Hemiprotosuchus: closer to Aetosaurus than Protosuchus

Not much written about this genus
According to Wikipedia, “Hemiprotosuchus is an extinct genus of protosuchid from the Late Triassic (Norian stage) Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina, South America.” 

Figure 1. Hemiprotosuchus leali skull from Desojo and Ezcurra, nests with Decuriasuchus in the LRT. The variation within this clade is increased with this nesting.

The specimen
(Fig. 1, image from Desojo and Ezcurra 2016) seems to be preserved as a half skull, nearly complete. Bonaparte 1969 first considered this a protosuchid like Protosuchus (Fig. 2), likely due to its low triangular rostrum and high temporal region.

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

After testing
in the large reptile tree (LRT, 1594 taxa) Hemiprotosuchus (PVL 3829, Bonaparte 1969; Norian, Late Triassic) nested between Ticinosuchus (Fig. 3) and aetosaurs, like Stagonolepis and Aetosaurus (Fig. 3).  That’s a long way from Protosuchus in the LRT.

In 1969 no one knew
that Ticinosuchus was basal to aetosaurs. The LRT recovered that relationship here in 2011.

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

Others (e.g. Nesbitt 2011 and works based on that cladogram)
considered Revueltosaurus (Fig. 3) a basal aetosaur. The LRT nests Revueltosaurus closer to the genesis of the Euarchosauriformes (between Euparkeria and Erythrosuchus among lesser known taxa).

Desojo and Ezcurra 2016
accepted the protorosuchian affinities of Hemiprotosuchus without further comment.

---

References
Bonaparte JF 1969. Dos nuevas ‘faunas’ de reptiles triasicos de Argentina. Gondwana Stratigraphy (IUGS Symposium, Buenos Aires)2:283–306.
Desojo JB and Ezcurra MD 2016. Triassic pseudosuchian archosaurs of South America. Historia Evolutiva y Paleobiogeográfica de los Vertebratos de América del Sur. XXX Jornados Argentinas de Paleontología de Vertebrados. Contribuciones del MACN No. 6: 57–66.

wiki/Hemiprotosuchus

Not Arizonasaurus, but Postosuchus, made the giant Isochirotherium tracks

A recent paper by Diedrich (2015) purported to match the Arizonasaurus to giant Isochirotherium tracks from the Middle Triassic of Germany (Fig. 1).

The problem is,
no manus or pes are known for Arizonasaurus. Furthermore, all related taxa in the large reptile tree have digit 3 the longest, and all digits are elongate. The giant Isochirotherium tracks indicate that both digits 2 and 3 are the longest, and they are short. So matching candidates have to be found elsewhere, not close to Arizonoasaurus (although the size and time are right!).

Among the 504 taxa in the large reptile tree that are possible candidates with digits 2 and 3 the longest are Erythrosuchus (Fig. 1), Shansisuchus, Lotosaurus and the Postosuchus alisonae (Peyer 2008, Fig. 1). It turns out that only the latter is the best match when scaled up to the size of P. kirkpatrchicki (Chatterjee 1985, Fig. 1).

Figure 1. Giant Isochirotherium tracks matched to Postosuchus alisonae scaled up to the size of P. kirkpatrcki. Click to enlarge. This taxon was not considered originally because it is Late Triassic and the tracks are Middle Triassic.

Postosuchus was not mentioned in the text
because Diedrich (recent email) knew Postosuchus was Late Triassic, not Middle Triassic. He did not accept the idea that between the origin, radiation and extinction of Postosuchus there might have been a Middle Triassic relative.

Diedrich also saw the small manus tracks and assumed they were produced by a large poposaurid. Unfortunately, Arizonasaurus does not nest with poposaurids either. And poposaurids, other than Lotosaurus, do not match the track morphology.

It would have been helpful,
I suppose, to do what I did and make a list of possible candidates from a large list, AND THEN delete the possible candidates one by one as bad matches. Other than that phylogenetic bracketing mismatch, Diedrich does good work with excellent graphics. It took a leap of faith, I suppose to match tracks to a taxon for which no manus or foot is known.

