Pterosaurs NOT an enigmatic group, contra Belben and Unwin 2019

The following abstract
was presented during the most recent SVPCA meeting in 2019.

Belben and Unwin 2019
are both associated with the University of Leicester. Sadly, Dr. Unwin has been responsible for many of the inaccurate to totally wrong ideas many current pterosaur workers and artists now consider as canon. Think Sordes and the deep chord bat-wing membrane stretching to the ankles hypothesis and the incorporation of pedal digit 5 into the single uropatagium stretching between the two. Think pterosaur eggs laid deep under brush or under ground. Think the archosaurian genesis for pterosaurs. Think the Monofenestrata hypothesis of relationships.

I’ll break down today’s abstract for you
as yet another example of Dr. Unwin stuck in his own groove outside of science and reality, much of it due to inaccurate observation and taxon exclusion, both of which are curable maladies.

From the Belben and Unwin 2019 abstract:
“Quantitative taphonomy [see below for definition] has huge potential for furthering our understanding of vertebrate palaeobiology. So far, however, it has been a neglected field with little development. Here we show how quantitative taphonomy can be used to determine the ‘bauplan’ of pterosaurs.

With well over 250 good fossils, many complete skeletons, some of these with extensive soft tissue, we already know the ‘bauplan’ of pterosaurs very well (Fig. 1). Start here for an introduction and links.

“With no descendants and a unique morphology, pterosaurs remain an enigmatic group despite a high degree of research interest for over 200 years.”

Pterosaurs do not have a unique morphology, nor are they an enigmatic group. Peters 2000a b, 2002, 2007, 2009 showed the pterosaur ‘bauplan’ arose gradually from a clade of taxa Dr. Unwin refuses to recognize, the Fenestrasauria, nor does he cite the above references. Dr. Unwin prefers to keep his objects of study in the ‘enigmatic’ jar for reasons that should baffle any reputable scientist. If you wonder why I have to self-cite, welcome to the world of paleo politics where academics don’t argue against a hypothesis, they don’t cite it.

“One aspect still debated is the basic construction and extent of the wing membrane, fundamental to locomotory abilities and other key aspects of their biology.”

The wing membrane question was settled over a decade ago and need not be debated because every example of pterosaur wing membrane presents the same conservative pattern: stretched between elbow and wing tip with a fuselage fillet. (Peters 2002). Precursor membranes are known in Cosesaurus (Peters 2009) and are less obvious in Longisquama. The pteroid and preaxial carpal arise from a migration of two centralia (Peters 2009). Details summarized here.

“Did the wing membrane connect all four limbs, bat-like, forming a single flight surface and single anatomical module? Were they bird-like, with separation of limbs to create four anatomical modules? Or were they a unique two or three module construction?”

This has never been a question for Dr. Unwin before. He has always promoted the invalid bat-like wing design and the invalid single uropatagium design.

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

Figure 1. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees and a precise impression of the wing membranes as they were. The animation extends the limbs into the flight configuration.  

“Soft tissue evidence is patchy and found in only a tiny number of species, and the insights it provides is limited.”

False. Dr. Unwin knows better. There are many excellent examples of soft tissue only one of which (Fig. 1) would be necessary to answer the wing membrane and uropatagia issues. The rest confirm the first (Peters 2002).

“Quantitative taphonomy, through metrics of completeness, articulation, and joint geometry, can test limb association, and help identify anatomical modules.”

Dr. Unwin, why don’t you stop avoiding the number one issue and just once accurately trace your first pterosaur specimen with soft tissue. Study it. Play with it. Reconstruct it. Animate it. Score it for a wide range of traits against all the 240 best known pterosaur specimens, as shown here. I think you’ll find the process enlightening and you’ll finally be able to teach your students something about your favorite subject without cloaking pterosaurs in question marks. Don’t be seen as the bumbling professor who held back pterosaur research for several decades by sticking to your invalid postulates. When the word gets out, you may find it hard attracting students, which is your livelihood.

Examining the quantitative taphonomy (= depositional setting, = everything but the pterosaur itself) only delays the inevitable day of reckoning when you will have to finally, seriously and precisely trace a pterosaur specimen and present your findings for critical review.

