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.

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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

Another Really Tiny Pterosaur: BMNH 42736

The smallest known pterosaur B St 1967 I 276 (No. 6 of Wellnhofer 1970 ) was discussed earlier. Today we get to meet maybe the second smallest pterosaur, Pterodactylus meyeri BMNH 42736 (Munster 1842, Fig. 1) is the same size as No. 6, but had several distinct traits (Fig. 2). I ran across the BMNH specimen in Unwin’s (2006) The Pterosaurs From Deep Time book on page 151. Dr. Unwin considered the specimen a “flapling” (= newly hatched pterosaur able to fly) with a wingspan of 17 cm, so that is the reconstructed scale (Fig. 3).

The Value of a Reconstruction
It’s a shame that modern workers don’t produce reconstructions of crushed pterosaurs anymore. There is so much to see (Figs. 2, 3), especially when one compares similar specimens. Many traits would go unnoticed if left crushed.

One of the world's smallest pterosaurs

Figure 1. One of the world's smallest pterosaurs, traced from Unwin (2006, p. 151). The feet of the "flapling" were not articulated and a certain amount of guesswork was applied to the idenfication of the pedal elements and their reconstruction. Note how the left radius and ulna are parallel to and beneath the elongated right scapula. The right coracoid is largely beneath the right humerus. The left hand and proximal wing finger are beneath the right hand. Soft tissue stains are highlighted in orange. The wing had a narrow chord at the elbow. Colorizing the bones is a result of employing DGS, digital graphic segregation.

Phylogenetic Nesting
Here the “flapling” nested between No. 6 and No. 12, two other tiny ornithocephalians (and former Pterodactylus) outside of the Pterodactylus lineage, at the base of the Germanodactylus clade. Conveniently (for those looking for transitional taxa) No. 6 was smaller and No. 12 was larger than the BMNH “flapling.”

Distinct from No. 6, the “flapling” had a deeper skull, more and smaller dorsal vertebrae and ribs, a longer scapula (almost touched the pelvis), a deeper and more fully fused pelvis and a larger sternal complex than either of its sisters. Considering the reconstructed differences in quadrate elevation, jugal shape and pelvis dimensions (Fig. 2), you might think the “flapling” would have nested further apart from No. 6 and No. 12. These distinctions suggest that the “flapling” may have been at  the base of its own clade of currently unknown descendants.

The tiniest pterosaurs.

Figure 2. The tiniest pterosaurs. On the left, Unwin's "flapling" Pterodactylus meyeri BMNH 42736. On the right, B St 1967 I 276, No. 6, the former sole owner of the title.

Juvie or Adult?
If the BMNH tiny pterosaur was indeed a juvenile of a larger more established taxon, which one did it match up to? And if so, why did it nest with other tiny pterosaurs? No. The BMNH specimen was an adult. The many autapomorphies (= differences) in the “flapling” also follow a larger trend seen in other tiny pterosaurs: morphological innovation.

Full scale image of ginkgo leaf and the two smallest pterosaurs

Figure 3. Full scale image of ginkgo leaf and the two smallest pterosaurs to scale on a 72 dpi screen. Yes, these are tiny, but just look at the size of a hatchling on the far right, no bigger than a small fly.

Special Premaxillary Teeth
In the BMNH “flapling” we see more substantial anteriorly-directed medial teeth forming the tip of the premaxilla. Those two teeth evolve to become one in the rostral tip of Germanodactylus. That tooth is the only one retained in so-called “toothless” pterosaurs like Pteranodon and Nyctosaurus that have sharply tipped jaws.

Bigger Eggs?
A deeper pubis and pelvis in the BMNH specimen could have produced a larger egg. A stronger sternal complex and longer scapula could have made the “flapling” a more powerful flyer.

Soft Tissue Preservation
Despite a flipped mandible and poorly preserved feet, the “flapling” is otherwise well preserved and largely articulated. A soft tissue stain can be seen (overprinted in Fig. 1) that demonstrates a narrow chord at the elbow wing membrane construction.