C. Diedrich writes:
“Watch my ARTE docu – there you see Arizonasaurus (Ticinosuchus and Macrocnemus) walking in my point of view combining trak/sleketal records”:http://www.youtube.com/watch?v=b9GcVmb6OtE

References
Chatterjee S 1985. Postosuchus, a new Thecodontian reptile from the Triassic of Texas and the origin of Tyrannosaurs. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 309 (1139): 395–460. doi:10.1098/rstb.1985.0092.
Diedrich C 2015. Isochirotherium trackways, their possible trackmakers (?Arizonasaurus): intercontinental giant archosaur migrations in the Middle Triassic tsunami-influenced carbonate intertidal mud flats of the European Germanic Basin  Carbonates and Evaporites  DOI 10.1007/s13146-014-0228-z
Novak SE 2004. A new specimen of Postosuchus from the Late Triassic Coelophysis Quarry, siltstone member, Chinle Formation, Ghost Ranch, New Mexico. M.S. thesis, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Peyer K Carter, JG, Sues H-D, Novak SE, and Olsen PE 2008. A new Suchian Archosaur from the Upper Triassic of North Carolina. Journal of Vertebrate Paleontology 28 (2): 363–381. doi:10.1671/0272-4634(2008)28[363:ANSAFT]2.0.CO;2.

A closer look at Sikannisuchus huskyi

Earlier we looked at the skull roof of Sikannisuchus. Unfortunately, I ignored those long mandible bits and pieces. These give us more clues to restore the missing parts in lateral view (Fig. 1).

Sikannisuhus huskyi restored on must a view bits and pieces. Nesting with Postosuchus provides clues to the shapes of the missing parts. That’s a nice long skull. Must have been a BIG reptile.

If I made any errors, or the clues point in another direction, let me know.

References
Nicholls EL, Brinkman DB and Wu K-C 1998. A new archosaur from the Upper Triassic
Pardonet Formation of British Columbia. Canadian Journal of Earth Science 35: 1134–1142.

Arizonasaurus vs Spinosaurus

Two unrelated reptiles
evolved similar morphologies, Arizonasaurus and Spinosaurus (Fig. 1), a long rostrum filled with sharp teeth, a bipedal configuration and enormous neural spine arising from the dorsal vertebrae. One was a giant. The other about waist high. Seen here together for the first time…

Figure 1. Spinosaurus and Arizonsaurus, together for the first time. The similarities are obvious and intriguing. Spinosaurus courtesy of Scott Hartmann.

Spinosaurus is a famous giant theropod dinosaur. Arizonasaurus is none of these things. It’s a member of a clade that has no name, but arose from basal rauisuchids, like Venjukovia. It was a sister to Ticinosuchus + Aetosaurs and Yarasuchus + Qianosuchus, none of which have much of a sail back. I thought comparing these two might provide clues to their convergent looks.

Arizonasaurus comes from the Middle Triassic Moenkoepi Formation, which included fresh water and a diverse fauna. Earlier we looked at the possibility that this predator was bipedal, based on the very small pectoral girdle and very deep (for its time) pelvic girdle, almost like that of T-rex, but more gracile. Relatives include fish eaters, like long-necked Yarasuchus and plant eaters, like aetosaurs. So this is already a diverse clade that no doubt will provide many surprising morphologies in the future. Originally described as a prestosuchid rauisuchian, Brusatte et al. (2010) nested it with poposaurs. In the large reptile tree poposaurs nest a little closer to dinosaurs and basal crocs.

Spinosaurus comes from the Middle Cretaceous of northern Africa, which, at the time included tidal flats, mangrove forests and several other giant theropods. Only a few other dinosaurs had such long neural spines. The question is, where they more like sails, and aid in thermoregulation? Or did they support a buffalo-like hump of fat? Spinosaur relatives, all smaller, did not sport much of a sail back. So whatever its utility was, it was unique.

Sail backs seem to spring up occasionally and quickly around the reptile family tree. They never seem to last.

Moving on
to those long jaws, Spinosaurus was considered a quick-strike artist, feeding on everything from fish to small dinosaurs, but with that size it could have taken on any prey. No such claims have been made for Arizonasaurus, perhaps because not much of the skull is known. But the teeth were sharp

My take
I have no expertise and no stake in the hump vs. sail argument. Since these sails seem to come and go rather quickly, my opinion is they are literally a flash in the pan, thus they have no real utility and are only for show… secondary sexual traits. Popular one day, not so popular the next. The blessing probably becomes a curse over time, as the sail gets bigger, so the trait and the animal disappears. The neural spines are broad because they have “roots” that are broad, unlike Dimetrodon and like Sphenacodon.

