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.

 

 

Secondary sexual behavior in Longisquama (and Cosesaurus)

Sure Longisquama had giant plumes
that likely entranced the lay-dees… and/or the gents…

But as the proximal outgroup to the Pterosauria,
and provided with a similar pectoral girdle (sternal complex, strap-like scapulae, quadrant-shaped coracoids, it was a likely flapper, as we talked about earlier here with similar traits in Cosesaurus (Fig. 1)

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 1. Click to enlarge and animate. Cosesaurus flapping.

Here (Fig. 2) is an animated Longisquama, flapping and with tail wags, which we talked about earlier here.

Figure 2. Click to animate. Longisquama flapping and wagging its tail.

Figure 2. Click to animate. Longisquama flapping and wagging its tail.

With these traits and behaviors basal fenestrasaurs converged with theropods ancestral to birds. In these ways flapping preceded powered flight, in both cases co-opted from secondary sexual behaviors in these highly visual reptiles.

Gliding Lizard Diversity and Data – This You Gotta See!

Just a quick hit to alert you to a fascinating blog page on gliding lizards.

Figure 1. Gliding lizard Draco volans with ribs extended.

Figure 1. Gliding lizard Draco volans with ribs extended. Click to see more.

Dozens of photos. Lots of background and cool information.

You can find it here.

More on prehistoric gliding lepidosauriforms (not squamates, not lepidosaurs) here and here. Earlier we talked about the evolution of this “rib” gliders here.

Rethinking the “fused ribs” of Triassic gliders

Living from the Permian through the Cretaceous, the so-called “rib” gliders are an interesting lot. And I’m still trying to figure out what’s going on with the ribs and transverse processes. All their closest kin have ribs and none have transverse processes. Here’s the latest (a very minor change of thinking):

Coelurosauravus.

Figure 1. Coelurosauravus. It had ribs, but no transverse processes. The extradermal rods were more numerous than the ribs. Click to learn more.

Coelurosauravus (Fig. 1) is the earliest one (Late Permian). It had no transverse processes. It had ribs. It had extradermal rods likely supporting membranes, and many more rods than ribs anteriorly, but that became a one-to-one relationship posteriorly.

The other rib gliders were distinctly different. Icarosaurus (Fig. 2), Kuehneosaurus (Fig. 3), Mecistotrachelos and Xianglong all had long transverse processes, few to no ribs and the extradermal rods matched one to one with the transverse processes.

Traditional thinking (everyone else) considers the gliding membrane rods to be the ribs, following the pattern of Draco (Fig. 4), the living and genuine rib glider, which likewise has no transverse processes.

Since no other close taxa to the extinct “rib” gliders had transverse processes this led to the heretical idea that the long transverse processes WERE the ribs now fused to the centra and that the gliding spars continued to be extradermal in origin, as in Coelurosauravus (Fig. 1).

Icarosaurus.

Figure 2. Icarosaurus. Note the tiny ribs near the shoulders. Or are those unfused ribs?

Icarosaurus and Kuehneosaurus display mid-change solutions. They have short transverse processes anteriorly and long ribs. They also have long transverse processes starting at the shoulder and tiny to no ribs. Look closely. You’ll see them.

Kuehneosaurus.

Figure 3. Kuehneosaurus. Note the elongation of the transverse processes replacing the gradually shortening ribs posteriorly.

This is different from the situation in the convergent and largely unrelated living glider, Draco (Fig. 4) in which there are no transverse processes and those membrane spars definitely are the dorsal ribs. The spars on Icarosaurus (Fig. 2) are waaaay too long to be even considered as ribs.

Draco volans

Figure 4. Draco volans in dorsal view based on an X-ray. Click for more info.

Ultimately, I now see the evolution of increasingly longer transverse processes (restricted only to members of this clade) and the reduction of the ribs, not their fusion as I thought before. So, dermal extensions attached directly to transverse processes and the ribs are missing posteriorly.

Not sure how the rest of the gut was supported, or how the lungs expanded without traditional ribs. These oddballs figured out some other way to respire.

The trend was for a shorter body and fewer membrane spars taken to extremes in the most derived of these gliders, Mecistotrachelos and Xianglong, which was originally considered a lizard related to Draco. Here’s the family to scale.

The Triassic gliders and their non-gliding precursors.

