SVP abstracts 22: Weigeltisaurus reexamined

Pritchard, Sues, Reisz and Scott 2020
promise to bring us a look at the ‘osteology and phylogenetic affinities of the early gliding reptile Weigeltisaurus jaekeli” (Fig. 1).

Unfortunately,
no phylogenetic analysis, or any hint thereof, is to be found in the abstract.

We looked at Weigeltisaurus earlier
here when the skull (Fig. 1) was described by Bulanov and Sennikov 2015.

Figure 1. Weigeltisaurus skull reconstructed by Bulanov and Sennikov (gray scale), and using DGS techniques (color). They did not attempt to trace the occiput, nor did they understand that the posterior crest is the supratemporal, displaced in situ and that the main portion is a very large squamosal that sweeps up. This skull is nearly identical to that of sister taxa, with the exception of the extended posterior elements, probably for secondary sexual selection. The same cannot be said of the Bulanov and Sennikov reconstruction which is, unfortunately, unique as is.

Figure 1. Weigeltisaurus skull reconstructed by Bulanov and Sennikov (gray scale), and using DGS techniques (color). They did not attempt to trace the occiput, nor did they understand that the posterior crest is the supratemporal, displaced in situ and that the main portion is a very large squamosal that sweeps up. This skull is nearly identical to that of sister taxa, with the exception of the extended posterior elements, probably for secondary sexual selection. The same cannot be said of the Bulanov and Sennikov reconstruction which is, unfortunately, unique as is.

Weigeltisaurus is a relative of Coelurosauravus 
(Fig. 2) and other pseudo-rib gliders. The ribs are dermal in nature, extending from the tips of the dorsal and lumbar ribs, whether few or many.

The Triassic kuehneosaur gliders and their non-gliding precursors.

Figure 2. Click to enlarge. The Triassic kuehneosaur gliders and their non-gliding precursors. Note the icarosaurs are not rib gliders. Their actual ribs are fused to mimic transverse processes as demonstrated around the neck and anterior torso.

From the Pritchard et al. 2020 abstract:
“Weigeltisauridae is a clade of small-bodied Permian diapsids that represent the oldest known vertebrates with skeletal features for gliding. It is characterized by a cranium with a posterior bony casque, prominent horns on the temporal arches, and a series of elongate bony spars projecting from the ventrolateral surface on both sides of the trunk. Definitive specimens are known from upper Permian of Germany, Russia, and Madagascar, but the quality of their preservation previously limited understanding of the skeletal structure and phylogenetic affinities of these reptiles.”

All you have to do is add taxa (= minimize taxon exclusion) and let the software determine where these Permian pseudo-rib gliding lepidosauriforms nest. In the large reptile tree (LRT, 1752+ taxa; subset Fig. 3) these arboreal gliders nest at the base of the lepidosauriformes. (The Diapsida is now limited to just archosauromorphs with a diapsid-skull morphology, by convergence with lepidosauriformes). Only here, in the LRT, among all prior pertinent cladograms, is the clade of pseudo-rib gliders surrounded by arboreal taxa with weigeltosaurs nesting with kuehneosaurs. Usually they nest apart and too often close to marine taxa.

Figure 2. Derived lepidosauriformes. The clade Pseudoribia includes the pseudo-rib gliders

Figure 2. Derived lepidosauriformes. The clade Pseudoribia includes the pseudo-rib gliders

The Pritchard, Sues, Reisz and Scott abstract continues:
“Here, we present a revised account based on a nearly complete skeleton of Weigeltisaurus jaekeli from the Kupferschiefer of central Germany and a revised phylogenetic analysis of early Diapsida and early Sauria.”

That analysis must have been part of the oral presentation. There is no hint of it here. Sauria is an invalid clade. Diaspsida is restricted to the Archosauromorpha in the LRT.

