others starting with Petrolacosaurus and kin within the Archosauromorpha. The Viséan last common ancestor of all reptiles is their last common ancestor.

Earlier we looked at a similar taxon list by Nesbitt 2011 in a 7-part series and demonstrated dozens of scoring errors. After corrections the tree topology came to match the large reptile tree (LRT, 1698+ taxa).

Figure 1. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa.

From the Trotteyn and Ezcurra 2020 abstract:
“Proterochampsids are one of the several diapsid groups that originated, flourished and became extinct during the Triassic Period. Here we redescribe, figure and compare in detail the holotype of one of these rhadinosuchine species, Chanaresuchus bonapartei from the Chañares Formation. Our new cladistic analyses find stronger support than previous studies for the monophyly of Rhadinosuchinae and the clades that include Doswelliidae + Proterochampsidae and Tropidosuchus + Rhadinosuchinae. Doswelliids are recovered within Proterochampsidae, as the sister taxon to the genus Proterochampsa, in some analyses under implied weights.”

If you find any taxa
in figures 1 and 2 missing from the above list (hint: there are several), those are the taxa Trotteyn and Ezcurra need to add to their next look at proterochampsids.

Figure 2. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

References
Ezcurra MD 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4, e1778. doi:10. 7717/peerj.1778
Trotteyn MJ and Ezcurra MD 2020. Redescription of the holotype of Chanaresuchus bonapartei Romer, 1971 (Archosauriformes: Proterochampsidae) from the Upper Triassic rocks of the Chañares Formation of north-western Argentina.
Journal of Systematic Palaeontology (advance online publication)
doi: https://doi.org/10.1080/14772019.2020.1768167
https://www.tandfonline.com/doi/full/10.1080/14772019.2020.1768167

https://pterosaurheresies.wordpress.com/2016/04/29/basal-archosauromorpha-paper-ezcurra-2016/

SVP 2018: More complete post-crania for Dromomeron

Smith, Irmis, Nesbitt and Turner 2018 report
on new Dromomeron material from the Petrified Forest, Late Triassic, Chinle Formation. Previously Dromomeron was known from a femur similar to that of Lagerpeton, a traditional dinosaur ancestor that nests with the chanaresuchid, Tropidosuchus in the large reptile tree (LRT, 1308 taxa; Fig. 1; Novas and Agnolin 2016).

Smith, et al., write:
“Discovery of the non-dinosauriform dinosauromorph Dromomeron romeri from the HQ established that early dinosauromorphs were contemporaries with dinosaurs for a substantial part of the Late Triassic, refuting hypotheses of rapid transition to dinosaur dominated faunas. This discovery was based on hindlimb elements, which diagnosed
Dromomeron as a member of Lagerpetidae, the sister group to all other dinosauromorphs.
Despite a flurry of new discoveries, the anatomy of lagerpetids remains poorly known. We
describe new specimens of Dromomeron romeri, including an articulated post-cranium,
further revealing lagerpetid anatomy.”

Importantly the foot of Dromomeron is different than that of Lagerpeton.
“An articulated metatarsus is short relative to the tibia, in contrast to the elongate metatarsus of Lagerpeton chanarensis and most dinosauromorphs. MTIII is the longest, with sub equal MTIV/MTII, and MTI 50% the length of MTII. This configuration differs starkly from the highly modified metatarsus of Lagerpeton.” 

Interesting that these authors seem to have ignored
the abstract from two years ago by Novas and Agnolin 2016, who also found Lagerpeton nested as a derived proterochampsid, confirming of an earlier blogpost here in 2011. No other proterochampsid has a longer metatarsal 3 than 4.

Archosauriform taxa with metatarsal 3 the longest:

1. Basal Dinosauria
2. Gracilisuchus (and no other crocs, which might mean Romer made a mistake)
3. Most erythrosuchids through poposaurs (many derived exceptions)
4. Champsosaurus

So maybe Dromomeron is a dinosaur. Not a lagerpetid.
That seems to be the most likely solution at this stage. No one wants to ‘Pull a Larry Martin’ and make a decision based on one or a few traits. Let’s see what a suite of traits gets us.