Figure 5. Click to enlarge. The Triassic gliders and their non-gliding precursors.

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.

This marks the 500th post. 

Microraptor and Longisquama: Convergent Evolution of 4 Wings

A recent paper (Li et al. 2012) on the iridescence of the feathers of the four-winged dromaeosaur, Microraptor (Xin et al. 2003) prompted this report on its convergence with the four-winged fenestrasaur, Longisquama (Sharov 1970). Both, it seems, devoted much of their anatomy to attracting mates and extending their glides from tree to tree.

Microraptor gui

Figure 1. Microraptor gui, the four-winged dromaeosaur. Arrows point to flight feathers on the forelimbs and hindlimbs. From Xing et al. 2003.

Longisquama had Four Wing, too.
The traditional paradigm holds that the back half of Longsiquama remains unknown, but DGS (digital graphic segregation) identifies all the elements of the entire skeleton of Longisquama (illustrated here). With trailing membranes on both the forlimbs and hindlimbs, Longisquama was a four-winged flapping glider, and a model ancestor for the two-winged pterosaurs, with which it shared a longer list of traits than any other known reptile, as recovered form the large reptile family tree.

 

Figure 2. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Figure 2. Longisquama in lateral view, dorsal view and closeup of the skull. Like Microraptor, Longisquama glided/flew with similarly-sized wings both fore and aft.

Secondary Sexual Characteristics Coopted for Flight
Like Microraptor, Longisquama was overloaded with secondary sexual characteristics. From plumes to flapping arms, Longisquama was all about creating an exciting presentation unrivaled until the present-day bird-of-paradise. Longisquama had everything Cosesaurus had, only wildly exaggerated. With increased bipedalism and active flapping, Longiquama probably experienced the genesis of aerobic metabolism.

Microraptor restored.

Figure 3. Microraptor restored. Hind limbs are artificially splayed. From Li et al. 2012.

Comparisons
Microraptor did not develop a set of dorsal scale/plumes like Longisquama. That was a lepidosaur trait gone wild (contra Buchwitz and Voigt 2012 who nested Longisquama between traditional lepidosauromorphs and traditional archosauromorphs). Microraptor did not splay its hind legs like Longisquama. That’s another lepidosaur trait. They shared a similar size and general body proportions, including long strong hind limbs and a long attenuated tail. Microraptor extended the length of its hands with feathers. Longisquama did so with an extended fourth finger provided by a trailing membrane. The hind limbs of Microraptor were provided with trailing membranes, in this case, flight feathers. The hind limbs of Longsiquama were provided with trailing uropatagia, as in sister taxa, Sharovipteryx and pterosaurs. Both Microraptor and Longisquama flapped their forelimbs because both had elongated, immobile, stem-like coracoids anchored to sternae and slender strap-like scapulae. These elements also anchored enlarged pectoral muscles for flapping. Both were able to perch on tree branches. Microraptor employed a reversed pedal digit 1 to wrap around the back of a branch opposite the anterior toes. Like basal pterosaurs, Longisquama used the dorsal side of a hyperflexed pedal digit 5 as a universal wrench (Peter 2002) to press on the top of the branch, opposite the anterior toes wrapping around the bottom of the branch. Both Microraptor and Longisquama had anteriorly elongated ilia, more than two sacrals, a tibia longer than the femur and digitigrade feet. Both were obligate bipeds.

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
Buchwitz M and Voigt S 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift (advance online publication) DOI: 10.1007/s12542-012-0135-3
Li Q, Gao K-Q, Meng Q,Clarke JA, Shawkey MD, D’Alba L, Pei R, Ellison M, Norell MA, and Vinther J 2012.
 Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science 9 March 2012: 335 (6073), 1215-1219. [DOI:10.1126/science.1213780]
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15:277-301.
Turner AH, Diego P, Clarke JA, Erickson G and Norell, M 2007. A basal dromaeosaurid and size evolution preceding avian flight. Science, 317: 1378-1381. doi:10.1126/science.1144.
Xing X, Zhou Z, Wang X,  Kuang X, Zhang F and Du X 2003. Four-winged dinosaurs from China. Nature 421: 335–340.

The Hands of Sharovipteryx

The hands of Sharovipteryx have been considered “missing” since Sharov (1971) did not illustrate them, other than finger 4 of the left hand.