References
Bailey JB 1997. Neural spine elongation in dinosaurs: sailbacks or buffalo-backs?. Journal of Paleontology 71 (6): 1124–1146.
Butler RJ, Brusatte SL, Reich M, Nesbitt SJ, Schoch RR, et al. 2011. The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation. PLoS ONE 6(10): e25693. doi:10.1371/journal.pone.0025693 Plos One paper
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence. Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
Nesbitt SJ, Liu J and Li C 2010. A sail-backed suchian from the Heshanggou Formation (Early Triassic: Olenekian) of China. Transactions of the Royal Society of Edinburgh 101 (Special Issue 3-4):271-284.
Welles SP 1947 Vertebrates from the Upper Moenkopi Formation of the Northern Arizona. Univ. California Publ. Geol. Sci. 27, 241–294.
Wu X-C 1981. The discovery of a new thecodont from north east Shanxi. Vertebrata PalAsiatica 19: 122–132.

wiki/Arizonasaurus
wiki/Ctenosauriscus

Revueltosaurus: closer to Aetosaurus? or to Fugusuchus?

This post was updated December 8, 2014 with a new nesting of Revueltosaurus with Fugusuchus as a basal erythrosuchid. 

Yesterday we saw a higher resolution Revueltosaurus skull in lateral view and we noted a disagreement in the phylogenetic nesting of this Late Triassic oddball.

According to Nesbitt (2011)…
Nesbitt (2011) nested the odd herbivorous Triassic archosauriform, Revueltosaurus, at the base of the aetosaurs, including Aetosaurus and Stagonolepis. Outgroups include an unresolved clade including Gracilisuchus, Turfanosuchus and Ticinosuchus. Outgroups to this clade include Riojasuchus and Ornithosuchus (= Ornithosuchidae) at the base of the “Pseudosuchia“. Wiki follows Nesbitt (2011).

According to Parker (2014?)…
William Parker, the discoverer of the twelve-specimen nest of Revueltosaurus skeletons, will soon publish a large monograph on this genus. His analysis will also nest Revueltosaurus with aetosaurs. He’s very sure of that.

Figure 1. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

According to the large reptile tree…
On the other hand, the large reptile tree does not recover the Nesbitt tree topology, but finds Revueltosaurus nests with Fugusuchus (Fig. 1) at the base of the Erythrosuchidae. To move Revueltosaurus to the Aetosauridae requires an additional 35 steps. t.

Like Aetosaurs:
Revueltosaurus is a heavily armored quadruped and a plant eater (judging by its teeth). I’m told by Parker the following traits are identical in Revueltosaurus and aetosaurs: scapula/coracoid, humerus, squamosal and armor design. You can see (Fig. 1) that despite being twice the size, Revueltosaurus has more gracile girdles and limbs and larger hands and feet than Aetosaurus. And the skull has a distinctly different shape in nearly all regards, including the squamosal. Even so…

An herbivorous rauisuchid, with several aetosaur and turtle-like traits.
On Revueltosaurus, the naris is rather unique. The lateral processes of the premaxilla have become more robust, reducing the size of the naris and moving them to an anterior position.  Revueltosaurus shares these traits with Fugusuchus.

Figure 2. Revueltosaurus pelves compared to Aetosaurus and Postosuchus. Red arrows point to limit of femoral head. Blue arrows point to acetabular shelf that roofs over the femur in rauisuchids. Revueltosaurus is a small slow quadrupedal plant eater, so it doesn’t have the long booted pelvis of Postosuchus. But note the similarity of the broad ischium to Aetosaurus!  Wm. Parker tells me, “It’s the plesiomorphic archosauriform condition with the very short anterior process. Lacks the deep supracetabular buttress found in rauisuchids. It actually looks like a juvenile aetosaur and it is difficult to tell them apart.” Schoch reports the aetosaur oblique posterior ridge is unlike the supraacetabular ‘boss’ of rauisuchids.

The pelvis should settle the argument
But it doesn’t. The pelvis of Revueltosaurus appears to bear a acetabular boss beneath which the femur articulates and supports. In aetosaurs the pelvis has a simpler shape without the boss. In aetosaurs the pelvis is wider at the top, which provides a broad platform for the armor, and angles inward ventrally. We don’t have a pelvis and hind limb for Fugusuchus, but Euparkeria is not far off. So is Gargainia. Both have similar elements.Here again, the different nesting sites appear to be based on employing macro-traits or micro-traits. This is a problem I have no solution for at present.