Figure 5. Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

References
Smith N, Irmis R, Nesbitt SJ and Turner AH 2018. New material of Dromomeron romeri (Archosauria, Dinosauromorpha) from the Upper Triassic Chinle Formatin of New Mexico provides insight into the evolutionary morphology of early dinosauromorphs. SVP abstracts.
Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

https://pterosaurheresies.wordpress.com/2016/11/13/you-heard-it-here-first-lagerpeton-is-not-a-dinosauromorph/

The real Proterochampsa

Drawings are great.
Reig (1959) gave us a drawing of Proterochampsa (Fig. 1), and it was good enough to nest it correctly. This is the best we’ve had for decades.

Figure 1. Proterochampsa as drawn by Reig 1959..

Photographs are better. 
Trotteyn (2011) was kind enough to include a photograph or three of the actual specimen (Fig. 2) in her PhD dissertation. It’s a little different, and provides great data.

Figure 2. The skull of Proterochampsa (PVSJ 77) colorized here for bone identification. The mandible was rotated during crushing. Tip of the mandible is oddly shaped, perhaps due to breakage. Not sure. Most of the teeth are broken at the root line. DGS provides a little more detail on a difficult skull. 

DGS provides a little more detail here. And we can trust the photo a little more than the drawing. It’s a shame they didn’t provide a photo decades ago.

The holotype (PVSJ 77) is only known from a skull. Earlier we looked at a much larger Proterochampsa (PVSJ 606) known from more complete material.

References
Reig OA 1959 Primeros datos descriptivos sobre nuevos Reptiles Arcosaurios del Triasico de Ischigualsto (San Juan, Argentina): Revista de la Asociacion Geologica Argentina, tomo 13, n. 4, p. 257-270.
Trotteyn MJ and Haro JA. In Press. The braincase of a specimen of Proterochampsa Reig (Archosauriformes: Proterochampsidae) from the Late Triassic of Argentina. Paläontologische Zeitschrift. Published on-line May 11 2010. DOI 10.1007/s12542-010-0068-7
Trotteyn MJ 2011. Material postcraneano de Proterochampsa barrionuevoi Reig, 1959 (Diapsida: Archosauriformes) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 48:424-446.
Trotteyn MJ 2011. Revisión osteologica, análisis filogenético y paleoecología de proterochampsidae (Reptilia – Archosauriformes). Tesis Doctoral. Instituto y Museo de Cienciea Naturales Universidad Nacional de San Juan. CONICET.

wiki/Proterochampsa

 

Diandongosuchus palate

Diandongosuchus fuyuanensis was originally (Li et al. 2012) nested with Qianosuchus and the poposaurids, but it shares very few traits with these taxa as blogged here. This middle Middle Triassic, croc-mimic was derived from a croc-like specimen of Youngina, BPI 2871 and a sister to Diandongosuchus gave rise to the parasuchians, Paleorhinus and Parasuchus. Proterochampsa was a sister and Diandongosuchus is not far from long-legged Chanaresuchus and Doswellia + Choristodera.

We looked at Diandongosuchus earlier here and in five other posts.

The palate is virtually invisible (Fig. 1), seen only through the naris, antorbital fenestra, orbit and a smidgeon between the jaws on the underside. The basisphenoid is not visible, probably hidden beneath a mandible. But the cultriform process is visible. So, with available data, here is the palate of Diandongosuchus reconstructed in a step-by-step process using the infamous DGS (digital graphic segregation), which I submit, still has value as shown below.

Figure 1. Using DGS to tease out the palate elements of Diandongosuchus. Color tracings enable the important elements of the skull to be layered upon one another to see where things match up and where they don’t. A sliver here might be connected to another sliver there. I was surprised to see how narrow the skull was, even before crushing.

Diandongosuchus is just another big, nasty, robust younginid, but developing along separate lines than Proterosuchus and Garjainia, which have a similar heritage. Converging with Gargainia, the skull of Diandongosuchus was taller than wide, which is different than all of its closest sisters.

