Armadillosuchus: another small herbivorous croc

Marinho and Carvalho 2009
brought us a new, small, crocodyliform from the Late Cretaceous of South America, Armadillosuchus (Fig. 1).

Oddly,
the nares are not mentioned in the text, nor labeled in the published figure (Fig. 1). Where are they?

Figure 1. Armadillosuchus skull in dorsal view and lateral view. A second specimen preserves teeth. Reconstruction below aligns the ventral maxilla with the quadrate, as in all sister taxa.

Figure 1. Armadillosuchus skull in dorsal view and lateral view. A second specimen preserves teeth. Reconstruction below aligns the ventral maxilla with the quadrate, as in all sister taxa. Where are the nares? They are not mentioned in the text.

Armadillosuchus arrudai (Marinho and Carvalho 2009; Late Cretaceous; est. 2m in length) was an herbivorous and armored crocodylomorph from South America. It nests with Mariliasuchus (above) in the LRT. Both have giant premaxillary teeth. The naris is reduced to a tiny hole facing anteriorly. The rostrum may have been more horizontal than originally reconstructed as all sister taxa line up the quadrate with the ventral maxilla (Fig. 1 bottom figure). These are members of the Ziphosuchia.

Figure 1. Mariliasuchus skull in several views. Note the premaxillaery fangs and the short blunt remainder of the teeth.

Figure 2. Mariliasuchus skull in several views. Note the premaxillaery fangs and the short blunt remainder of the teeth. The nares are very tiny and anteriorly oriented. Note the alignment of the quadrate with the ventral rim of the maxilla together with the rostrum vs. forehead angle, as in the new lateral view of Armadillosuchus (Fig. 1).

The nares of Armadillosuchus
are best found by phylogenetic bracketing based on the nares found in its sister taxon Mariliasuchus (Fig. 2).

Figure 2. Subset of the LRT focusing on Crocodylomorpha (basal Archosauria) including Armadillosuchus.

Figure 2. Subset of the LRT focusing on Crocodylomorpha (basal Archosauria) including Armadillosuchus.

Key to understanding the origin of the clade Dinosauria
is to understand the proximal outgroup taxa, the bipedal basal Crocodylomorpha, which no prior studies include (though some include Lewisuchus).

Images of complete skeletons of Armadillosuchus
are online, photographed from museum mounts. I have not found academic data for anything more than is figured above. The rest may be restored. Let me know of any citations I have missed.

References
Marinho T S and Carvalho, IS 2009. An armadillo-like sphagesaurid crocodyliform from the Late Cretaceous of Brazil. Journal of South American Earth Sciences. 27 (1): 36–41.

wiki/Mariliasuchus
wiki/Armadillosuchus

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Enigma archosauriforms pt. 3/3: Erpetosuchus and kin

According to Wikipedia
Erpetosuchidae is an extinct family of pseudosuchian archosaurs. Erpetosuchidae was named by D. M. S. Watson in 1917 to include Erpetosuchus and Parringtonia gracilis from the middle Middle Triassic of Tanzania. The group might also include Dyoplax arenaceus from the Late Triassic of Germany,[3] Archeopelta arborensisPagosvenator candelariensis from Brazil and Tarjadia ruthae from Argentina.

In the large reptile tree
(LRT, 1206 taxa, subset Fig. 6) only Erpetosuchus (Fig. 1) and the taxa listed below nest together. The other taxa listed above nest elsewhere (see Fig. 6).

What we know of Erpetosuchus, a basal crocodylomorph.

Figure 1. What we know of Erpetosuchus, a basal crocodylomorph from the Late Triassic. The skull is quite derived.

Erpetosuchus granti (Newton 1894) Late Carnian, Late Triassic, ~60 cm in length. Only the front half of Erpetosuchus is known. Erpetosuchus was derived from a sister to Tarjadia. Perhaps Erpetosuchus represented the last of its lineage, judging by its odd morphology. Distinct from Tarjadia the skull of Erpetosuchus was most unusual in palatal view where the maxillae and jugals expanded medially to produce wide flat plates that crowded the pterygoid, palatine and ectoptergyoid together in the middle. Teeth erupted only in the anterior jaws. The orbits opened dorsally.