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
Meyer H von 1842. Notes on labyrinthodonts and fossil reptiles, including a description of Belodon plieningeri, new gen. and sp. Neues Jahrbuch fur Mineralogie, Geologie und Palaontologie 1842, pp. 301-304.
Unwin D M 2006. 
The Pterosaurs From Deep Time. 347 pp. New York, Pi Press.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

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

What the Dark Wing Rhamphorhynchus Tells Us

When the “Darkwing” Specimen of Rhamphorhynchus (Goldfuss 1831, von Meyer 1846, Frey and Tischlinger 2002, JME SOS 4785) appeared, it looked like all of our arguments about wing shape in pterosaurs were finally over. And that’s how it was promoted. In this specimen (Fig. 1) the wing membrane is clearly delineated, layered and undoctored.

Figure 1. The darkwing specimen of Rhamphorhynchus. Top: in situ. Middle: Soft tissues highlighted. Bottom: Neck and forelimb reconnected to their natural positions.

First Take – The Traditional Hypothesis
Tischlinger and Frey (2002) made no attempt at restoring the broken, folded and mutilated pieces of the specimen, as shown above. Rather they interpreted the soft tissue behind the elbow (in orange above) as a continuation of the wing membrane despite the obvious differences in texture and the separate layers each appears on, while ignoring what would happen if the wing were extended into the flying position  (Fig. 1). Moreover there is a sharp right angle between the wing membrane and the schmootz lateral to the tibia, not the smooth curve predicted by the deep chord/attached to the ankle wing hypothesis.

Second Take – The Heretical Hypothesis
If you put this “Humpty”  back together again (which is ridiculously easy to do) and extend the wing into the flying position it becomes more than clear that the key portions of the wing membrane behind the elbow and wrist were not preserved/exposed. So it doesn’t tell us what the Zittel wing has told us for several decades. Posterior to the elbow the pterosaur wing had a narrow chord and was stretched between the elbow and wingtip with a small fuselage fillet extending back to the femur.

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
Elgin RA, Hone DWE and Frey E 2010. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica in press. doi: 10.4202/app.2009.0145
Goldfuss A 1831. Beiträge zur Kenntnis vershiedener Reptilien der Vorwelt. Nova Acta Academiae Leopoldinae Carolinae, Breslau and Bonn, 15: 61-128.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Tischlinger H and Frey E 2002. Ein Rhamphorhynchus (Pterosauria, Reptilia) mit ungewöhnlicher Flughauterhaltung aus dem Solnhofener Plattenkalk. Archaeopteryx, 20, 1-20.
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33.Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

wiki/Rhamphorhynchus

The Flat-Head Pterosaur

Part of a Private Collection Made Public
There is a tiny little anurognathid pterosaur in a private collection that Dr. S. Chris Bennett (2007) described as a small Anurognathus ammoni (Döderlain 1923). Here that specimen was found to nest next to Anurognathus, but it was neither conspecific nor congeneric with Anurognathus. It was distinct in morphology from flat head to tiny toe. It actually shares more characters with it phylogenetic predecessor,  Dendrorhynchoides (Ji and Ji 1998 ), including a very wide sternal complex and torso. While most pterosaurs had long pointed jaws and most anurognathid pterosaurs had a round, bubble-like skull, this particular anurognathid had the flattest, widest, most pancake-like skull of all. The eyeballs would have popped up above the skull outline, like a frog’s eyeballs. Figure 1 portrays both anurognathids to scale. The many differences are easy to see. Let’s run through them.

Figure 1. The flat-head pterosaur, a private specimen (on the left) attributed by Bennett (2007) to Anurognathus ammoni (on the right).

Figure 1. The flat-head pterosaur, a private specimen (on the left) attributed by Bennett (2007) to Anurognathus ammoni (on the right).

The Skull
The skull was described by Bennett (2007) as having an enormous orbit in the anterior half of the skull, little to no antorbital fenestra, and a broad set of parietals with widely spaced upper temporal fenestra among several other autapomorphies. (You can view those illusory interpretations here). No sister taxa have these traits. Nevertheless, this false and frankly, goofy to monstrous reconstruction has become widely accepted. Such a reconstruction replaces the large air-filled antorbital fenestra of all other pterosaurs with gel-filled eyeballs. Such a reconstruction moves the eyeballs into the anterior half of the skull, the opposite of all other pterosaurs. Bennett (2007) mistook the curved and dentally subdivided maxilla for a giant sclerotic ring preserved on edge, which no other crushed specimen of any tetrapod ever does. Bennett (2007) was unable to segregate the layers of bones so reconstructed a wide, flat parietal, the opposite of all other pterosaurs. Here DGS (digital graphic segregation) was able to delineate all the skull bones recovering identical left and right elements that resemble those of sister taxa and produce a reconstruction in line with sisters, rather than completely different as in the Bennett (2007) reconstruction (see both here).

