Rugarhynchos: Late Triassic archosauriform really close to Doswellia

A former Doswellia sp.
(Heckert et al. 2012) has be reexamined and renamed Rugarhynchos sixmilensis by Wynd et al. 2020.

The resemblance is remarkable
(Fig. 1) and the size is similar. Both are from the Late Triassic of North America (Virginia and New Mexico). Wynd et al. did a good job of tracing the bones, but provided no reconstructions (they pictured the premaxilla on a separate page spread). They also misidentified the surangular (SA) as the quadratojugal.

Is this just another species of Doswellia?
We’ve seen more variation in Rhamphorhynchus, and Pteranodon, but naming a new genus is reserved for full professors and their students. In this case, the resemblance is readily apparent, and so are the various enlargements and reductions. The problem lies, as it often does, in the published cladogram (Fig. 2) suffering from taxon exclusion.

Figure 1. Doswellia skull compared to Rugarhynchos, here reduced to a similar length for rapid comparison.

From the abstract:
“Stem archosaurs exhibit substantial cranial disparity, especially by taxa either shortening or elongating the skull. This disparity is exemplified in the North American Late Triassic proterochampsians by the âshort-facedâ Vancleavea and the ong-faced doswelliids.”

When more taxa are added, as in the large reptile tree (LRT, 1695+ taxa; subset Fig. 3), Vancleavea nests with Helveticosaurus in the Thalattosauria, as we learned several years ago. Missing from the Wynd et al. taxon list are any choristoderes. Those are close relatives to doswellids in the LRT.

“To critically investigate skull elongation and character evolution in these proterochampsians, we evaluate Doswellia sixmilensis, known from much of a skull, cervical centra, and osteoderms from the Bluewater Creek Member of the Chinle Formation of New Mexico.” (See Fig. 1).

Figure 2. Cladogram from Wynd et al. 2020 with colors added to show where these taxa nest when more taxa are added, as in the LRT. Avemetatarsalia is invalid because it includes both pterosaurs and dinosaurs, neither of which is related to Vancleavea or Phytosauria in the LRT. Remember to check your results for mismatches like this.

From the abstract:
“Rugarhynchos sixmilensis, gen. et comb. nov., exhibits an elongate snout with characteristics known in stem and crown archosaurs, including a downturned premaxilla and fluted teeth.”

In the LRT, archosaurs include only crocs + dinos (including birds). Due to taxon exclusion (chiefly bipedal basal crocodylomorphs) Wynd et al. expand that list to include many other taxa.

“We included R. sixmilensis in a phylogenetic analysis of archosauromorphs consisting of 677 characters and 109 taxa under both parsimony and Bayesian models.”

Now do you see why increasing the number of taxa is MUCH more important than increasing the number of characters? How one taxon relates to other taxa requires a lot of other taxa… and a sufficient number to traits (150+). The LRT includes 238 multi-state taxa and it nests everything from fish to humans with high resolution.

“We recover R. sixmilensis as a doswelliid, sister to Doswellia kaltenbachi. Our parsimony and Bayesian models differ in the placement of Doswelliidae, either as sister to or within Proterochampsidae, respectively.”

Wynd et al. excluded too many pertinent taxa. Here’s where the LRT (Fig.3) nests Doswellia and the pararchosauriformes.

“We use archosauromorph relationships from the Bayesian model to estimate cranial disparity between stem and crown archosaurs and find a narrow breadth of morphological disparity in the stem. Our results suggest that crown archosaurs evolved disparate crania from a low-disparate archosauriform condition.”

Without a valid phylogenetic context (Fig. 3), the results of Wynd et al. cannot be validated. They need more taxa.

Figure 3. Subset of the large reptile tree focusing on the pararchosauriformes and the Choristodera, still similar since 2015. Euparkeria is basal to the Euarchosauriformes, including Archosauria.

The skull of Rugarhynchos was added to a graphic
(Fig. 4) that included Doswellia and its relatives to scale. Many of these taxa were omitted from Wynd et al. 2020.

Figure 4. 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.

Wynd et al. considered Rugarhynchos a proterochampsid.
With more taxa added (Figs. 3, 4) that’s not confirmed by the LRT. Doswellia is slightly closer to choristoderes, a clade not shown in the Wynd et al. cladogram (Fig. 2). It would have been better if Wynd et al also added a variety of proterosuchids, as in the LRT. They are all as different and distinct as Rugarhynchos is from Doswellia.

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References
Wynd BM, Nesbitt SJ, Stocker MR and Heckert AB 2020. A detailed description of Rugarhynchos sixmilensis, gen. et comb. nov. (Archosauriformes, Proterochampsia), and cranial convergence in snout elongation across stem and crown archosaurs. Journal of Vertebrate Paleontology Article: e1748042
doi: https://doi.org/10.1080/02724634.2019.1748042
https://www.tandfonline.com/doi/full/10.1080/02724634.2019.1748042

SVP 2018: Doswellia skull chimaera reconfigured

Wynd, Newbitt and Heckert 2018
“redescribe Doswellia sixmilensis on the basis of extensive repreparation of the skull material to identify cranial elements, morphological details previously not described, and cranial suture patterns. As such, we reinterpret what was previously regarded as the antorbital fenestra to be the orbit and, as a consequence, the identification of bones and the diagnosis of the taxon must be substantially modified.”