Figure 2. Litargosuchus is a bigger sister to Erpetosuchus in the LRT.

Figure 2. Litargosuchus is an Early Jurassic bigger sister to Erpetosuchus in the LRT. The differences with Erpetosuchus are strong, but no other taxon pair is more similar to each other in the LRT.

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. Clark and Sues were unable to resolve their family tree, but they did not include relevant taxa. Like Terrestrisuchus, the skull of Litargosuchus had uniquely convex temples.

Figure 1. Terrestrisuchus is a bipedal basal crocodylomorph with elongate proximal carpals.

Figure 1. Terrestrisuchus is a bipedal basal crocodylomorph with elongate proximal carpals.

Terrestrisuchus gracils (Crush 1984) Ladinian, Late Triassic (~210 mya), 50 cm long, was derived from a sister to SMNS 12591 at the base of the crocodylomorphs. It preceded Litargosuchus. Distinct from SMNS 12591 the skull of Terrestrisuchus was even narrower surrounding the upper temporal fenestrae and had an even lower rostrum. Compared to more primitive ancestors, the cervicals were longer, the dorsals and caudals were more gracile. The coracoid was a parallelogram in shape. Every element of the forelimbs was greatly elongated, but were short in comparison to the hind limbs.

FIgure 4. Erpetosuchids according to the LRT, all to scale below in white.

FIgure 4. Erpetosuchids according to the LRT, all to scale below in white. This clade shows two evolutionary paths, one quadrupedal and large, except for tiny Erpetosuchus, the other small and bipedal.

Tarjadia ruthae (Arcucci et al. 1998; Ezcurra et al. 2017; Middle Triassic) According to Wikipedia, “Prior to 2017, most studies placed it outside Archosauria as a member of Doswelliidae. The 2017 specimens instead show that it belonged to the Erpetosuchidae.”

Figure 5. Erpetosuchids skulls. Pink arrows show two evolutionary paths.

Figure 5. Erpetosuchids skulls. Pink arrows show two evolutionary paths, one quadrupedal and large except for tiny Erpetosuchus (see figure 4) the other small and bipedal. See below for phylogenetic inconsistency. 

Parringtonia gracilis (Huene 1939; Middle Triassic) was traditionally considered close to Erpetosuchus, even when just a few bone scraps were known. Recent finds (Nesbitt and Butler 2012) have filled out the rest of the skeleton.

Figure 6. Cladogram of basal archosaurs and kin. Yellow taxa are traditional members of the Erpetosuchidae, not confirmed as monophyletic here.

Figure 6. Cladogram of basal archosaurs and kin. Yellow taxa are traditional members of the Erpetosuchidae, not confirmed as monophyletic here.

Sharp-eyed readers will note
that the tree nests Erpetosuchus with Litargosuchus, not with Tarjadia. Some of the LRT traits Erpetosuchus shares with Litargosuchus, exclusive of Tarjadia include the following:

  1. Rostrum is straight angled, not convex and curved
  2. Nasal is hourglass-shaped in dorsal view
  3. Ventral premaxilla is oriented up distally
  4. Length is under 60cm
  5. among others…likely by convergence

On the other hand,
it is clear than the skull of Erpetosuchus shares several traits with Tarjadia, exclusive of Litargosuchus. The following cherry-picked synapomorphies are not listed as characters in the LRT.

  1. Posterior maxilla undercut with cheek region
  2. Maxillary teeth restricted to anterior half of the maxilla
  3. Upper temporal fenestrae wider than long
  4. Antorbital fossa larger than orbit
  5. Mandible not gracile
  6. Three processes extend from squamosal in lateral view
  7. Posterior skull widest posteriorly
  8. among others…

These trait lists support the value of reconstructions
to make comparisons in a visual mode to reveal issues not covered by the present character list. I’m going to need hi-rez photographs of all relevant taxa to sort this out. At present, only drawings serve as data.