“The specimen preserves all elements of the skeleton, save for the braincase, palate, some dorsal vertebrae, the carpus, and the tarsus. The well-preserved teeth in the maxilla are not conical but leaf-shaped, resembling those in the middle portion of the maxillae of the Russian weigeltisaurid Rautiania. The parietals bear rows of dorsolaterally oriented horns similar to those on the squamosals. The quadrate is a dorsoventrally short element with a tapering dorsal margin that lacks a cephalic condyle. The squamosal appears to cover the quadrate both laterally and posterodorsally. The manual and pedal phalanges are elongate and slender, similar to those of extant arboreal squamates. The unguals have very prominent flexor tubercles. A patagium was supported by elongate, slender bony rods. They are situated superficial to the preserved dorsal ribs and gastralia, corroborating the hypothesis that these structures represent dermal ossifications independent of and greater in number than the bones of the dorsal axial skeleton.”

Excellent description. But that was provided earlier (Bulanov and Sennikov 2015).

Phylogenetic conclusions? 
I guess we’ll have to wait for the paper.


References
Bulanov VV and Sennikov AG 2015. Substantiation of validity of the Late Permian genus Weigeltisaurus Kuhn, 1939 (Reptilia, Weigeltisauridae) Paleontological Journal 49 (10):1101–1111.
Pritchard A, Sues HD, Reisz R and Scott D 2020. Osteology and phylogenetic affinities of the early gliding reptile Weigeltisaurus jaekeli. SVP abstracts.

https://pterosaurheresies.wordpress.com/2011/09/26/icarosaurus-kuehneosaurus-and-the-so-called-rib-gliders/

https://pterosaurheresies.wordpress.com/2015/12/17/weigeltisaurus-skull-reconstructions/

Prior citations
Colbert, Edwin H. (1966). A gliding reptile from the Triassic of New Jersey. American Museum Novitates 2246: 1–23. online pdf
Evans SE 1982. Gliding reptiles of the Late Permian. Zoological Journal of the Linnean Society, 76:97–123.
Evans SE and Haubold H 1987. 
A review of the Upper Permian genera  CoelurosauravusWeigeltisaurus and Gracilisaurus (Reptilia: Diapsida). Zool J Linn Soc, 90:275–303.
Fraser NC, Olsen PE, Dooley AC Jr and Ryan TR 2007. 
A new gliding tetrapod (Diapsida: ?Archosauromorpha) from the Upper Triassic (Carnian) of Virginia. Journal of Vertebrate Paleontology 27 (2): 261–265. doi:10.1671/0272-4634(2007)27[261:ANGTDA]2.0.CO;2.
Frey E, Sues H-D and Munk W 1997. 
Gliding Mechanism in the Late Permian Reptile Coelurosauravus. Science Vol. 275. no. 5305, pp. 1450 – 1452
DOI: 10.1126/science.275.5305.1450
Li P-P, Gao K-Q, Hou L-H and Xu X. 2007. A gliding lizard from the Early Cretaceous of China. PNAS 104(13): 5507-5509. doi: 10.1073/pnas.0609552104 online pdf
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Modesto SP and Reisz RR 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles. SVPCA abstract.
Robinson PL 1962. Gliding lizards from the Upper Keuper of Great Britain. Proceedings of the Geological Society London 1601:137–146.
Stein K, Palmer C, Gill PG and Benton MJ 2008. The aerodynamics of the British Late Triassic Kuehneosauridae. Palaeontology, 51(4): 967-981. DOI: 10.1111/j.1475-4983.2008.00783.x
Piveteau J 1926. Paleontologie de Madagascar, XIII. Amphibiens et reptiles permiens: Annales de Paleontologie, v. 15, p. 53-128.

Where is the rest of Lanthanolania?

It was back in 2011
when the post-crania of Lanthanolania (Fig. 1) was reported in an abstract by Modesto and Reisz. Prior to that, in 2003, only the skull was described by the same authors. Over the last six years the post-crania of Lanthanolania has not been published.