Sharov's illustration of finger 4.

Figure 1. Sharov’s illustration of finger 4.

I Blame It on Soft Tissue
Sharovipteryx preserves soft tissue from it s scaly snout to its webbed toes. Soft tissue also obscured the hands on the counterplate. Here (Fig. 2) I traced what faint impressions remained of the fingers using DGS (digital graphic segregation). Yes, it’s difficult to discern. Whether illusions or not, both hands matched each other and their ratios and patterns matched or were transitional between those of sister taxa, Cosesaurus and Longisquama.

The pectoral girdle and forelimbs of Sharovipteryx.

Figure 2. The pectoral girdle and forelimbs of Sharovipteryx. Both sides match each other and fit neatly into their phylogenetic node between sisters Cosesaurus and Longisquama.

Reconstruction
The reconstructed hand of Sharovipteryx (Fig. 3) had the appearance of a stunted limb, with a reduced yet robust humerus and radius+ulna. Certainly neither supination nor pronation was possible. A pteroid was retained. Unlike the other basal fenestrasaurs, all four metacarpals were subequal in length. Metacarpal 4 was more robust than the others and its terminal articular surface was expanded, as in pterosaurs. Digit 4 was also more  robust, especially proximally, as in pterosaurs. The claws were sharp, but not especially trenchant. The PILs (parallel interphalangeal lines) were continuous across all four digits indicating that all the phalanges flexed as phalangeal sets, as in other tetrapods, other than Longisquama and pterosaurs.

The reconstructed hand of Sharovipteryx.

Figure 3. The reconstructed hand of Sharovipteryx. The proximal elements were reduced. Despite the appearance here of a rotated metacarpal 4, the PILs remained continuous indicating that digit 4 probably had not rotated (as in pterosaurs and Longisquama), but remained a part of the flexion set. Even so metacarpal 4 was enlarged relative to the others, so the wing-making process had begun. 

Evolutionary Significance
Even though Sharovipteryx is the sole representative of a distinct fenestrasaur branch in which the hind limbs were emphasized, the forelimbs were de-emphasized and the neck was elongated, it still demonstrated traits illustrating the evolution of pterosaurian traits beyond those of Cosesaurus, but not  to the level of Longisquama.

Usefulness?
Were the hands of Sharovipteryx useless vestiges? Or were they important canards used aerodynamically to affect pitch control? The hands of Sharovipteryx were likely trailed by soft tissue membranes, since both taxa in its phylogenetic bracket (Cosesaurus and Longisquama) had such membranes. With a robust stem-like coracoid, Sharovipteryx was able to flap its arms, providing only a small amount of thrust. Thrust vectoring would have been most useful to raise the front of the body during a landing in order to stall the large hind-leg wing and execute a gentle two-point landing. It is hard to imagine the small hands of Sharovipteryx used to cling to tree trunks, but perhaps they did so if Sharovipteryx bellied up to a big one.

 

Figure 2. Sharovipteryx mirabilis in various views. No pycnofibers added yet. Click to learn more.

Figure 4. Sharovipteryx mirabilis in various views. Trailing membrane on the hand is guesswork based on phylogenetic bracketing. Click to learn more.

Was Metacarpal 4 Rotated?
Good question. Hard to tell. Some evidence points one way. Other evidence does not. Perhaps this stage is the transition one. That makes sense for several reasons.

We’ll look at the skull next…

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
Dyke GJ, Nudds RL and Rayner JMV 2006. 
Flight of Sharovipteryx mirabilis: the world’s first delta-winged glider. Journal of Evolutionary Biology.
Gans C, Darevski I and Tatarinov LP 1987. Sharovipteryx, a reptilian glider?Paleobiology, October 1987, v. 13, p. 415-426.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Sharov AG 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].

wiki/Sharovipteryx

Mecistotrachelos, the Walking Stick “Rib” Glider

Among the Permo/Triassic so-called “rib” gliders is an oddball with a walking-stick sort of torso with fused ribs no wider than its centra. The oddball is Mecistotrachelos from the Late Triassic and it was a sister to Coelurosauravus of the Late Permian.

Mecistotrachelos

Figure 1. Mecistotrachelos, the walking stick "rib" glider in lateral view except for the dorsal series and pseudoribs, which are seen in dorsal view. pseudoribs folded above, and extended below. The tail length is unknown.

