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.

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 ChampsosaurusSimoedosaurus and Diandongosuchus.

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

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.

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.

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

Doswellia in several views

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.

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.

Reconstruction and restoration of the skull and neck of Jaxtasuchus, along with scattered armor. The long neck and slender cervical ribs are protorosaur traits. The antorbital fenestra is shared with Pamelaria (fig. 2).

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.

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.

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, these are among the most complete segments known of this reptile.

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.

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.

Doswellia in several views

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.

The newfound elements of Doswellia found by Heckert et al. (2012).

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

More About Doswellia and Archeopelta

The phylogenetic position of Doswellia (Weems 1980) has been troublesome because it is so different from other Triassic reptiles. Recent cladistic analyses (Desojo, Ezcurra  and Schultz 2011) have shed light on the nesting of Doswellia and the large study has nailed it down.

Doswellia in several views

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

Doswellia Basics
As a diapsid, Doswellia lost its lateral temporal fenestrae. The orbits were on top of the flattened skull. The missing rostrum was narrow and elongated if it fit the narrow and elongated mandible. The posterior mandible was deeper than the skull. Different than its sisters, the Doswellia ilia have rotated laterally such that the lateral surface now faces ventrally. The posterior dorsal ribs extended only laterally matching the elongated transverse processes of the anterior caudals. The anterior dorsal ribs extended laterally then abruptly turned ventrally at mid-length. The femur was relatively short, indicating a low-slung configuration. The seven cervicals were elongated such that the elongated, but relatively small skull was shorter than the cervicals.

That Very Strange Ilium Compared
(Desojo, Ezcurra  and Schultz 2011) compared the ilium of Doswellia (updated from Weems 1980) to several other reptiles. Unfortunately they included several unrelated taxa (Mesosuchus, Vancleavea and Erythrosuchus) and excluded Champsosaurus and Youngoides RC91, two Doswellia sisters in the large study. Fortunately Proterochampsa was tested against Doswellia and it nests as a close sister, but unfortunately no ilium has been published for this taxon. In this case, there were no closely related taxa with a similar ilium. Thus Doswellia is alone with regards to its ilium.

Fortunately the large study relies on a large suite of characters. Until a closer sister taxon comes along, Doswellia will continue to nest between Youngoides and Champsosaurus, with Archeopelta closer (but not yet included in the large study).

Comparing ilia to that of Doswellia.

Figure 2. Comparing various ilia to that of Doswellia (in pink). Desojo (2011) included an unrelated lepidosaur, Mesosuchus, an unrelated thalattosaur, Vancleavea, and an unrelated euarchosauriform, Erythrosuchus due to poor prior poorly assembled inclusion sets. Chanaresuchus is the closest sister in the top row and there was no resemblance. On the bottom row are Youngina and Champsosaurus, two closer sisters to Doswellia and even here there was no distinct synapomorphy. The ilium of Doswellia was oriented laterally, not vertically, like the others and that difference sets Doswellia apart from all known sister taxa. The ventral pelvis was medially oriented in Champsosaurus and Doswellia and the acetebulum was partly open ventrally.

Archeopelta
Archeopelta
 (Desojo, Ezcurra  and Schultz 2011) is known from less complete material (dorsals and a few other nearby parts), but appears to be the closest known sister with regard to a suite of characters not listed in the large study.

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
Desojo JB, Ezcurra MD and Schultz CL 2011. An unusual new archosauriform from the Middle–Late Triassic of southern Brazil and the monophyly of Doswelliidae. Zoological Journal of the Linnean Society, 2011, 161, 839–871. DOI: 10.1111/j.1096-3642.2010.00655.x
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.
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