From the 2011 SVPCA abstract:
“The evolutionary history of Diapsida during the Palaeozoic Era is remarkably poor. Following the reclassification of the Early Permian Apsisaurus witteri as a synapsid last year, only a handful of taxa span the large temporal gap between the oldest known diapsid Petrolacosaurus kansensis and the Late Permian neodiapsid Youngina capensis. These include two Middle Permian neodiapsids, the recently described Orovenator mayorum from Oklahoma, USA, and Lanthanolania ivakhnenkoi from the Mezen region, northern Russia. A recently collected, nearly complete skeleton of Lanthanolania permits a thorough reexamination of the phylogenetic relationships of these two taxa.

“Phylogenetic analysis of 188 characters and 30 diapsid taxa positions these two small forms as stem saurians and the oldest known neodiapsids (recently redefined by the authors as the sister taxon of Araeoscelidia). Interestingly, our results suggest that the lower temporal bar was lost by the ancestral neodiapsid relatively soon after the evolution of the diapsid temporal morphology, and conversely, that the temporal configuration of the Late Permian Youngina capensis is a secondary condition. In addition, the skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.”

Figure 1. Kuehneosaurid skulls from Palaegama to Coelurosauravus and Mecistotrachelos, and to Lanthanolania, Pamelina, Kuehneosaurus, Icarosaurus and Xianglong. Some of these taxa were not previously recognized as kuehneosaurids or their ancestors.

Figure 1. Kuehneosaurid skulls from Palaegama to Coelurosauravus and Mecistotrachelos, and to Lanthanolania, Pamelina, Kuehneosaurus, Icarosaurus and Xianglong. Some of these taxa were not previously recognized as kuehneosaurids or their ancestors.

Earlier (2011) the large reptile tree (LRT) nested Lanthanolania with the so-called rib gliders between Coelurosauravus and Icarosaurus. Back then we looked at those issues here.

Modesto and Reisz (2003) had a hard time
nesting Lanthanolania and considered it ‘enigmatic’. The closest they came was to nest Lanthanolania at the base of the lepidosauriformes (Rhynchocephalia + Squamata) and in other tests, with Coelurosauravus, which they split apart from the lepidosauriformes by adding intervening unrelated ‘by default’ taxa.

Unfortunately
with their small taxon list, Modesto and Reisz (2003) did not recover the basal split among reptiles that had occurred between the new Lepidosauromorpha and Archosauromorpha at Gephyrostegus + kin at the earliest Carboniferous. Thus the formerly monophyletic clade Diapsida is diphyletic in the LRT. Modesto and Reisz  mixed taxa from the two major clades and that muddied their results. Parts of their results were essentially correct, just unintelligible due to the addition of unrelated intervening archosauromorph basal diapsids.

Traditional paleontology
has likewise never nested coelurosauravids with kuehneosaurids, like Icarosaurus, perhaps based in part on the rib/dermal rod issue.

Problems and guesses:

  1. “Phylogenetic analysis of 188 characters and 30 diapsid taxa positions these two small forms as stem saurians and the oldest known neodiapsids (recently redefined by the authors as the sister taxon of Araeoscelidia).” — Sauria (= last common ancestor of archosaurs and lepidosaurs), is a junior synonym for Reptilia in the LRT. Neodiapsida (= includes all diapsids apart from araeoscelidians (= Petrolacosaurus and Araeoscelida)) or all taxa more closely related to Youngina than to Petrolacosaurus. Thus, in their thinking, Sauria is a clade within Neodiapsida. Modesto and Reisz do not yet recognize that Diapsida is no longer a monophyletic clade. In the LRT Orovenator and Lanthanolania are not related. The former is a basal diapsid archosauromorph. The latter is a basal lepidosauriform lepidosauromorph.
  2. “Interestingly, our results suggest that the lower temporal bar was lost by the ancestral neodiapsid relatively soon after the evolution of the diapsid temporal morphology,” — According to the LRT, the lower temporal bar was not lost nor was it present in the lepidosauromorph ‘rib’ gliders, including Lanthanolania. By contrast, Orovenator is one of the most basal archosauromorphs with an upper temporal fenestra.  Petrolacosaurus is older.
  3. “and conversely, that the temporal configuration of the Late Permian Youngina capensis is a secondary condition.” — In the LRT, it is not a secondary configuration, but is derived from basal diapsid taxa like Orovenator.
  4. “In addition, the skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.” — I can only guess why they promoted this hypothesis: short torso and long hind limbs? Icarosaurus has such proportions. So does Kuehneosaurus. So does their last common ancestor, Palaegama (Fig. 2) which lacks wire-like dermal ossifications.
Figure 3. Palaegama, close to the origin of all Lepidosauriformes.