The deep cheeks in this taxon are further developed in parasuchians, which raised the orbit to the top of the skull. The vomers are very long and I suspect that the maxillary palatal plates supported it. You can see rather plainly in Chanaresuchus, in which the internal nare are divided into fore and aft openings by the advancing maxilla. In parasuchia the vomer is very short because the premaxilla is very long.

References
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

wiki/Diandongosuchus

Diandongosuchus – another giant younginid

Earlier we looked at Diandongosuchus, which was originally considered a poposaurid (Li et al. 2012). The large reptile tree (now needs to be updated) nested Diandongosuchus at the base of the parasuchians and proterochampsids (including the biped, Lagerpeton). It’s easy to see the resemblance.

Today we’ll revise the skull of a tiny Youngina, BPI 2871, which is the basal taxon in this lineage (more primitive than Diandongosuchus). Seems the rostrum of the BPI specimen was probably crushed dorsoventrally, resulting in a false concave rostral profile. The posterior skull is missing, but it can be restored closer to Diandongosuchus now that the phylogenetic analysis shows the close relationship.

Figure 1. The large reptile tree nests these two taxa as sisters despite their size difference. With greater size came the development of an antorbital fenestra, independent of the one developing in other Younginids leading toward archosauriformes beginning with Proterosuchus.

Evolution works in baby steps.
That’s why maximum parsimony (fewest morphological changes) is still the best route for finding ancestors and descendants and for filling in missing parts by the method of phylogenetic bracketing. Diandongosuchus also gives us clues as to the post-crania of the BPI 2871 specimen of Youngina, with reservations regarding the great size difference.

I’d like to see the BPI 2871 specimen, but the last I heard (several years ago) it was ‘on loan’ and had not been returned.

Some workers, Gow (1975), among them, consider the BPI 2871 specimen congeneric with other Youngina and Younginoides specimens, with all apparent changes in morphology due to crushing. While that is likely true to a certain extent, there are differences that can be scored in phylogenetic analysis to reveal their differences and relationships. And you can always take out the crushing to check out prior hypotheses.

Earlier we looked at Garjainia as another giant younginid.

References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom andProlacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

wiki/Diandongosuchus
wiki/Youngina

A new Doswellia snout!~!

Traditional paleontologists are still a little off about Doswellia (Fig. 1). It is a strange one with transverse and square ribs, a horizontal ilium, and a low wide skull that fills in a former lateral temporal fenestra. Unfortunately the rostrum has not been known for the last 30 years. Neither have the feet.

Even so, the large reptile tree firmly nested Doswellia at the base of the Choristodera, derived from Youngoides (RC91) and more distantly related to taxa at the base of the Parasuchia and Proterochampsia, all members of the Pararchosauriformes.

Figure 1. Doswellia in several views from Weems (1980). Missing pieces from 1980 are in black.

News about the rostrum!
Thankfully Heckert et al. (2012) discovered some of the last missing pieces, the premaxilla and maxilla of Doswellia (Fig. 2). Unfortunately they could not bring more focus to relationships, but repeated Dilkes and Sues (2009) assessment that Doswellia was close to proterochampsids, again ignoring the Choristodera and younginoids.

Figure 2. The newfound elements of Doswellia found by Heckert et al. (2012). The naris is dorsal. A tiny antorbital fenestra is present. The ventral maxilla is wavy. The premaxilla is deeper anteriorly and tips downward.

So what’s new?
The maxilla has teeth of several sizes and the ventral margin is wavy, not straight as in sister taxa.

There is an antorbital fenestra, small, and without much of a fossa. This follows the pattern seen in some (but certainly not all) Youngina and proterochampsids, and not seen  in the Choristodera.

The naris is dorsal in position, but still at the jaw tips. This is totally in line with the entire clade, which, other than Champsosaurus, all have dorsal nares. The premaxilla is also deeper anteriorly, downturned at the tip, as in several sisters.

The teeth are stout cones ideal for capturing prey.