References
Allen D 2003. When Terrestrisuchus gracilis reaches puberty it becomes Saltoposuchus connectens!”. Journal of Vertebrate Paleontology 23 (3): 29A.
Benton MJ and Walker AD 2002. Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland, Zoological Journal of the Linnean Society 136:25-47.
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.
Crush PJ 1984. A late upper Triassic sphenosuchid crocodilian from Wales. Palaeontology 27: 131-157.
von Huene F 1921. Neue Pseudosuchier und Coelurosaurier aus dem Wurttembergischen Keuper: Acta Zoologica, v. 2, p. 329-403.
Newton TE 1894. Reptiles from the Elgin Sandstone—Description of two new genera. Philosophical Transactions of the Royal Society of London, B, 185:573–607.
Olsen PE, Sues, H-D and Norell MA 2000. First record of Erpetosuchus (Reptilia: Archosauria) from the Late Triassic of North America. Journal of Vertebrate Paleontology 20 (4): 633-636. Online pdf

wiki/Erpetosuchus
wiki/Terrestrisuchus
wiki/Litargosuchus
wiki/Parringtonia
wiki/Tarjadia

wiki/Erpetosuchidae

Enigma archosauriforms pt. 2/3: Tarjadia and Parringtonia

Until recently
all we knew of Parringtonia and Tarjadia were bone scraps of erpetosuchid affinity. Now with more complete skeletons (Figs. 1, 2) the large reptile tree (LRT, 1205 taxa, Fig. 4) confirms that nesting.

FIgure 1. The latest data on Parringtonia, a taxon nesting with Tarjadia and Erpetosuchus in the LRT. Parringtonia and Tarjadia are quadrupeds descendants from bipedal Terrestrisuchus and other bipedal ancestors.

FIgure 1. The latest data on Parringtonia, a taxon nesting with Tarjadia and Erpetosuchus in the LRT. Parringtonia and Tarjadia are quadrupeds descendants from bipedal Terrestrisuchus and other bipedal ancestors.

Parringtonia gracilis (Huene 1939; Middle Triassic) is an erpetosuchid crocodylomorph that had regained its rauisuchid size, gait and proportions. The forward curve of the scapula and teeth restricted to the anterior maxilla allies these erpetosuchids. Recent finds (Nesbitt and Butler 2012) have filled out the rest of the skeleton.

Tarjadia ruthae (Arcucci et al. 1998; Ezcurra et al. 2017; Middle Triassic) has an overall similar build and size with a taller cranium, larger antorbital fenestra, and an indented posterior maxilla (taken to extreme in Erpetosuchus, Fig. 3). So finally we have a clue as to how that very unusual trait originated.

According to Wikipedia,
“Prior to 2017, most studies placed Tarjadia outside Archosauria as a member of Doswelliidae. The 2017 specimens instead show that it belonged to the Erpetosuchidae.”

Figure 2. Tarjadia, another former erpetosuchid, with a skull especially similar in dorsal view. Despite this, Tarjadia nests with Parringtonia and Lewisuchus in the LRT.

Figure 2. Tarjadia, another former erpetosuchid, with a skull especially similar in dorsal view. Despite this, Tarjadia nests with Parringtonia and Lewisuchus in the LRT.

Traditional cladograms
nest Tarjadia and Parringtonia with Erpetosuchus (Fig. 3). So does the LRT (Fig. 4).

Erpetosuchus granti (Newton 1894) Late Carnian, Late Triassic, ~60 cm in length. Only the front half of Erpetosuchus is known. Distinct from Tarjadia, the ventral rims of the maxillae and jugals of Erpetosuchus expanded medially to produce wide flat plates that crowd the teeth, the pterygoid, palatine and ectoptergyoid together in the middle. (Did it have cheeks? And to what purpose?) Highly derived Erpetosuchus was much, much smaller overall.

Like Tarjadia teeth erupted only in the anterior jaws. The orbits opened dorsally. The upper temporal fenestrae were wider than long.