Mecistotrachelos apeoros (Fraser et al. 2007) Late Triassic ~210 mya, demonstrates variety in later derived clade members with fewer dorsal vertebrae and fewer pseudoribs. The body was extremely slender, almost stick-like, with hyper-elongated cervicals and greatly reduced ribs fused to each centrum. The limbs were more gracile and the tail length is unknown. The fibula was fused or closely adhered to the tibia.

The long neck would have made Mecistotrachelos an unstable glider according to Fraser (2007). Coelurosauravus had a long neck and a larger skull. Were the dermal struts deployed for gliding? For display? Or both? Like other kuehneosaurs, Mecistotrachelos had small teeth and was likely an insectivore. Fraser (2007) wondered if his find was an archosauromorph. It is not. Here Mecistotrachelos nested with Coelurosauravus among the lepidsauromorpha, within the lepidosauriformes.

Not Like Draco the Extant Glider
Fraser (2007) reported, “The new form is characterized by the presence of extremely elongate thoracolumbar ribs that presumably supported a gliding membrane in life.” Fraser (2007) notes kuehneosaurs had “ribs forming hinge joints with the markedly elongate transverse processes on the dorsal vertebrae.” This is wrong. No Mecistotrachelos sister taxa had elongated transverse processes. The apparent transverse processes ARE the ribs, fused to the vertebrae, derived from the condition seen in the short ribs of Coelurosauravus (Fig. 2). The pseudoribs were actually elongated dermal ossicles described as “bundles of rodlike neomorph ossifications,” by Fraser (2007) quoting Frey et al. (1997). By contrast, in Draco the gliding struts are indeed elongated dorsal ribs.

The Triassic gliders and their non-gliding precursors.

Figure 2. Click to enlarge. The Triassic gliders and their non-gliding precursors.

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
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.

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

Icarosaurus, Kuehneosaurus and the So-Called “Rib” Gliders

An Introduction
While pterosaurs were experimenting with flapping flight in the Late Triassic, several arboreal lepidosauriforms were gliding with hyper-elongated, rib-like, dermal extensions anchored to their reduced and modified ribs. Welcome to the world of the Triassic gliders, their Permian precursors and their one and only known successor in the Early Cretaceous, Xianglong.

Coelurosauravus reconstructions

Figure 1. Coelurosauravus reconstructions from Carroll, Frey et al and Peters.

Traditional and Published Views
Carroll (1978, 1988) separated Coelurosauravus from Icarosaurus + Kuehneosaurus. The former was considered a primitive diapsid and the latter two were considered lizards. Both were reported to extend lateral gliding membranes framed by elongated ribs, as in the modern gliding lizard, Draco. Like Draco, no transverse processes were reported in Coelurosauravus (Figure 1), but large transverse processes were reported in Icarosaurus + Kuehneosaurus. Then Frey et al. (2007, Figure 1) found short ribs in Coelurosauravus, which meant the gliding membrane extensors were ossified dermal rods. They reported, “The rods are independent of the ribcage and arranged in distinct bundles to form a cambered wing.” Finally, the Early Cretaceous glider, Xianglong, was reported (Li et al. 2007) to be an agamid lizard, like Draco.

The Triassic gliders and their non-gliding precursors.

Figure 1. Click to enlarge. The Triassic gliders and their non-gliding precursors.

The Heretical View
Here sets of anterior dermal rods of Coelurosauravus were bundled and anchored to the tips of the anterior two ribs while the posterior rods were associated one-to-one with individual dorsal ribs. Here the purported transverse processes of Icarosaurus and Kuehneosaurus are short, straight ribs fused to their centra and the purported “ribs” are dermal rods, as in Coelurosauravus. Here Coelurosauravus is a sister to Icarosaurus + Kuehneosaurus and all three are non-lepidosaur lepidosauriforms. Finally, Xianglong also had short, straight ribs fused to their centra and so was related to Icarosaurus + Kuehneosaurus, not Draco.