This is a welcome discovery by Heckert et al. (2012) and fills a minor gap with real data. Glad to see it. Thanks to Dr. Heckert for sending the pdf.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Dilkes D and Sues H-D 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29(1):58-79.
Heckert AB, Lucas SG and Spielmann JA 2012. A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA”. Palaeontology (Blackwell Publishing Ltd) 55 (6): 1333––1348. 
Weems RE 1980. An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A. Transactions of the American Philosophical Society, New Series 70(7):1-53

wiki/Doswellia

Still working on Diandongosuchus

Sorry for the lack of a regular post today.
On Saturday you’ll see a reconstruction of Diandongosuchus, the new basal phytosaur. We’ll make graphic comparisons to Qianosuchus, poposaurs, phytosaurs, proterochampsids and champsosaurs. So you’ll see why the large reptile tree nests Diandongosuchus with the phytosaurs, not the poposaurs.

Thank you for your patience. It will be rewarded.

In the meantime, there’s a doggone good restoration of Diandongosuchus here.

Proterochampsia Paper

David Dilkes was kind enough to send his new paper on Proterochampsa (Dilkes and Arcucci 2012). His tree follows traditional nestings (Fig. 1). Dilkes and Arcucci (2012) also describe the long journey this odd branch has taken as new taxa were slowly added over the years. Makes interesting reading.

Figure 1. Proterochampsia tree by Dilkes and Arcucci (2012). Green added to highlight relationships recovered by the large reptile tree (Fig. 2). Some notes added in blue and red highlight missing and “by default” taxa that should not be included. Not sure why parasuchians don’t nest closer to proterochampsids here as they often do in other trees, including the large reptile tree. Euparkeria seems out of place there, but does nest close to Riojasuchus in other trees.

Unfortunately, one again, too few taxa were added to this tree to recover the same relationships recovered by the large reptile tree (Fig. 2) in which all sister taxa share larger suites of traits. In the Dilkes and Arcucci (2012) tree you get such odd pairings as Doswellia and Vancleavea, Riojasuchus and Aetosaurus, Euparkeria and Parasuchus among others. Only the taxa within the focus group, the Proterochampsia (node D), are true sisters also recovered by the large reptile tree.

Wisely, Dilkes and Arcucci (2012) left out pterosaurs, which are often nested close to parasuchians and proterochampsids. Unfortunately they left out Lagerpeton, members of the Choristodera and several Youngina/Youngoides specimens, all of which would have helped clarify relationships, according to the large reptile tree.

Figure 2. Left: A segment of the large reptile tree showing what happens when more taxa are included. The Pararchosauriformes form a branch separate from the Euarchosauriformes and develop an antorbital fenestra and foss by convergence. Right: Reducing the branch on the left to include only those taxa chosen by Dilkes and Arcucci (2012) with the addition of the thalattosaur, Vancleavea, mistakenly chosen for inclusion by Dilkes and Arcucci (2012). Here more parsimony in sister taxa, but several forced nestings further toward the base of the tree.

A segment of the large reptile tree (Fig. 2) recovers a different topology because more taxa are included. In the large reptile tree the Proterochampsia were more closely related to parasuchians and choristoderans. All share a dorsal, posteriorly-displaced naris (reversed in Champsosaurus as a snorkel), and several other synapomorphies.

A Distinct Convergent Antorbital Fenestra
We discussed earlier the four times the antorbital fenestra was developed. Check it out. We also earlier discussed the nesting of the large proterochampsid (Fig. 3),

Figure 3. A new specimen attributed to Proterochampsa alongside the holotype specimen.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Dilkes D and Arcucci A 2012. Proterochampsa barrionuevoi (Archosauriformes: Proterochampsia) from the Late Triassic (Carnian) of Argentina and a phylogenetic analysis of Proterochampsia.  Palaeontology (advance online publication) 1-33. doi: 10.1111/j.1475-4983.2012.01170.x

A New Proterochampsa? This Time with Postcrania!