What we know of Erpetosuchus, a basal crocodylomorph.

Figure 3. What we know of Erpetosuchus, a basal crocodylomorph, most distinctive in palatal view. Not sure if this taxon had elongate proximal carpals. Note the scale bar. Erpetosuchus is much smaller than Parringtonia and Tarjadia.

These three taxa
and their interrelationships are not controversial.

Tomorrow we’ll look at the LRT origin of this clade
(Fig. 4) and the other branch that includes bipedal crocodylomorphs, along with a conflict in the tree topology with regard to Erpetosuchus itself. All that will come as a surprise to many.

Figure 4. Cladogram of basal archosaurs and kin. Yellow taxa are traditional members of the Erpetosuchidae, not confirmed as monophyletic here.

Figure 4. Cladogram of basal archosaurs and kin. Yellow taxa are traditional members of the Erpetosuchidae, not confirmed as monophyletic here.

Wikipedia reports:
“The position of Erpetosuchidae within Archosauria was uncertain. Erpetosuchidae formed a polytomy or unresolved evolutionary relationship with several other archosaur groups, including AvemetatarsaliaOrnithosuchidaeAetosauria and RevueltosaurusTicinosuchus and ParacrocodylomorphaGracilisuchus, and Turfanosuchus. The removal of Gracilisuchus and Turfanosuchus from the analysis resulted in Erpetosuchidae nesting within the clade Suchia as the sister-taxon of Aetosauria plus Revueltosaurus clade, but not as a sister taxon of Crocodylomorpha as had previously been proposed.”

The LRT nails down the placement of the Erpetosuchidae.
But you have to include the listed taxa to get this result. Excluding taxa always reduces confidence in results because you run the risk of omitting key relevant taxa.

The whole point of this blog
and ReptileEvolution.com is to gently encourage workers not to omit relevant taxa.

References
Arcucci A and Marsicano CA 1998. A distinctive new archosaur from the Middle Triassic (Los Chañares Formation) of Argentina. Journal of Vertebrate Paleontology. 18 (1): 228–232.
von Huene F 1939. Ein kleiner Pseudosuchier und ein Saurischier aus den ostafrikanischen Mandaschichten. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, Beilage-Band, Abteilung B. 81 (1): 61–69.
Nesbitt SJ. et al. 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464(7285):95-8 .
Nesbitt SJ and Butler RJ 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine: 1. doi:10.1017/S0016756812000362
Nesbitt SJ, Stocker MR, Parke WGr, Wood TA, Sidor CA and Angielczy KD 2018. The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosaur: Pseudosuchia) Journal of Vertebrate Paleontology 37, Memoir 17: Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia.

wiki/Tarjadia
wiki/Parringtonia

Enigma archosauriforms pt. 1/3: Pagosvenator

Lacerda et al. 2018
bring us a new large archosauriform, Pagosvenator (Figs. 1, 2), originally considered a member of the Erpetosuchidade (we’ll look more deeply at this clade in the next few days).

By contrast
In the large reptile tree (LRT, 1205 taxa, Fig. 5), Pagosvenator, nests with Decuriasuchus (Fig. 3), far from Erpetosuchus.

Taxon exclusion
I could not find LRT sisters to Erpetosuchus (Litargosuchus and Terrestrisuchus) in the Lacerda et al. paper. Decuriasuchus was mentioned, but I don’t see it in the cladogram (Fig. 4). So, perhaps taxon exclusion on both ends is part of the Lacerda et al. problem.

FIgure 1. Pagosvenator skull in dorsal view.

Figure 1. Pagosvenator skull in dorsal view.

Lacerda et al. acknowledge
the low support given to the nesting of several archosauriform taxa, but do not realize that taxon exclusion is a likely issue, resolved online for the last seven years by the LRT. Folks, you don’t have to use it, but it’s a good idea to include the sister taxa the LRT recovers, just to cover your bases. That’s what it is here for…a second opinion/analysis.