Figure 2. Revueltosaurus

 

References
Hunt AP 1989. A new ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. In Lucas, S. G. and A. P. Hunt (Eds.), Dawn of the age of dinosaurs in the American Southwest 355–358.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Parker WG., et al. 2005. The Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.

wiki/Revueltosaurus

Revueltosaurus in higher resolution

An online photo of Revueltosaurus (Fig. 1) adds details and clarifies problems. There is also a Vimeo video here featuring paleontologist, William Parker, who authors the Chinleana blogsite. He also discovered 11 skeletons of Revueltosaurus from one site with two that are nearly complete or complete. From that data the complete skeleton (Fig. 1) has been recreated.

Figure 1. Revueltosaurus skull from online source (link above) color coded to bone. Above, the aetosaur, Stagonolepis, to which Nesbitt and Parker nest Revueltosaurus. In contrast, the large reptile tree nests Fugusuchus with Revueltosaurus as a derived herbivorous erythrosuchid.

With this data, Nesbitt (2011) nested Revueltosaurus at the base of the Aetosauria with Aetosaurus and Stagonolepis.

In counterpoint,
The large reptile tree, employing a different character list, nested Revueltosaurus with Postosuchus, as a derived, smaller, somewhat turtle-ized rauisuchid.

We’ll look at the pros and cons of both analyses tomorrow.

References
Hunt AP 1989. A new ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. In Lucas, S. G. and A. P. Hunt (Eds.), Dawn of the age of dinosaurs in the American Southwest 355–358.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Parker WG., et al. 2005. The Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.

wiki/Revueltosaurus

Luperosuchus: an erythrosuchid, not a rauisuchian

Luperosuchus fractus (Romer 1972, PULR 04) was considered a indistinct pseudosuchian originally and later a rauisuchian by Desojo and Arcucci (2009). The large reptile tree recovers it as an erythrosuchid and a sister to Shansisuchus, which had an even larger subnarial fenestra. Earlier we looked at the two Shansisuchus specimens, noting that the referred specimen was much larger than the holotype with a distinct morphology, more like Luperosuchus.

Figure 1. Luperosuchus restored based on Romer 1971. Above: original drawing by Romer. Below tracing based on photo in Romer 1971, specimen PULR 04. Extension of the qj and a deeper max gives it more of a erythrosuchid look. At right is referred specimen PULR 057. Although related, the referred specimen strikes me as generically different with the low placement of the naris and large postorbital. Analysis on PULR 057 has not been done.

The reconstruction by Desojo and Arcucci (2009, Fig. 1, above) assumes a short quadratojugal, but a longer qj (Fig. 1, below) matches sister taxa.

This one is probably a rauisuchid
Another much smaller specimen (PULR 057, Fig. 1) was referred to Luperosuchus. That seems doubtful based on the lower placement of the naris, the straighter rostral profile, the larger antorbital fenestra, the deeper pmx/mx notch and the more robust postorbital. These traits appear to lead to Ticinosuchus and the aetosaurs as other archosauriformes retain a high naris. A second possibility leads toward the euparkeriid Osmolskina. A phylogenetic analysis was not attempted due to the small number of traits shown.

References
Desojo JB and Arcucci AB 2009. New material of Luperosuchus fractus (Archosauria: Crurotarsi) from the Middle Triassic of Argentina: the earliest known South American ‘Rauisuchian’. Journal of Vertebrate Paleontology 29(4): 1311-1315. 
Romer AS 1971. The Chañares (Argentina) Triassic reptile fauna. VIII. A fragmentary skull of a large thecodont, Luperosuchus fractus. Breviora 373:1-8.

Short note: ReptileEvolution.com has just passed a million hits for this year. Between 4.2 and 5.7 thousand unique visitors access the site every month.

What is Asperoris?

A recent online paper by Nesbitt et al. 2013 introduces us to a new Middle Triassic East African archosauriform, Asperoris mnyama (NHMUK PV R36615), known from several 3D skull pieces (Fig. 1).

Figure 1. Asperoris skull reconstruction. Turns out it’s just an ordinary rauisuchid linking Vjushkovia to more derived forms. Tooth length is pure guesswork.

Nesbitt et al. was unable to resolve what Asperoris was (Fig. 2). So they considered it a “non-archosaurian archosauriform” (incerta sedis). Unfortunately they included rauisuchids within the Archosauria in their analysis AND they included several unrelated taxa: a lepidosauriform (Mesosuchus), a thalattosaur (Vancleavea) and two pararchosauriform supragenera (Proterochampsidae and Phytosauria). That didn’t leave too many related taxa to compare Asperoris to. And they missed the most obvious candidates, like Vjushkovia (Fig. 3). That’s why we turn to the large reptile tree (Fig. 2, subset here) to find out where Asperoris might nest.