At left the traditional Bennett (2007) interpretation. On the right, interpretation based on finding and tracing paired bones.

Figure 2. At left the traditional Bennett (2007) interpretation. On the right, interpretation based on finding and tracing paired bones.

The Post-Crania
The rest of the skeleton was much more typical of anurognathid pterosaurs. The cervical series was relatively longer than in Anurognathus. The torso was not as wide as in Dendrorhynchoides and the dorsal ribs were more gracile. The caudals were greatly reduced. The sternal complex was not quite as wide. The pteroid was smaller. Bennett (2007) determined that manual phalanx 4.4 was missing, but it is largely buried. The distal portion reappears at the pelvis and all sister taxa have four long wing phalanges. Pedal digit 2 is not the longest. The proximal pedal phalanges had more typical proportions than the short ones in Dendrorhynchoides.

The Flathead Anurognathid

Figure 3. The SMNS anurognathus as reconstructed in various views. Black circle is hypothetical egg.

Why The Wide Face?
Obviously the wide flat skull gave the private specimen some sort of competitive advantage. Certainly the wider gape captured more tiny insects. The disc-like shape, like a flying saucer, may have been raised and lowered in the airstream to affect the flightpath and such a shape reduced aerodynamic drag while streamlined in the neutral position.

Think About the Size of the Egg!
With such a tiny pelvic opening, the egg of the private specimen would have been very tiny, on the order of 3-4 mm in diameter. The hatchling would have stood one-eighth as tall as the 6 cm adult or less than 8 mm in height (possibly taller if the egg was elongated).  Such a fly-sized pterosaur risked desiccation if it flew in dry air, so it may have scurried about in damp leaf litter snatching insects on the ground as a juvenile.

Click here for more information and images.

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
Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.
Bennett SC 2008. Morphological evolution of the wing of pterosaurs: myology and function. Zitteliana B28: 127-141.
Döderlain L 1923Anurognathus ammoni, ein neuer Flugsaurier. Sitzungsberichte der Königlich Bayerischen Akademie der Wissenschaten, zu München, Mathematischen-physikalischen Klasse: 117-164.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Ji S-A and Ji Q 1998. A New Fossil Pterosaur (Rhamphorhynchoidea) from Liaoning. Jiangsu Geology 4: 199-206.
Peters D 2001. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15:277–301.
wiki/Anurognathus

Another Use for Pterosaur Tale Vanes

Where are Pterosaur Tail Vanes Found?
Basal pterosaurs are often illustrated with tail vanes, but they are not found on many basal pterosaurs. Soft tissue preservation is rare. The Campylognathoides/Rhamphorhynchus clade had the most prominent tail vanes. Various Dorygnathus may have had something like a vane. It’s never clear. Sordes had some sort of tail expansion and Pterorhynchus did not have a single vane, per se, but several very short ones along the length. The tail vane seems to have coalesced from several smaller vanes, which, in turn, may have developed from specialized ptero-hairs seen on the tail of Cosesaurus.

Tail vane animation on the C5 specimen of Campylognathoides.

Figure 1. Click to animate. Tail vane animation on the C5 specimen of Campylognathoides zitteli.

Tail Vane Usage
The tail vane has typically been considered a steering mechanism, but airplanes don’t steer with their tail (vertical stabilizer). That just produces a skid and lots of drag. To initiate a turn airplanes, birds and bats roll into a bank.  Presumably pterosaurs did likewise. The tail vane would have worked like feathers on an arrow shaft, keeping the back of the tail in line with the line of least drag, in line with the body at all times, and all without effort.

Correlations
You might note that the most prominent tail vanes are also found in the clade with the longest wings in relation to their body size. In Campylognathoides and Rhamphorhynchus the wing tips extend far above their head. The tail itself was stiff, able to rise and fall tilting at its base. The same was true of the wings. They were stiff and able to fold and unfold at the metatarsophalangeal joint. Those are similar actions as seen from the side. That got me thinking.

The Metronome Hypothesis
What if the tail rose and fell like a metronome? The wings could open and fold in counterpoint. Together the three elements might have produced a secondary sexual behavior that attracted mates… or was just a way to relax.

Pure speculation.  Enjoy the animation.

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.