Figure 2. Pagosvenator skull in lateral view and reconstructed. The unknown bone in the mandible is a fragment of the jugal.

Figure 2. Pagosvenator skull in lateral view and reconstructed. The upper unknown bone in the mandible appears to be a fragment of the jugal.

Lacerda et al. considered their find to be
the first occurrence of a member of the Erpetosuchidae in South America.

By contrast, the LRT
nests Pagosvenator with another large, Middle Triassic archosauriform from southern Brazil, Decuriasuchus (Fig. 3). So, the LRT sisters were coeval competitors of similar size and sharing a long list of traits.

Once again, the Vancleavea problem
Lacerda et al. also add a taxon that should not belong here, Vancleavea, because it nests with thalattosaurs, not archosauriforms.

Figure 4. Decuriasuchus, a sister to Pagosvenator in the LRT

Figure 3. Decuriasuchus, a sister to Pagosvenator in the LRT

Unfortunately 
The cladograms used by Lacerda et al. are inadequate due to taxon exclusion. Too few generic taxa. Too many suprageneric taxa.

Figure 3. Cladograms produced by Lacerda et al. 2018.

Figure 4. Cladograms produced by Lacerda et al. 2018. Compare to figure 5. Red asterisk indicates multiple possible nesting sites for Pagovenator. Where is Decuriasuchus and dozens of other taxa? And why is Vancleavea here? Taxon exclusion is a problem the LRT can readily solve.

Figure 5. Subset of the LRT, focusing on basal archosaurs and kin. Yellow taxa are traditional members of the Erpetosuchidae, not confirmed as monophyletic here. Compare to figure 4 from Lacerda et al.

Figure 5. Subset of the LRT, focusing on basal archosaurs and kin. Yellow taxa are traditional members of the Erpetosuchidae, not confirmed as monophyletic here. Compare to figure 4 from Lacerda et al.

Dyoplax was once considered an erpetosuchid.
Earlier the LRT (Fig. 1) nested Dyoplax with the swimming crocodile, Teleosaurus. Wikipedia reports, “Maisch, Matzke and Rathgeber (2013) questioned the placement of Dyoplax within Crocodylomorpha, and claimed that it shared important cranial and postcranial features with Erpetosuchus; the authors tentatively reassigned Dyoplax to Erpetosuchidae.” Seems no one wants to include Erpetosuchidae within the Crocodylomorpha. More taxa clarify this problem.

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Figure 6. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Let’s note
that the basal rauisuchian, Vjushkovia (Fig. 7), is the outgroup for Decuriasuchus and the Poposaurs + Archosaurs.

Figure 7. Vjushkovia, Decuriasuchus and Pagosvenator to scale. The basalmost Vjushkovia is the outgroup for the other two taxa in the LRT.

Figure 7. Vjushkovia, Decuriasuchus and Pagosvenator to scale. The basalmost Vjushkovia is the outgroup for the other two taxa in the LRT.

More erpetosuchids
will be presented over the next few days.

References
França MAG, Ferigolo J and Langer MC 2011. Associated skeletons of a new middle Triassic “Rauisuchia” from Brazil. Naturwissenschaften.
DOI 10.1007/s00114-011-0782-3
Lacerda, MB, de França and Schultz CL 2018.
A new erpetosuchid (Pseudosuchia, Archosauria) from the Middle–Late Triassic of Southern Brazil. Zoological Journal of the Linnean Society, zly008. https://doi.org/10.1093/zoolinnean/zly008
Maisch MW;  Matzke AT; Rathgeber T 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. 267 (3): 353–362.

wiki/Dyoplax
wiki/Decuriasuchus
wiki/Pagosvenator (has not been posted yet)

What is Dyoplax?

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Dyoplax arenaceus (Fraas 1867, Lucas, Wild and Hunt 1998) is a unique Late Triassic crocodylomorph, one of the three original crocodylomorphs in the 19th century along with two aetosaurs.