Figure 2. Palaegama, close to the origin of all Lepidosauriformes.

The question today is
where is the paper that describes the above-mentioned post-crania of Lanthanolania? Is the post-crania definitely referable?

If the referred specimen came from similar sediments
the matrix was described in 2003 as ‘extremely hard to work with’. Perhaps it is still being worked on. Or it has been shelved.

Phylogenetic bracketing
indicates that the new specimen might or should have wing-like wire/rod dermal elements, like those found in both Coelurosauravus and Icarosaurus, but traditionally considered ribs in Icarosaurus. They are not ribs, as we learned earlier here. The real ribs are short and fused to the vertebrae, appearing to be long transverse processes, but no related taxa have long transverse processes and not all of the ribs are fused to the vertebrae, betraying their identity. Since a mass of dermal rods was not mentioned in the abstract, one  wonders if the new specimen was actually closer to Palaegama than to Lanthanolania?

Late news from Sean Modesto about Lanthanolania:
“The project is currently in the hands of Dr. Reisz. No “ETA” as yet!”

Problems like this one
are a good reason to include the taxa the LRT suggests one include in smaller, more focused studies.

References:
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Reisz RR and Modesto SP 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles.SVPCA abstract published online.

 

Weigeltisaurus skull reconstruction(s)

A new paper
by Bulanov and Sennikov (2015) reconstructs the holotype skull of Weigeltisaurus, a Permian gliding lepidosauriform (Fig. 1). We looked at this specimen earlier here guided by published drawings. Today we have a published photo of the specimen (see below). Previously Weigeltisaurus was considered a junior synonym of Coelurosauravus. Bulanov and Sennikov argue that Weigeltisaurus is a distinct genus.

Figure 1. Weigeltisaurus skull reconstructed by Bulanov and Sennikov (gray scale), and using DGS techniques (color). They did not attempt to trace the occiput, nor did they understand that the posterior crest is the supratemporal, displaced in situ and that the main portion is a very large squamosal that sweeps up. This skull is nearly identical to that of sister taxa, with the exception of the extended posterior elements, probably for secondary sexual selection. The same cannot be said of the Bulanov and Sennikov reconstruction which is, unfortunately, unique as is.

Figure 1. Weigeltisaurus skull reconstructed by Bulanov and Sennikov (gray scale), and using DGS techniques (color). They did not attempt to trace the occiput, nor did they understand that the posterior crest is the supratemporal, displaced in situ and that the main portion is a very large squamosal that sweeps up. This skull is nearly identical to that of sister taxa, with the exception of the extended posterior elements, probably for secondary sexual selection. The same cannot be said of the Bulanov and Sennikov reconstruction which is, unfortunately, unique as is.

Unfortunately
Bulanov and Sennikov made so many mistakes in their reconstruction that their arguments for retaining the genus Weigeltisaurus are difficult to support. Furthermore Bulanov and Sennikov do not reference sister taxa skulls to guide them through the process of reconstruction. Sister taxa include Jesairosaurus, Palaegama and Lanthanolania. Perhaps they do not know which taxa were sister taxa. The phylogenetic nesting of Coelurosauravus is typically not associated with kuehneosaurids and the taxa listed above. Finally, a phylogenetic analysis is missing.

The present interpretation 
differs from the Bulanov and Sennikov interpretation in several regards. They missed the occiput. I traced it. They did not include supratemporals. I interpret them here, displaced toward the jaw joint in situ. The saw a postorbital that was the exact mirror image of the postorbital process of the jugal. I interpret that as the other postorbital process of the jugal, flipped along with the frontals, which are exposed ventrally through the orbit. All of the bones are closely matched by sister taxa, like Jesairosaurus and differ largely and only in the secondary sexual character, the extension of the cranial frill.