Today I learned
the larger rostrum was attributed to a second Doswellia species, D. sixmilenesis. (Heckert et al. 2012). The reconstructions below created a chimaera of the two skulls, and two reconstructions based on the old and new interpretations of the larger rostrum.

Figure 1. Doswellia restored two ways using two species. In this restoration, the pmx ascending process is gracile and missing, along with the anterior naris. The insert shows the vestige of the lateral temporal fenestra. If the large specimen includes an orbit and jugal here is a new reconstruction reflecting that change.

Either way
the sum of the parts largely match sister taxa (Fig. 2) in the large reptile tree (LRT, 1315 taxa).

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciate the similarities and slight differences that are gradual accumulations of derived traits.

The taxon list for the abstract
was not published, but I hope it includes the taxa used in the LRT where Doswellia nests closer to certain proterochampsids than to proterochampsids.

The authors report,
“What is clear, is that D. sixmilensis shares character states with typical proterochampsians (e.g., rimmed orbit) that are not found in D. kaltenbachi.” In the first (earlier) reconstruction (Fig. 1), the orbits were not preserved, except ventrally by the large jugal.

Figure 3. 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.

The genus Doswellia
is distinct from all other genera, but trait scores nest it closest to a derived proterosuchid, the SAMPK K10603 specimen (Figs. 1, 2).

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 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.
Wynd BM, Nesbitt SJ, Heckert AB 2018. Skull elongation in stem archosaur cranial displarity: Reevaluationg Doswellia sixmilensis (Archosauriformes: Proterochampsia) to examime phylogenetic distribution of morphological disparity. SVP Abstracts.

wiki/Doswellia

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

Is this the real nose of Doswellia?

The preserved portion of the Doswellia premaxilla is so odd, I wondered if it was incomplete. Maybe the preserved portion is only the palatal portion of the premaxilla. The tiny holes are then best considered sinus openings, rather than nares. If so it might have looked like this. Now, not so odd. The posterior portion of the long premaxillary ascending process may even be present at mid rostrum (the diagonal yellow strip).

Figure 1. Doswellia nose restored to match that of sister taxa. In this restoration, the pmx ascending process is gracile and missing, along with the anterior naris. Now it’s not so odd.

Earlier we looked at Doswellia here (updated) and here (not updated).

 

The droopy snout of Doswellia

UPDATED
on April 2, 2014 with new data on the pmx/mx suture and pmx ascending process.

Earlier, we looked at that odd archosauriform, Doswellia (Late Triassic, Weems 1980, Dilkes and Sues 2009, Heckert et al. 2012). It was originally considered a sister to Proterochampsidae, which is very close. The large reptile tree nested it as a basal, but not very plesiomorphic, choristodere, derived from a sister to Youngina BPI 2871 (Fig.1 ) and otherwise close to Champsosaurus, Simoedosaurus and Diandongosuchus.

Figure 1. The sister to Doswellia, the BPI2871 specimen of Youngina.

Earlier I accepted the straight mandible reconstruction of Weems (1980) and Heckert et al. (figure 6, 2012).

However, the mandible illustrated alone in Dilkes and Sues (2009) is ventrally concave. Putting that into a reconstruction (Fig. 2) also matches the referred broken rostrum of Heckert et al. (2012).

The Droopy Snout
Convergent with Proterosuchus (Fig. 3), Doswellia had a droopy snout that started to droop at mix maxilla, instead of a the pmx/mx suture.

 

Figure 2. Click to enlarge. Doswellia reconstructed from bone pieces. The postfrontal and postorbital are fused but colored separately. A tiny lateral temporal fenestra remains. The larger specimen may have had a stronger curve in the rostrum.

Doswellia is reported to have lost lateral temporal fenestrae, but tiny vestiges are still apparent (Fig. 1). Small antorbital fenestra are present, but they appear to be vestiges, on their way to disappearing, too. Choristoderes do not have antorbital fenestra.

FIgure 3. Proterosuchus (above) and Doswellia (below). Note the similarity of the drooping premaxilla, the shape of the pes and the overall low slung body.

The nares
are at the tip of the snout, but dorsolateral with a short premaxilla. We also see something like this in champsosaurus. The posterior portion of the ascending process of the premaxilla appears to be present, stuck to the side of the maxilla due to taphonomic forces.

This new reconstruction comes from transferring existing drawings using DGS (digital graphic segregation) to create a reconstruction. Color also helps.

And this is blog post #900.

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.
Sues H-D, Desojo JB and Ezcurra MD 2013. Doswelliidae: a clade of unusual armoured archosauriforms form the Middle and Late Triassic. Geological Society, London
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

Doswellia: Taxon Exclusion Problems in Sues et al. 2013

Figure 1. Doswellia in several views from Weems (1980).