“Over 100 pterosaurs have been analysed thus far, with an intended data set of 200+ individuals from more than 40 species representing all principal clades. This will allow different models to be mapped across the phylogeny.”

Are you examining the quantitative taphonomy of 200+ individuals or the 200+ individuals themselves? Sounds like the former is in play. Please don’t attempt to map the different taphonomic models across your incomplete cladogram to find out what a pterosaur ‘bauplan’ is. Instead, start with the Vienna specimen of Pterodactylus (Fig. 1). Get precise with it. Don’t pass the chore down to a grad student seeking approval and fearing for their grade. Use the large pterosaur tree (LPT, 240 taxa) for sister taxa. Trace and reconstruct your own specimens. You can pull yourself out of your self-inflicted academic muck!

“Fossil birds and bats will be similarly analysed in order to provide context and constrain the models, as their bauplan can be safely inferred from extant forms.”

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 – 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.

That’s nice. But birds and bats are not related to pterosaurs nor to each other. Why not stop wasting your time and go see Cosesaurus, Sharovipteryx and Longisquama. Don’t forget Langobardisaurus, Macrocnemus and Huehuecuetzpalli. Don’t stop until you can reconstruct and score them in your sleep. Dr. Unwin, you’re stuck in the tail-dragging dark ages. You’re supposed to be a pterosaur expert, so quit calling them enigmas. You need to turn your mind around. The following citations might help.


References
Belben R and Unwin D 2019. Quantitative taphonomy – they key to understanding the pterosaur bauplan?
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.

Quantitative taphonomy = “This approach uses the hypothesis that taphonomic alteration varies in a predictable way with depositional setting. In other words, each specific environment (e.g., low-salinity muddy bay, storm-dominated clastic shelf) is characterized by a unique suite of physical, chemical and biological processes: these processes imprint a unique and predictable “taphonomic signature” on the death assemblage.” Davies et al.  2017

 

What Dr. Ellenberger saw in Cosesaurus (soft tissue)

With the Rio Pterosaur Symposium 2013 coming to end, I thought it appropriate to bring out one of the most important taxa in the study of pterosaurs. Ironically no one else, including its discoverer, seems to think so, except yours truly. At the two previous symposia, Dr. Peter Wellnhofer lamented, “We still don’t know where pterosaurs come from. We have no Archaeopteryx for pterosaurs.” I imagine, if he is attending the Rio symposium, he and the other traditional workers continue this lament — all of which is their own fault because they have their scientific blinders on.

So did Dr. Paul Ellenberger (1974, 1978, 1993), the first scientist to describe the small, complete, beautifully preserved impressions of a little Middle Triassic lepidosaur, Cosesaurus aviceps. Ellenberger looked at Cosesaurus more thoroughly over a longer period of time than any other worker and all he saw was a bird ancestor. Earlier here and here we looked at what details Dr. Paul Ellenberger saw in Cosesaurus, focusing on the impressions of bones. Here we’ll focus on the impressions of soft tissues. I can confirm, through personal observation of the original fossil, that these impressions are indeed present. Anyone else with a ticket to Barcelona can test these observations themselves.

Cranial frill of Cosesaurus compared to that of a Hoatzin. Image by Pierre Ellenberger (1993).

Figure 1. Cranial frill of Cosesaurus compared to that of a Hoatzin. Image by Paul Ellenberger (1993).

The cranial frill (Fig. 1), like that of other lepidosaurs from Basilisk to Sphenodon, may have been retained and ossified by derived pterosaurs. Such a decoration attests to a secondary sexual trait and a possible cooling surface for this facultatively bipedal flapping sprinter. There also appears to be a thin vertical plate over the nasals, likely produced by the premaxilla ascending process. Such decorations come and go in pterosaurs and their kin.

Figure 2. Dorsal frill of Cosesaurus. Image by Pierre Ellenberger (1993).

Figure 2. Dorsal frill of Cosesaurus. Image by Paul Ellenberger (1993). That “sternal keel” is the stem-like quadrant-shaped coracoid identical to that in early pterosaurs.

