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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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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).

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).

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.

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 1923. Anurognathus 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.

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.

Pterosaur Femur Time

Today we’ll take a look at the pterosaur femur, how it evolved and it’s range of motion in various pterosaurs.

Traditional Views of Basal Pterosaurs
Dr. Mark Witton reported, “… the orientation of the femoral head in basal pterosaurs means that the femur is projected forward, upward and laterally from the acetabulum, thereby causing the sprawling gait for the hindlimbs that acted in concert with the relatively short metacarpals to bring the bodies of these pterosaurs close to any surface they happened to be climbing over.”

Dr. Dave Hone reported, “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.” 

Let’s See What the Fossils Tell Us
Contra the above assertions, the fossils tell us just the opposite. Basal pterosaurs, like Austriadactylus and Eudimorphodon, had a right angle femoral head, as in dinosaurs (Figs. 1 and 2) by convergence. Derived pterosaurs, like Pteranodon and Anhanguera, had a much more obliquely angled femoral head (Fig. 3). The false notion of a “large rear membrane” that purportedly shackled the hind limbs mentioned by Dr. Hone (above) was dealt with earlier here.

Figure 1. Eudimorphodon ranzii femur in medial view, the head is circular because it is pointed toward the Z axis, at right angles to the plane of the matrix and the rest of the femur.

Figure 2. Femur of Eudimorphodon cromptonellus illustrating the right angle femoral head. This tiny specimen may be juvenile, hence the incomplete ossification at each end. When the axes of the femoral neck and laterally-oriented acetabulum lined up, an upright configuration was produced.

Figure 3. Derived pterosaur femur samples. Above, Pteranodon. Below, Anhanguera. Note the oblique angle of the femoral head. When the axes of the femoral neck and laterally-oriented acetabulum lined up in these pterosaurs, a sprawling configuration was produced.

Range of Motion
The range of motion in a pterosaur femur has been of some interest (Padian 1983; Wellnhofer 1988, 1991), impacting the quadrupedal/bipedal debate, among other topics. The discovery of uncrushed pterosaurs has been helpful, but those can’t discount the fossil record of crushed pterosaurs. Preservation in various angles and exposures paints a complete picture confirmed by comparing several sisters.

Padian (1983) proposed that pterosaurs tucked their hind limbs into the body while flying. While possible in basal pterosaurs, and likely while resting, such a configuration would have proven difficult in Anhanguera and Pteranodon with their sprawling femora. Plus reducing the distance between the femur and tibia in flight would have made the uropatagia disappear at a time when they would have been most useful. A more recent hypothesis (Peters 2002) proposed a more widespread femur acting as a horizontal stabilizer, a second wing (Fig. 5), as in the pterosaur sister Sharovipteryx. After all, lizards like Draco take to the air with outspread limbs and pterosaurs were flying lizards.

The Example of Austriadactylus
Austriadactylus was another basal pterosaur with a right angle femoral head (Fig. 4). Seen in various views it becomes clear that an upright stance with knees slightly beyond the ankles would have been appropriate given the shapes of the various elements. Contra Witton’s assertions (see above), Austriadactylus was not forced to crouch close to any surface it happened to be climbing over.

Figure 4. Austriadactylus femur. Range of motion. The foot was rotated posteriorly out of the airstream. The toes were likely webbed in all pterosaurs. When spread the webbed foot turned into a sail with lateral lift, helping to keep the knee extended even while facing the airstream.

Potential Problems with a Right Angle Femoral Head
While a derived sprawling femur would have had no problem assuming an outstretched flying configuration, I always wondered how a primitive right angle femur would handle it. Seemingly an inverted V-shape would have been all a basal pterosaur could muster. After closer examination (Fig. 4) that turned out to be true, but to less of an extent than I thought earlier. The femur could not rise to the horizontal, but it could come to within 20 degrees. The fact that the femoral head was more spherical in basal pterosaurs enabled this.

Lift from the Pelvis?
In Sharovipteryx and most pterosaurs the ilium does not rise much above the acetabulum. However in Longisquama and basal pterosaurs the anterior and posterior processes of the ilium rise as much as 45 degrees to the horizon or 90 degrees to each other (Fig. 4). Such a pelvis raises the torso and tail, which is ideal for bipedal leaping, as in Longisquama and living lemurs. Not so great though, to have an upright tail while flying. However, such an upright ilium also provides the leverage for the thigh muscles to lift (abduct) the hind limbs for flight. Later pterosaurs evidently did not need so much leverage with sprawling femora more aerodynamically shaped to provide their own lift in the airstream.

Figure 5. Arthurdactylus in dorsal view while flying. Note the sprawling hind limbs acting like horizontal stabilizers.