If Bulanov and Sennikov
were going to separate Weigeltisaurus from Coelurosauravus they should have presented them both side by side.

By convergence
the cranial crest of Weigeltisaurus/Coelurosauravus is similar to that of the giant dinosaur, Styracosaurus and similar to that of helmeted chameleon Trioceros hoehnelii.

References
Bulanov VV and Sennikov AG 2015. Substantiation of validity of the Late Permian genus Weigeltisaurus Kuhn, 1939 (Reptilia, Weigeltisauridae) Paleontological Journal 49 (10):1101–1111.

Jesairosaurus and the drepanosaurs leave the Tritosauria :-(

My earlier reconstruction
of the basal lepidosauriform, Jesairosaurus (Fig. 1; contra Jalil 1997, not a protorosaur/prolacertiform) included several errors based on attempting to create a chimaera of several specimens of various sizes based on scale bars. In this case, scale bars should not have been used. Rather fore and hind parts had to be scaled to common elements, like dorsal vertebrae, as shown below (Fig. 2). I think this version more accurately reflects the in vivo specimen, despite its chimeric origins. All of the partial skeletons assigned to this genus were discovered at the same Early to Middle Triassic sandstone site and two were touching one another. A larger skull, ZAR 7, shows the variation in size from the skull to shoulders remains of the ZAR 6 specimen.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1997). The wide and flat ribs are interesting traits for a likely arboreal reptile.

Mother of all drepanosaurs
The Drepanosauria is an odd clade of slow-moving arboreal reptiles that includes Hypuronector, Vallesaurus, Megalancosaurus and Drepanosaurus (Figs. 2, 3). Jesairosaurus was not a drepanosaur, but nested basal to this clade before the present revisions. It remains basal to the Drepanosauria now with revisions.

The revised reconstruction of Jesairosaurus 
shifts this clade away from Huehuecuetzpalli, Macrocnemus and the rest of the Tritosauria. Now Jesairosaurus and the drepanosaurs nests between Saurosternon, Palaegama and the so-called “rib” gliders, beginning with Coelurosauravus.

A short history of Jesairosaurus
Shortly after their discovery Lehman 1971 referred the several hematite encrusted specimens to the Procolophonida. Further preparation showed that they were referable to the Diapsida, according to Jalil (1990) and the, more specifically, to the Prolacertiformes (Jalil 1997) as a sister to Malerisaurus with Prolacerta as a common ancestral sister. Jalil did not include the closest sisters of Jesairosaurus as revealed by the present analysis.

With a much larger list of taxa,
the large reptile tree nests Malerisaurus between the Antarctica specimen assigned to Prolacerta (AMNH 9520) and the holotype of Prolacerta. Jesairosaurus, as mentioned above, nests with the basal lepidosauriformes. Any traits shared with protorosaurs are by convergence. Deletion of Jesairosaurus does not affect the nesting of the Drepanosauria as basal lepidosauriformes.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Arboreal
This new nesting shifts drepanosaurs closer to kuehneosaurs (Figs. 3, 4), another notably arboreal clade.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Certainly
there will someday be more taxa to fill in the current large morphological gaps in and around Jesairosaurus, but here’s what we have at present (Fig. 3) with regard to the origin of the so-called “rib” gliders (actually dermal rods, not ribs, as shown by Coelurosauravus) and the origin of the drepanosaurs.

Figure 4. Jesarosaurus to scale with sisters Palaegama and Coelurosauravus.

Figure 4. Jesairosaurus to scale with sisters Palaegama and Coelurosauravus.

The shifting of a clade
like Jesairosaurus + Drepanosauria occurred due to inaccurate reconstructions used for data. Science builds on earlier errors and inaccuracies. I let the computer figure out where taxa nest in a cladogram of 606 possible nesting sites, minimizing the negative effects of bias and tradition.

It’s sad
to see the drepanosaurs leaving the Tritosauria as it contains several oddly Dr. Seuss-ian variations on the tritosaur theme.