Sues et al. (2013) took a long, hard look at Doswellia, but still missed the boat due to taxon exclusion. In the large reptile tree Dosweliia nests as a basal choristodere, but no choristoderes were tested in Sues et al. (2013). Moreover, choristoderes are derived from Youngina and Younginoides in the large reptile tree, but none of these taxa were included in the Sues et al. (2013) study. Finally no phylogenetic study looked at by Sues et al. (2013) recognized the divergence of Parachosauriformes (including Doswellia and kin) and Euarchosauriformes. These are basic problems.

Figure 2. Basal Pararchosauriformes includingin Youngina, Doswellia, Cteniogenys and Gualosuchus.

It’s hard to figure out what Doswellia is when the closest known sisters (Fig. 2) are ignored.

Earlier we talked about Doswellia relationships here. and here.

References
Sues H-D, Desojo JB and Ezcurra MD 2013. Doswelliidae: a clade of unusual armoured archosauriforms form the Middle and Late Triassic. Geological Society, London,

Jaxtasuchus – a new protorosaur, not a doswelliid

A new paper by Schoch and Sues (2013)
introduces a new armored archosauriform with long teeth, Jaxtasuchus salomoni (Fig. 1). It was considered semi-aquatic because it was found in Middle Triassic mudstones along with amphibians, crustaceans, and mollusks. Several incomplete skeletons are known. Schoch and Sues (2013) ran a phylogenetic analysis of 17 taxa that nested Jaxtasuchus with doswelliids, which were similarly armored. Unfortunately, that tree also nested several strange-bedfellows together, including Mesosuchus with Prolacerta, Vancleavea with Chanaresuchus, Parasuchus with Stagonolepis and Scleromochlus with Marasuchus none of whom resemble their putative sisters.

Maybe not a doswelliid
Adding what little is know of Jaxtasuchus to the large reptile tree nests it firmly with Pamelaria, a protorosaur. Protorosaurs are known for their elongated necks, but not for their armor.

In any case, it takes 10 more steps to move Jaxtasuchus to Prolacerta (which was included in the Schoch and Sues (2013) phylogenetic analysis) and 14 steps to move Jaxtasuchus to Doswellia. If valid, the long teeth and armor of Jaxtasuchus would be protorosaur autapomorphies that add new variety to this clade.

Figure 1. Reconstruction and restoration of the skull and neck of Jaxtasuchus (based on Schock and Sues 2013), along with scattered armor. The long neck and slender cervical ribs are protorosaur traits. The antorbital fenestra is shared with Pamelaria (fig. 2). No other known protorosaur has such long teeth and armor.

A new fifth instance of an antorbital fenestra!
Perhaps even more exciting than armor, Jaxtasuchus was described with an antorbital fenestra lacking a fossa. Doswellia (Heckert et al. 2012) likewise has a tiny antorbital fenestra, but not similar in design. However, a reexamination of Pamelaria reveals a very similar maxilla to Jaxtasuchus, which means it also had a previously overlooked antorbital fenestra (Fig. 2). Together these two up the total number of novel inventions of the antorbital fenestra from four to five. That’s a big deal.

Figure 2. The skull of Pamelaria from Sen 20003, with the maxilla highlighted in green. The maxilla appears similar to that in Jaxtasuchus in having an antorbital fenestra. Teeth are only present along the posterior portion of the maxilla.

Restoring the manus and pes
I reconstructed the pes and manus of Jaxtasuchus using PILs (parallel interphalangeal lines). On both the manus and pes proximal phalanges were all longer and distal phalanges were all subequal.

Figure 3. The manus and pes of Jaxtasuchus restored. Along with the cervicals (Fig. 1), these are among the most complete segments known of this reptile.

The osteoderms have a longer history
The osteoderms of Jaxtasuchus were previously interpreted as coming from temnospondyl amphibians or aetosaurs. Remains of Jaxtasuchus have been found in five localities and have been considered common. Now, courtesy of Schoch and Sues (2013) we know enough about it to consider it an armored predator with an antorbital fenestra. Thanks to the large reptile tree, which includes virtually every basal reptile clade, we can consider Jaxtasuchus a new protorosaur, rather than a doswelliid.

Figure 4. Click to enlarge. Jaxtasuchus reconstruction with armor. The small limbs might suggest a sinuous mode of locomotion, but the armor would argue against that. Perhaps this was a sit-and-wait predator, convergent with tanystropheids. The skull and neck specimen appear to come from a larger one than the post-crania, hence the estimate to match. 

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
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.
Sen K 2003. Pamelaria dolichotrachela, a new prolacertid reptile from the Middle Triassic of India. Journal of Asian Earth Sciences 21: 663–681.
Schoch RR and Sues H-D (2013). A new archosauriform reptile from the Middle Triassic (Ladinian) of Germany. Journal of Systematic Palaeontology (advance online publication) DOI:10.1080/14772019.2013.781066 online

wiki/Jaxtasuchus

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