Figure 2. The confused nesting of Asperoris according to Nesbitt et al. 2013 (above) and the exact nesting according to the large reptile tree (below) as as sister to Vjushkovia.

The large reptile tree data analysis started with a reconstruction of Asperoris (Fig.1), which enabled the employment of several traits not readily apparent from the separated bones. The results nested Asperoris within the Rauisuchidae as the sister to Vjushkovia,  a taxon not included in the Nesbitt (2011) study on archosaurs.

The Nesbitt et al. 21013 definition of Archosauria is not confirmed here.
Nesbitt et al. report, “Archosauria, the crown clade that includes living birds and crocodilians as well as extinct dinosaurs, pterosaurs and pseudosuchians (stem-crocodilians), is one of the most successful evolutionary radiations in the history of vertebrate life on land.” In the large reptile tree, Archosauria includes just crocs and dinos (including birds). Pterosaurs nest with tritosaur lizards. Pseudosuchians, it turns out, are diphyletic with parasuchians and proterochampsids nesting with choristoderes, on a separate branch from the rest of the traditional archosauriforms.

Not far from Vjushkovia
Asperoris shared many skull traits with Vjushkovia and was about the same size. Like Vjushkovia, Asperoris also lacked an antorbital fossa on the maxilla. According to Nesbitt et al. “Asperoris mnyama differs from all known archosauriforms in having highly sculptured cranial elements including the premaxilla, maxilla, nasal, prefrontal, frontal, postfrontal, and parietal, and in having a highly sculptured, dorsoventrally deep orbital margin of the frontal.” This may be a distinct trait indeed.

Figure 3. Vjushkovia had 3 premaxillary teeth and a descending jugal, but otherwise would have been similar to Asperoris in shape and size.

So no great shakes. 
Asperoris was about the size of Vjushkovia and Batrachotomus, so smaller than some rauisuchids. It’s not a key taxon providing new insight into relationships.

Sadly,
having access to data that showed pterosaurs and Vancleavea should not be included in archosauriform studies was not followed by any testing of these oddly nested taxa. Rather Nesbitt et al. (2013) held on to their old traditions — which is a major problem with their study.

Once again, I have not seen the original material (nothing here changes in interpretation anyway), but I do have a larger gamut study from which more accurate and confident nestings can be made. This is available to anyone who wishes to use it. Moreover, the taxonomic clades that result can provide guidance for future inclusion sets. At least they should be tested.

References
Nesbitt SJ 2011. The early evolution of archosaurs: Relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Nesbitt SJ, Butler RJ, Gower DJ 2013. A New Archosauriform (Reptilia: Diapsida) from the Manda Beds (Middle Triassic) of Southwestern Tanzania. PLoS ONE 8(9): e72753. doi:10.1371/journal.pone.0072753

NHMUK, The Natural History Museum, London, United Kingdom;

The Sailback Arizonasaurus – a Good Bipedal Candidate

Figure 1. Arizonasaurus configured as a biped. The depth of the pubis suggests a similar length for the femur and the tibia follows. The gracile pectoral girdle suggests a gracile forelimb, perhaps smaller than shown here. The long deep tail is based on the related Yarasuchus. Looks a little like Spinosuchus, doesn’t it? And this clade is known for fish-eating.

Like the cheese, Arizonasaurus stands alone. Almost.
Phylogenetic analysis nests what is known about Arizonasaurus with Yarasuchus and Qianosuchus two sail-less ticinosuchians (not poposaurs, as envisioned by Nesbitt 2011).

Another sailback, Lotosaurus does nest with poposaurs, though, but it’s quite different and a herbivore.

Figure 2. Xilousuchus and Yarasuchus compared. Yarasuchus is a sister to Arizonasaurus, but has a much more robust pectoral girdle.

We don’t have any fore limbs or hind limbs for Arizonasaurus,
but we do have its pectoral and pelvic girdles.

The pelvic girdle is very deep, compared to the ancestral Vjushkovia, and sister taxa like Yarasuchus, Qianosuchus and Ticinosuchus. In these taxa the femur extends at least as far as the pubis depth and sometimes a little further. If we add such femora to the reconstruction of Arizonasaurus, it becomes essentially bipedal.