More About Derived Pterosaurs
Dr. Hone also reported, “The pterodactyloids had no such problems, as can be seen by their extensive fossil record of footprints. They had split their rear membrane in two freeing the legs which were brought under the body to allow them to walk far more effectively than their predecessors.” Let’s put more data on these assertions. While true that the feet were brought under the body (as in ALL pterosaurs, see Fig. 4), the knees in Pteranodon were actually configured further laterally than in basal pterosaurs. No problem. As you can see by the illustration below (Fig. 6), based on a 3D reconstruction of a complete skeleton, no matter the sprawl of the knees, as long as the knees were bent at right angles and the knees were below the plane of the acetabulum the feet remained beneath the body. This is simple engineering and standard operating procedure for all pterosaurs.

Figure 6. Standing Pteranodon. Note the sprawling femora do not hinder the bipdal stance. And, yes, Pteranodon likely placed its hands on the ground while walking, but so far anterior they could provide no forward thrust, only support.

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
Kellner AWA and Tomida Y 2000. Description of a New Species of Anhangueridae (Pterodactyloidea) with Comments on the Pterosaur Fauna from the Santana formation (Aptian-Albian), Northeastern Brazil. National Science Museum, Tokyo, Monographs, 17: 1-135.
Jenkins FA Jr, Shubin NH, Gatesy SM and Padian K 1999. A primitive pterosaur of Late Triassic age from Greenland. Journal of the Society of Vertebrate Paleontology 19(3): 56A.
Jenkins FA Jr, Shubin NH, Gatesy SM and Padian K 1999. A diminutive pterosaur (Pterosauria: Eudimorphodontidae) from the Greenlandic Triassic. Bulletin of the Museum of Comparative Zoology, Harvard University 155(9): 487-506.
Padian K 1983. A functional analysis of flying and walking in pterosaurs. Paleobiology 9:218.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Wellnhofer P 1988. Terrestrial locomotion in pterosaurs. Historical Biology 1: 3.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. (Salamander Books, London).
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

wiki/Eudimorphodon

A New Wing Shape for Pterosaurs?

A recent paper by Palmer and Dyke (2011) revised the wing shape and orientation of pterosaurs based on mechanical and aerodynamic constraints. Unfortunately they got the anatomy wrong in several instances spelled out below. Those mistakes affected their results.

Once Again, the Deep Wing Paradigm Has Been Promoted as True
Palmer and Dyke (2011) reported, “We know that the margin of the pterosaur wing membrane was unconstrained posteriorly and attached distally to the ankle and body.” Without critical examination, they accepted and cited Elgin, Hone and Frey (2011) and Kellner et al. (2010) which were critically reexamined here and here.

Figure 1. The Palmer and Dyke model is on the right. The Stromer/Schaller/Peters model is on the left.

Palmer and Dyke (2011) Made Several Mistakes
In airplanes, birds and bats the CG (center of gravity) is at the wing spar root (between the shoulder joints). Presumably the same was true of pterosaurs. Move the elbow back to where it belongs and add flesh to the thighs based on pelvis length to add more mass aft of the CG. Permit the aktinofibrils to make a spoon-shaped wingtip, as they do in fossils. Split the uropatagium into uropatagia (as in Sharovipteryx and Sordes) and move the femur laterally to create an airplane-like horizontal stabilizer. No pterosaur is preserved with wing membranes attached to the ankles. Rather the membranes always are directed to the elbow with a small fuselage fillet attached to the femur.

The great majority of pterosaur workers, including the two anonymous referees who green-lighted this paper, follow the Palmer and Dyke (2011) model (on the right), despite its falsehoods and problems. The heretical view (on the left) follows the fossil evidence strictly. If anyone can produce and trace a specimen with a deep wing membrane attached at the ankle, I’ll marry their sister.

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 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Kellner AWA, Wang X, Tischlinger H, Campos DA, Hone DWE and Meng X 2010. The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane. Proc Royal Soc B 277: 321–329
Palmer C and Dyke G 2011. Constraints on the wing morphology of pterosaurs. Proceedings of the Royal Society B. published online 28 September 2011.
doi: 10.1098/rspb.2011.1529
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Schaller D 1985. Wing Evolution. In: Hecht M, Ostrom JH, Viohl G and Wellnhofer P, eds, The Beginning of Birds. Proceedings of the International Archaeopteryx Conference, Eichstätt 1984, (Freundes Jura Museum, Eichstätt), pp. 333–348.
Stromer E 1910. Bemerkungen zur Rekonstruktion eines Flugsaurier-Skelettes. Monatsberichte der deutschen Geologischen Gesellschaft 62, 85–91.
reptileevolution.com/pterosaur-wings.htm

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.

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.

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  Coelurosauravus, Weigeltisaurus 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