Traditional Origins
There are as many origins and nesting for the “rib” gliders as there are studies that include them. Laurin 1991 nested Coelurosauravus between the diapsid Petrolacosaurus and the synapsid Apsisaurus. Evans 1988 nested Coelurosauravus between Mesenosaurus and Claudiosaurus. Kuehneosaurs nested in two places, between Choristodera and rhynchosaurs and also between Saurosternon and Gephyrosaurus + Squamata. Evans 2003 nested kuehneosaurs between archosauromorpha (prolacertiforms, rhynchosaurs, archosauriforms) and Marmoretta. Motani (1998) neste kuehneosaurs between lizards and sauropterygians. Müller (2003) nested kuehneosaurs and Coelurosauravus together between Claudiosaurus and Ichthyosaurs + thalattosaurs. The latter seems especially unlikely, nesting aerial reptiles with marine taxa.

Nesting Within the Larger Study
The larger study nested the gliders together with Saurosternon and Palaegama as outgroup taxa.

Let’s Begin with Palaegama
Palaegama was a Late Permian lepidosauriform blessed with elongated arms and legs. These would have been useful living in trees, or perhaps sprinting on the ground bipedally. Palaegama has been recognized as a basal lepidosauriform along with Saurosternon and Paliguana.  Estes, Pregill and Camp (1988 ) reported, “they share more features of modern lizards than do any other reptiles of the lat Paleozoic and early Mesozoic.” Yet they were not lizards. They were lizard predecessors. In particular, the skull shape and naris placement of Palaegama indicate a close relationship with Coelurosauravus.

Saurosternon
(Latest Permian/Earliest Triassic) Saurosternon was smaller, but with relatively larger feet. Twin sternae appear posterior to the coracoids. These likely indicated an increase in humerus adduction, as in tree clinging. The shorter body shape indicates a closer relationship to Icarosaurus than to Coelurosauravus.

Coelurosauravus
(Late Permian) Coelurosauravus was longer, leaner, with a more exotic skull, shorter ribs and more gracile limbs. Elongated dermal ossicles anchored on the rib tips, were able to fold and extend huge lateral membranes, probably for gliding, but also useful as secondary sexual characters (again, check out that skull for exotic extremes).

Mecistotrachelos
(Late Triassic) Mecistotrachelos was a coelurosauravian with a longer neck, shorter tail and a much more slender (almost stick-like) torso in which the ribs were fused to the centra, making them appear to be transverse processes. Fewer dermal “pseudo-ribs” were used to frame the gliding membrane. The cranial crest remained, but was reduced.

Lanthanolania
(Late Permian) only the skull has been published (Modesto and Reisz 2003), and it was originally considered an enigma, but its affinities are with Icarosaurus and the gliders. In a recent abstract, Reisz and Modesto (2011) reported, “The skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.” Unfortunately, Lanthanolania was not a diapsid. Nor was it as old as Eudibamus, another diapsid biped. Apparently it also does not have extended pseudoribs, otherwise, they would have been mentioned.

Icarosaurus
(Late Triassic) Icarosaurus transformed the short ribs of Saurosternon into short “transverse processes” fused to the centra. This transformation has been overlooked by other paleontologists, who report that Icarosaurus had extended ribs, like Draco, the living rib glider. The problem is, no sister taxa have transverse processes, Draco doesn’t have transverse processes, several unfused ribs appear between the scapulae in Icarosaurus and the phylogenetic precursors have not been identified as they are here. In any case, a short tail, deep pelvis and short torso characterize this genus.

Kuehneosaurus
(Late Triassic) The biggest of the gliders, Kuehneosaurus was most similar to Icarosaurus but had feet much larger than the hands. Certain posterior (fused) ribs angled anteriorly.

Xianglong
(Early Cretaceous) Xianglong was considered an agamid lizard by Li et al. (2007), but it clearly had short “transverse processes” (actually ribs fused to centra) not found in agamids like Draco. Xianglong demonstrates the survival of the PermoTriassic gliders into the Cretaceous. A poorly ossified carpus may indicate immaturity in the one known specimen.

Summary
The PermoCretaceous gliders reduced the dorsal ribs, fused these to the centra and developed elongated dermal extensions to extend lateral gliding membranes. Coelurosauravus and its membranes were considered distinct and convergent, but here they were homologous with those of kuehneosaurids. Xianglong was a late-surviving non- lepidosaur lepidosauriform.

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
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.

wiki/Coelurosauravus
wiki/Mecistotrachelos
wiki/Kuehneosaurus
wiki/Xianglong
wiki/Icarosaurus