Tail of Cosesaurus. Image by Pierre Ellenberger (1993). Note fibers emanating from tail.

Figure 3. Tail of Cosesaurus. Image by Paul Ellenberger (1993). Note fibers emanating from tail.

The dorsal frill of Cosesaurus (Fig. 2) was inherited from Sphenodon and Huehuecuetzpalli and found the acme of its expression in Longisquama. It looks short, but continue those lines to the vertebrae and they become substantial in length.

The caudal fibers of Cosesaurus (Fig. 3) were further decorations that Ellenberger considered pre-feather shafts, but are actually just fibers, some of which near the tail tip would ultimately coalesce to become a pterosaur tail vane.

Actinofibrils also emanated from the posterior of each forelimb (Fig. 4). These would ultimately become  pterosaur wings and falsify the hypothesis that pterosaurs started as gliders with proximal extradermal membranes (as in gliders). In Cosesaurus and its descendants flapping the arms while running with these fibers ultimately added thrust sufficient for flight.

Fibers and membranes emanating from the hind limbs attest to the origin of paired uropatagia in Sharovipteryx and pterosaurs. Note the presence of fibers around the knee. These attest to an insulation layer, either to trap heat or keep biting insects away from the skin.

There are very few traits that pterosaurs have that are not also found in Cosesaurus, other than the elongated manual digit 4 that framed the enlarged wing. Even so, even this trait has its genesis in Cosesaurus. Paul Ellenberger (1993) certainly made mistakes in biasing his interpretation toward birds, but he is also to be commended for his careful observations of various soft tissue impressions that are key to our understanding of these traits in pterosaurs.

Cosesaurus fibers from posterior forelimbs. Image by Pierre Ellenberger (1993).

Figure 4. Cosesaurus fibers from posterior forelimbs. Image by Paul Ellenberger (1993). In his quest to interpret Cosesaurus as more birdy, Ellenberger flipped the hand over so that digit 4 became his digit 2. His sternal keel is actually the quadrant-shaped coracoid stem. His broad coracoids is actually one large sternum becoming integrated into a new structure, the sternal complex.

Cosesaurus truly is the Archaeopteryx of pterosaurs, bridging the gap between lizardy forms like Huehuecuetzpalli and the flying pterosaurs. I’m not the only ones seeing these structures. Dr. Paul Ellenberger saw them a decade earlier.

Cosesaurus hind limb with fibers and uropatagia. Image by Pierre Ellenberger (1993).

Figure 5. Cosesaurus hind limb with fibers and uropatagia. Image by Paul Ellenberger (1993).

A minor challenge
It would be nice if someone from the next generation of pterosaur workers would get on a plane to Barcelona and take a good look at this “Archaeopteryx of pterosaurs.” Since Science is built on testing observations, it’s just a shame that no one else in the last twenty years, other than yours truly, has confirmed Ellenberger’s key and important observations.

Of course, this would upset all sorts of paradigms and traditions if done.

Current interpretation of Cosesaurus.

Figure 6. Current interpretation of Cosesaurus with soft tissues in black. Rostral crest omitted here.  This is no ordinary macrocnemid. By any measure, this is the “Archaeopteryx” of pterosaurs and needs to be recognized as such. The pes matches narrow gauge, digitigrade and occasionally bipedal Rotodactylus tracks.

References
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.

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

A Closer Look at the Sordes “Uropatagium”

Uropatagium of Sordes according to Sharov 1971 and Unwin/Bakhurina 1994.

Figure 1. Uropatagium of Sordes according to Sharov 1971 and Unwin/Bakhurina 1994.

Sharov 1971
In 1971 Alexander Sharov described and illustrated the holotype of Sordes pilosus, a Jurassic pterosaur with extensive soft tissue preservation (Fig. 1). Sharov (1971) illustrated a uropatagium spanning the hind limbs and not attached to the tail which was angled off to the left.