No bones are present.
Like Cosesaurus it is a natural cast mold. Fraas thought it had the head of a lizard, but the armor of a gavial. Lucas et al. nested it as the oldest sphenosuchian crocodylomorph. Maish et al. nested it with Erpetosuchus.

Here
Dyoplax nests as a basal metriorhynchid, those Jurassic sea crocodiles with flippers for fore limbs and a curved fish-like tail (Fig. 2), which was probably too early to be present. Unfortunately the tail tip and limb tips are missing from the fossil (Fig. 1)

The fossil appears to have no arch of bones separating the upper and lateral temporal fenestrae, but the intervening squamosal appears to be flipped and displaced near the neck ribs. (Black arrow in fig. 1)

Figure 2. Several Jurassic sea crocs, apparently derived from Late Triassic Dyoplax.

Figure 2. Several Jurassic sea crocs, apparently derived from Late Triassic Dyoplax.

Boy, it’s been awhile
since I posted anything. Feels good to be back… but for how long?

References
Fraas O 1867. Dyoplax arenaceus, ein neuer Stuttgarter Keuper-Saurier. Jh. Verein vaterländ. Naturk. Württemberg 23:108-112; Stuttgart.
Lucas SG, Wild R, Hunt AP 1998. Dyoplax O. Fraas, a Triassic sphenosuchian from Germany. Stuttgarter Beiträge zur Naturkunde, B. 263: 1–13.
Maisch MW;  Matzke AT; Rathgeber T 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. 267 (3): 353–362.

 

The joy of finding mistakes: fewer stem dinosaurs

Finding mistakes is what I hope to do every day
in my own work, as well as that of others. Each time that happens, the data set improves. Lumping and splitting improves. The hypothetical topology of the large reptile tree (LRT, 1036 taxa) gets closer to echoing the topology of Nature itself. Science is a process of winnowing through the data and finding earlier mistakes.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

Today
I discovered some scoring errors among former ‘stem dinosaurs’ that turned them into basal crocodylomorphs. That’s a small shift and it involved turning some ‘absent’ scores in pedal digit 5 to ‘unknown’. It’s noteworthy that some related taxa have two tiny phalanges on pedal digit 5. A related taxon, Gracilisuchu, was illustrated by Romer (1972, Fig. 3) as a combination or chimaera of separate specimens, something I just today realized and rescored. One of those specimens is the so-called Tucuman specimen (PVL 4597, Fig 1), which nests apart from the Gracilisuchus holotype (Fig. 2) in the LRT.

Figure 1. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT.

Figure 2. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT. That fibula flange turns out to be another important trait. 

The corrected results
resolve the long proximal carpal issue in crocodylomorphs very neatly. Now, as in traditional thinking, that trait is restricted to only the crocodylomorphs and it gives us a basalmost taxon with the trait, Junggarsuchus. You might think, and it would be reasonable to do so, that phylogenetic bracketing permitted the addition of a long carpus and long coracoids with more confidence to taxa that don’t preserve this, like Gracilisuchus and Saltopus. But another related basal crocodylomorph, Scleromochlus, has small round coracoids, evidently a reversal. The carpal length is not clearly documented in Scleromochlus (Fig. 4).

Gracilisuchus

Figure 3. A basal archosaur with a very similar nasal bone, Gracilisuchus. Note pedal digit 5 here. This is how Romer 1972 illustrated it. The actual data is shown in figure 2, the Tucuman specimen, PVL 4597. The coracoid is not known in the holotype. 

Despite the short round coracoids of Scleromochlu
and its apparently short carpals, enough traits remain to nest it as a basal crocodylomorph, following the rules of maximum parsimony.

Figure 1. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. The size of the Scleromochlus hand makes it the last possible sister to pterosaurs, famous for their very large hands.

Figure 4. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. Large carpals do not appear to be present and the coracoids are not elongated. 

On a more personal note
I found out my art and a short bio were included in a paleoart website:
http://paleoartistry.webs.com while looking for information on friend and paleoartist, Mark Hallett, (wikipage here) whose website is down and I worried about his health. No worries. Mark just let his website lapse.