For several decades all we knew of Proterochampsa barrionuevoia (Reig 1959) consisted of several skulls and cervical vertebrae. The rest of the postcranium remained unknown until now. A new report by Trotteyn (2011) reveals much of the missing post-crania. PVSJ 606 was at least twice as large as the holotype (Fig. 1). It was found in the Ischigualisto Formation of the Late Triassic.

Figure 1. A new specimen (PVSJ 606) attributed to Proterochampsa by Trotteyn (2011). Lateral view from Trotteyn (2011). Dorsal view after tracing the skull image in Trotteyn (2011).

Proterochampsa nodosa
A third specimen and a separate species, P. nodosa, I have not seen yet. The abstract distinguishes the two species, “..snout becoming narrow anteriorly in a less gradual manner than in P. nodosa, lower occiput, nares lanceolate with narrow anterior and posterior ends, and frontal less irregular that in P. nodosa.”

Figure 2. Bone identification in a dorsal view of the skull PVSJ 606.

Comparisons
Due to the compressed skull of PVSJ 606 and its attribution, I expected the post-crania to be likewise compressed with short legs, perhaps most similar to basal parasuchians, like Parasuchus. As it turns out, the post-crania more closely resembled that of Chanaresuchus.

Figure 3. The Pararchosauriformes. Click to see entire tree. Note the nesting of the new specimen attributed to Proterochampsa as a sister to the holotype, but at the base of the chanaresuchids.

Description
The skull of PVSJ 606 (Fig. 2) was relatively enormous! It was as long as the presacral vertebral column. The various fenestrae were relatively smaller. The premaxilla was shorter and the post-orbital area was more robust. The premaxilla was not squared off. Do these differences, plus the major size difference mean the new specimen is a new species? Unfortunately Trotteyn (2011) completely ignored comparisons to the holotype skull, focusing all her efforts on a description of the post-crania alone.

The cervicals and caudals were more gracile in PVSJ 606 than in sister taxa. This seems improbable considering the size of the skull, but true. The torso was rather short and the legs were rather long.

Ecology and Behavior
No one has figured out the ecology and behavior of Proterochampsa or this specimen. Not sure what to make of it yet. It’s a bizarre creature!

Analysis
Trotteyn (2011) did not published a cladistic analysis having opted instead to synonymize the new specimen with the holotype of Proterochampsa. Under cladistic analysis PVSJ 606 nested as a sister to Proterochampsa (Fig. 3) at the base of the Cerritosaurus clade that also includes Chanaresuchus. So, PVSJ 606 is likely not congeneric or conspecific with Proterochampsa. It takes 8 extra steps to create a sisterhood with the holotype.

Figure 4. DGS reveals two other digits and metatarsal 5 not described in the pes of Proterochampsa hidden among the skull bones. See Figure 1 for a reconstruction.

The Pes
Only two toes (including their metatarsals) were described by Trotteyn (2011). Examination of the photograph (Fig. 2) appears to show two more toes plus metatarsal 5 on the skull, which is somewhat fragmented, but largely intact. The  reconstructed elements create what appears to be a valid pes with continuous PILs (Fig. 1). Are these interpretations valid or not? Send data! We’ll figure this out. I’m only working from published photos in black and white.

An Ancestral Sister to Pterosaurs and Dinosaurs?
A recent report on archosaur relations (Brusatte et al. 2010) placed Proterochampsa at the base of the clade that produced dinosaurs and pterosaurs. Ridiculous for dozens of reasons, yet this was one of many such studies with similar results. Unsupportable and illogical results such as these are a direct result of inappropriate exclusions and inclusions in the taxon list resulting in “by default” nestings.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Reig OA 1959 Primeros datos descriptivos sobre nuevos Reptiles Arcosaurios del Triasico de Ischigualsto (San Juan, Argentina): Revista de la Asociacion Geologica Argentina, tomo 13, n. 4, p. 257-270.
Trotteyn MJ 2011. Material postcraneano de Proterochampsa barrionuevoi Reig, 1959 (Diapsida: Archosauriformes) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 48:424-446.

wiki/Proterochampsa