Unwin and Bakhurina 1994
Twenty-three years later, Drs. David Unwin and Natasha Bakurina (1994) reported on the fibers embedded in the uropatagium of Sordes, which they described as attached to and controlled by the medially-directed fifth toe. Unfortunately since then another pterosaur with the same sort of uropatagium has not been found. The cartoonish drawing presented by Unwin and Bakhurina (1994) was a disappointment in view of the Sagan Standard, “Extraordinary claims require extraordinary evidence.”

Peters 2002
Peters (2002) noticed stratification beyond and in line with the proposed trailing edge membranes of earlier workers, and also noted that the right wing preserved a narrow-aft-of the elbow configuration, contra earlier reports. Noting the medial overlapping of membranes between the ankles, Peters (2000) suggested that twin uropatagia may have slightly overlapped one another. This turned out to be a mistake (see below).

Problems
For several decades paleontologists have been perplexed by the concept of a membrane spanning and binding the hind limbs, wondering if the cloaca opened above it or below it, wondering how such a morphology could have evolved, wondering how the hind limbs could have extended laterally with the tension of the membrane constantly pulling them medially. They wondered if the the tail had become detached form the midline of the uropatagium, which had an apparent V-shaped notch midway between the ankles.

Acceptance
Despite these questions and misgivings, the concept of the “single uropatagium” has remained firmly in place and widely accepted to the present day. This has become the traditional hypothesis. You can see recent illustrations of just such a uropatagium  hereherehere and a description by Dr. David Hone, “On the ground the ‘rhamphorhynchoids’ were probably pretty poor. Their large rear membrane would have shackled their hindlegs together making walking difficult, and the shape of their hips and upper legs meant that could only really sprawl and not walk upright.”

Elsewhere? No.
The big problem is, no other pterosaur has a uropatagium. All other specimens that preserve anything like it preserve paired uropatagia, shallower membranes extending behind each hind limb to the tail, with little to no membrane aft of the ankle and no direct connection to pedal digit 5. The pterosaur precursor, Sharovipteryx also had distinct paired uropatagia.

So what’s going on back there in Sordes?

The paired uropatagia and displaced wing membrane in the holotype of Sordes pilosus.

Figure 2. Click to enlarge and see the rollover image. The paired uropatagia and displaced wing membrane in the holotype of Sordes pilosus.

More Detail
Earlier we looked at the myth of the Sordes uropatagium. Here more detail is offered. The apparent membrane lateral to the left tibia, (directed a little above the ankle actually) is bordered by the displaced and otherwise missing ulna. The ulna is attached to the similarly displaced proximal portion of the left wing membrane, complete with aktinofibrils. Note: the membrane is quite narrow. The wing membrane extends beneath the left ankle, folds between the ankles and the torn tip continues toward the right fifth toe. A small portion of the torn wing membrane appears above the right foot. You can see the in situ specimen in closeup here. Earlier workers assumed that only the margin of the uropatagium was preserved because nothing is found more proximal to the body. Here, what you see is what you get.

Note the continuity of the membrane beneath the left tibia and tail. Note the doubling of the membrane, like a folded, crushed ribbon, creating the illusion of a medial angle between the ankles. Note the presence of aktinofibrils, which otherwise are found only on the wing. Note the pale borders of the actual paired uropatagia behind each knee — as in other pterosaurs and basal fenestrasaurs. Note pedal digit 5 was beneath the metatarsus.

Jumbles of hair lateral to the left ankle have no “core” and no certain origin, but may have come from the left anterior femur along with the drifting of the left ulna and radius and other hairs lateral to the left knee (which has a patella).

A Taphonomic Coincidence
By coincidence the ulna was oriented toward the ankle. By coincidence the membrane folded like a ribbon between the ankles.

The Value of DGS (Digital Graphic Segregation) in Testing Observations
It has often been said that the DGS (aka: Photoshop) method is intrinsically inferior to seeing the specimen first-hand. Well, apparently not in Sordes, nor in Jeholopterus, the IVPP embryo and several other pterosaurs and other reptiles, like Vancleavea in which either more detail was uncovered without seeing the actual fossil and subsequent testing failed to confirm original findings.

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
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277–301.
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].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

wiki/Sordes