The author of the paleoartistry page
had both kind words and controversy for me:
“After David Peters’ excellent paintings in Giants, and A Gallery of Dinosaurs and Other Early Reptiles, as well as his own calendar, it seemed he was on his way to becoming one of the most reliable paleoartists of the 1990s, if not of all time. However, very controversial theories on reconstructing pterosaurs led to some harsh critiques obscuring Peters’ artistic brilliance.” 

That’s okay.
“Very controversial” does not mean completely bonkers (or am I reading too little into this?). It just means it inspires a lot of chatter. Or… it could mean that the author of the post follows the invalidated observations of Elgin, Hone and Frey 2010, which are the traditional views (Unwin and Bakhurina 1994), still used in David Attenborough films. If so, that would be a shame. Science is usually black and white – is or isn’t, because you can observe and test (Fig. 5) and all tests, if done the same, should turn out the same.

And you don’t toss out data
that doesn’t agree with your preconception, like Elgin, Hone and Frey did. In reality, my “very controversial reconstructions” remain the only ones built with DGS, not freehand guesswork or crude cartoonish tracings (as in Elgin, Hone and Frey 2010). The membranes (brachiopatagia and uropatagia) were documented in precise detail in Peters 2002, 2009 and here online.

Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

Figure 5. Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Romer AS 1972. 
The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

wiki/Gracilisuchus
paleoartistry.webs.com/1980s.htm

Saltopus preserves early archosaur skin and scales

Basal Crocodylomorpha

Figure 1. Basal Crocodylomorpha, including Gracilisuchus, Saltopus, Scleromochlus and Terrestrisuchus

The basal archosaur
(crocs + dinos) Saltopus (von Huene 1910; Late Triassic; ~210 mya, ±60 cm long; Figs. 1–3) poorly preserves bones, but also preserves some scaly skin.

Figure 2. Saltopus skin and scales surrounding the right pelvis.

Figure 2. Saltopus skin and scales surrounding the right pelvis. Not all bones nor all scales are traced here. Benton and Walker 2011 reported no evidence for osteoderms. The bones are hard to delineate and segregate from scales because here they are covered with fossilized desiccated skin. Photo from Benton and Walker 2011 who trace the femoral head extending beneath the pelvis. 

Saltopus nests well within
the Crocodylomorpha and, along with Scleromochlus (Fig. 1), present examples of basal archosaur skin and scales. Even more basal, Gracilisuchus (Fig. 1) had dorsal scutes derived from ancestors going back to the Early Triassic Euparkeria.

Figure 2. Saltopus pelvis latex peel from Benton and Walker 2011. They found two large sacrals. Using DGS I found four sacrals, the same length as the dorsals and causals. Sister taxa have four sacrals.

Figure 2. Saltopus pelvis latex peel from Benton and Walker 2011. They found two large sacrals. Using DGS I found four sacrals, the same length as the dorsals and causals. Sister taxa have four sacrals.

Gracilisuchus and basal dinosaurs
had only two sacral vertebrae, but basal bipedal crocs, like Scleromochlus, double that number. Benton and Walker 2011 traced two sacrals in a latex cast of the sacral area, but each sacral was twice as long as proximal dorsals and causals. Here four sacrals are tentatively identified in the latex peel, all about as long as proximal non-sacral vertebrae.

Dinosaur skin
can be scaly, or naked with feathers, or a combination of the two. Dinosaur scales may be different than croc or lizard scales in that at least some dinosaur scales, like those on the metatarsus of theropods appear to be derived from former feathers.

References
Benton MJ and Walker AD 2011. Saltopus, a dinosauriform from the Upper Triassic of Scotland. Earth and Environmental Science Transactions of the Royal Society of Edinburgh: 101 (Special Issue 3-4):285-299. DOI:10.1017/S1755691011020081
von Huene FR 1910. Ein primitiver Dinosaurier aus der mittleren Trias von Elgin. Geol. Pal. Abh. n. s., 8:315-322.

wiki/Saltopus