Also note the nesting
of the basal Rhynchocephalians, Megachirella and Pleurosaurus, between the palaegamids and the tritosaurs (Fig. 4). In the course of this study, both also received updates to their skull reconstructions. The former was difficult to interpret without knowing where it nested. What appeared to be an odd sort of a squamosal in Megachirella now appears to be a pair of displaced pleurosaur-like premaxillae. For Pleurosaurus I should not have trusted a prior line drawing by another worker. Here I used DGS to create what appears to be a more accurate skull without so many apparent autapomorphies.

References
Jalil N 1990. Sur deux cranes de petits Sauria (Amniota, Diapsida) du Trias moyen d’ Algerie. Comptes Rendus de I’ Academic des Sciences, Paris 311 :73 1- 736.
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Lehman JP 1971. Nouveaux vertebres du Trias de la Serie de Zarzai’tine. Annales de Paleontologic (Vertebres) 57 :71-93.

 

 

Coelurosauravus wingless predecessor: Palaegama

Coelurosauravus (Fig. 1, Piveteau 1926, Late Permian ~250 mya, ~40 cm in length) was an arboreal lepidosauriform with an odd collection of dermal rods that opened laterally to produce ‘wings’ suitable for display or perhaps gliding. No one previously has produced an ancestor taxon.

Related taxa,
including Mechistotrachelos, Icarosaurus, Kuehneosaurus and Xianglong, produced variations on the Coelurosauravus design, all convergent with the living rib-glider, Draco, an iguanid not related to any of the above taxa.

Coelurosauravus also has wide, temporal crests shared only with Mecistotrachelos. Earlier we discussed the homology of the dermal rods (not ribs) of kuehneosaurs with those of Coelurosauravus.

Figure 1. Palaegama and Coelurosauravus to scale. The latter has dermal rods that frame gliding/display membranes.

Figure 1. Palaegama and Coelurosauravus to scale. The latter has dermal rods that frame gliding/display membranes. No other taxon nests closer to the base of the gliding clade.

The outgroup taxon
in the large reptile tree for these odd arborealists is Palaegama (Fig. 1, Carroll 1975). It preserves no hint of lateral dermal rods and has no temporal crest. It is such an unpopular taxon that it has not yet earned a Wikipedia entry. Among 588 taxa in the large reptile tree, no other is closer to Coelurosauravus and the kuehneosaurs.

As a basal lepidosauriform, 
Palaegama (Late Permian) also nests with the basalmost lepidosaurs, including the basalmost sphenodontid, Megachirella, the basalmost tritosaur Tijubina (Early Cretaceous) and the basalmost pre-squamate, Lacertulus (Late Permian), all ‘lizardy’ taxa of similar morphology.

So
Palaegama is really an important taxon nesting near the bases of several clades. It deserves more press, scrutiny and credit.

Distinct from predecessor taxa,
Palaegama has long strong limbs and long digits, like those of its headless sister, Saurosternon. The Palaegama skull is wide and flattened. Due to these traits it is possible that Palaegama leaped from tree to tree prior to the addition of lateral membranes stiffened with fibers.

Carroll (1975, 1977)
understood that Palaegama might have had a role in the origin of lizards, but those publications preceded computer-assisted phylogenetic analysis and Carroll was not aware of the pre-squamate and tritosaur clades, nor did he make the connection to Coelurosauravus.

A large gamut cladogram is ideal for solving many such problems.

References
Carroll RL 1975. Permo-Triassic ‘ lizards ’ from the Karroo. Palaeontologia africana 18, 71–87.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.

The skull of Xianglong – Early Cretaceous kuehneosaur

Xianglong zhaoi (Li et al. 2007) Yixian Formation, Early Cretaceous, 15.5 cm in length was originally considered an agamid lizard with elongated transverse processes and hyperelongated ribs, like the extant Draco volans. However Xianglong has a larger suite of traits shared with Kuehneosaurus and Icarosaurus. Not a lizard, Xianglong was a kuehneosaur that survived into the Cretaceous. That clade nests outside of the Lepidosauria in nearly all cladograms including the large reptile tree.