The pectoral girdle is quite small and gracile. It would be odd for massive or elongate forelimbs to be attached to such a small pectoral girdle, so here (Fig.1) an appropriate gracile short forelimb is added.

But wait, that’s not all.
That sail adds leverage and strength to the back bone, helping to hold up the elevated anterior half. Moreover, if we add on the deep tail of the related Yarasuchus, we reconstruct a substantial counterbalance (Fig. 1).

References
Butler RJ, Brusatte SL, Reich M, Nesbitt SJ, Schoch RR, et al. 2011. The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation. PLoS ONE 6(10): e25693. doi:10.1371/journal.pone.0025693 Plos One paper
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence
Sterling J. Nesbitt Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
Nesbitt SJ, Liu J and Li C 2010. A sail-backed suchian from the Heshanggou Formation (Early Triassic: Olenekian) of China. Transactions of the Royal Society of Edinburgh 101 (Special Issue 3-4):271-284.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Welles SP 1947 Vertebrates from the Upper Moenkopi Formation of the Northern Arizona. Univ. California Publ. Geol. Sci. 27, 241–294.
Wu X-C 1981. The discovery of a new thecodont from north east Shanxi. Vertebrata PalAsiatica 19: 122–132.

wiki/Arizonasaurus

Poposaur palates

The palates of poposaurs are poorly known Some have not been described or reconstructed (Fig.1). Others have been wrongly reconstructed or partially reconstructed (Fig. 4). Here (Fig. 1) are two poposaurs, Effigia and Shuvosaurus next to Daemonosaurus (Sues et al. 2011, also largely guessed at from broken pieces) and Thecodontosaurus, which provides more certitude. Most unfortunately, the palate of Lotosaurus has not been described or illustrated despite the presence of several specimens and museum casts. The little question is: On Daemonosaurus, which way do the ectopterygoids go? Long side against the pterygoid, as in rauisuchids? Or short side, as in Effigia and other dinosaurs?

Figure 2. Effigia palate in situ (left) and reconstructed by reassembling colored elements (at right).

On rauisuchians, as in ornithosuchians (Fig. 2), the ectopterygoid has a larger contact area with the lateral pterygoid and it produces a small “stem” to contact the jugal (as in Saurosuchus) or the maxilla (as in Riojasuchus). If you flip the ectopterygoid of Daemonosaurus, you get the rauisuchian type of ectopterygoid. Left as is (Fig. 1), however, you get the dinosaurian type,  and that is the preferred reconstruction here based on phylogenetic bracketing.

Figure 2. Click to enlarge. Euparkeriid, ornithosuchian, rauisuchian, aetosaurian, and basal archosaur palates. Here are Euparkeria and Osmolskina, both euparkeriids. Ornithosuchus and Riojasuchus are ornithosuchids. Saurosuchus and Postosuchus are both rauisuchians. Stagonolepis is an aetosaur. Pseudhesperosuchus is close to the basal archosaur pattern with a much smaller ectopterygoid and smaller ectopterygoid/pterygoid contact. The original configuration is shown on the right side. A possible alternative is shown on the left. Not sure how it was preserved. I’d like to know if you have this data. If the left is correct in figure 2 (Pseudohesperosuchus), and Shuvosaurus is also correct in figure 1, these suggest that Daemonosaurus is correctly drawn in figure 1.

Figure 4. Silesaurus palate with missing elements restored on the right. Illustration (without color) from Dzik 2003 who illustrated missing elements on the left.

Silesaurus Palate The missing ectopterygoid and palatine were not illustrated for Silesaurus. Given the palates of related taxa (Fig.1), I have added the missing elements on the right here (Fig. 4) to match them. Thus these restorations are guesses that appear to make sense in context. When better data come along, we’ll make improvements.

This has been a first attempt at reconstructing the palates of several poposaurs at once based on similar morphologies in close kin. The palates should remain somewhat similar. If anyone has good data on the palates of other rauisuchians and basal dinosaurs, please forward them on.

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.

Figure 3 is absent from this post now. Apologies. I had it in my files for several years and thought it had been published by now. It had not. 

 

References Bonaparte JF 1969. Dos nuevas “Faunas” de reptiles Triasicos de Argentina: I. Gondwana Symp., IVGS: 283-306.
Borsuk-Bialynicka M and Evans SE 2009. Cranial and mandibular osteology of the Early Triassic archosauriform Osmolskina czatkowicensis from Poland. Palaeontologia Polonica 65, 235–281.
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