The skull was complete, but thoroughly crushed (Fig. 1).

Figure 1. Xianglong animated GIF file. Here DGS (digital graphic segregation) is the technique used to pull bone shapes out of this apparent chaos. Many of the bones overlap others and many long bones are broken. See figure 2 for the reconstruction. The light green vomers here are gold in figure 2.

Figure 1. Xianglong animated GIF file. Here DGS (digital graphic segregation) is the technique used to pull bone shapes out of this apparent chaos. Many of the bones overlap others and many long bones are broken. See figure 2 for the reconstruction. The light green vomers here are gold in figure 2.

The animated GIF (Fig. 1)
shows skull and mandible/hyoid elements on segregated layers using digital graphic segregation (DGS). Below (Fig.2) in the second half of any DGS process, those elements are reset to reproduce the skull in dorsal, palatal and lateral views.

Figure 1. Xianglong zhaoi, a late-surviving sister to Kuehneosaurus and Icarosaurus. What appear to be ribs framing the gliding membrane are in fact dermal ossifications as in Coelurosauravus.

Figure 1. Xianglong zhaoi, a late-surviving sister to Kuehneosaurus and Icarosaurus. What appear to be ribs framing the gliding membrane are in fact dermal ossifications as in Coelurosauravus.

Figure 2. Skull elements of Xianglong reconstructed in several views. Some soft tissue is also shown (light green). Elements pulled from figure 1. If you find any errors here, please call them to my attention.

Figure 2. Skull elements of Xianglong reconstructed in several views. Some soft tissue is also shown (light green). Elements pulled from figure 1. If you find any errors here, please call them to my attention.

The reconstruction
is rather straightforward, moving elements back into their in vivo positions. Some elements seen edge-on, like the skull roof in lateral view, are either freehanded to the correct length and curved to fit, or reduced in one direction using the scaling tool of Photoshop. Note the great resemblance of this skull to that of a sister taxon, Kuehneosaurus (Fig. 4).

Figure 3. Xianglong overall. Note the detail recovered in the tracing of the skull here. These authors had the original in their hands, yet DGS was able to pull more data out using published photos.

Figure 3. Xianglong overall. Note the detail recovered in the tracing of the skull here. These authors had the original in their hands, yet DGS was able to pull more data out using published photos.

The skull of Xianglong
was originally traced with little regard to details (Fig. 3). DGS (Fig. 1) was able to pull those details out in a matter of hours from the published literature. Despite the large number of current detractors, DGS has value. This is just one of many such demonstrations.

The Triassic kuehneosaur gliders and their non-gliding precursors.

Figure 4. Click to enlarge. The Permian, Triassic and Early Cretaceous kuehneosaur gliders and their non-gliding precursors. Included are Coelurosauravus, Mecistotrachelos, Kuehneosaurus, Icarosaurus and Xianglong, all with extended dermal processes mimicking ribs. Palaegama and Saurosternon do not have these gliding/display elements.

Draco volans (Fig. 5) is an extant iguanian squamate lepidosaur with genuine elongate ribs framings its gliding membrane. Note the distinct skull shape. Also note the complete lack of elongate transverse processes on the dorsal vertebrae. Those elongate so-called transverse processes on kuehneosaurs are often, but not always the actual ribs, fused to the vertebrae (the proportion of rib to transverse process changes along each spinal column), as discussed earlier here in yet another heretical observation at odds with current paleontological conventions and paradigms.

Figure 6. Draco volans a living true rib glider. Note the distinct skull morphology, closer to that of Iguana than to Xianglong.

Figure 5.  Draco volans a living true rib glider. Note the distinct skull morphology, closer to that of Iguana than to Xianglong.

References
Li P-P, Gao K-Q, Hou L-H and Xu X. 2007. A gliding lizard from the Early Cretaceous of China. PNAS 104(13): 5507-5509. doi: 10.1073/pnas.0609552104 online pdf

wiki/Xianglong