SVP abstracts – Ornithocheirid hip range of motion (ROM)

Griffin et al. 2019 report on their study
of the Coloborhynchus (Figs. 3) pelvis during a hypothetical launch. We looked at this issue earlier here following publication of Witton and Habib 2010.

From the abstract:
“Pterosauria includes the largest animals to achieve powered flight. How medium to large-sized pterosaurs were able to launch into the air is a matter of debate.”

Oh, no. Not this invalid hypothesis again. Griffin et al. believe that giant azhdarchids could fly. They could not. Look how short their wings are compared to volant giant seabirds, pteranodontids and ornithocheirids (Fig. 1).

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Griffin et al. continue:
“Birds employ their legs to accelerate their bodies into the air, but the difficulties large birds face in becoming airborne suggests take-off may limit the maximum size of birds. It has been suggested that pterosaurs employed their fore and hindlimbs in take-off, the so-called quadrupedal launch mechanism, overcoming the size constraint.”

That suggestion is not documented in the fossil record. Quad launch is not only dangerous, it is untenable and clearly inferior to using both the wings and legs to produce massive amounts of thrust as large volant birds do. Flightlessness in man-sized and smaller birds made possible flightless giant birds. The same was true for pterosaurs. All the giant pterosaurs had clipped wings (vestigial distal phalanges).

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 2. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Griffin et al. continue
“Range of motion (ROM) studies are a common way of determining the viability of hypothetical poses in extinct animals. Here we use ROM mapping of the hip joint of a mid-sized pterosaur, Coloborhynchus (SMNK PAL 1133. Fig. 2) to test whether the joint surfaces of the acetabulum and femur were capable of achieving a bipedal and/or a quadrupedal stance during the range of motion required for take-off.” 

Figure 2. GIF animation showing stages in the bipedal take off of Coloborhynchus. Please imagine the wings talking their first mighty flap at the moment of takeoff, relieving the hind limbs from most of the stress.

Figure 3. GIF animation showing stages in the bipedal take off of Coloborhynchus. Please imagine the wings talking their first mighty flap at the moment of takeoff, relieving the hind limbs from most of the stress. In the invalid quadrupdal pose, note the proximal wing finger makes an impression, which never happens in pterosaur tracks.

Griffin et al. continue:
“Using the software programs Maya and MATLAB, possible intersections and orientations between different bones of the hip joint were identified and coded as viable or unviable. Osteological ROM mapping reveals a quadrupedal stance is more likely in launch, with maximum crouch during quadrupedal launch and flight positions being possible.”

See, they had a preconceived bias and did not comparatively test the bipedal configuration. Remember, in the bipedal pose the wings are ready to provide thrust BEFORE the legs launch the pterosaur into the air (Fig. 3). So the legs are not working alone. By contrast in the quad launch scenario, the wings are not unfolded, and not raised above the shoulders when the pterosaur is at the apogee of whatever feeble take-off abducting the antebrachium can provide (Fig. 2).

Figure 1. The as yet undescribed SMNS PAL 1136 specimen is much larger than comparable bones in the new specimen, MPSC R 1221.

Figure 4. The as yet undescribed SMNS PAL 1136 specimen is much larger than comparable bones in the new specimen, MPSC R 1221. This is a resting pose. When walking or preparing to flap the wings would have to rise off the substrate. This sort of giant-winged, small footed, volant creature rarely landed, IMHO.

Griffin et al. continue:
“However, it is important to consider not just osteological ROM but also the effects of soft tissues. ROM simulations can approximate the effect of different soft tissue such as ligamentous constraints and joint cartilage. We find that the required orientation for bipedal launch was not possible without the presence of cartilage. In order to achieve a bipedal stance in this specimen, a minimum of 3 mm of cartilage is required to sufficiently increase the ROM.”

3mm. That’s not very much, and well within the range of possibilities for a large pterosaur. I look forward to seeing their bipedal launch configuration. Having dealt with pterosaur workers cheating morphology to support their bias (e.g. Elgin, Hone and Frey 2011), I’m always suspicious  based on reputation and history.

“A ROM study that included ligaments in addition to cartilage reduced the available viable orientations. This ROM generated in this study does not rule out the possibility of a quadrupedal launch in pterosaurs, and provide greater support for the quadrupedal rather than the bipedal launch hypothesis.”

These authors mistakenly believe that pterosaurs were archosaurs. Testing reveals they are lepidosaurs (Peters 2007). Ligament issues need to based on lepidosaur pelves and hind limbs, not archosaur. Did the authors sprawl the femora, matching femoral head axis to pelvic socket axis? Having built several pterosaur skeletons, I can tell you, the bipedal stance works best. The ROM at the hips is the LEAST of their worries if they are trying to launch a pterosaur with ventrally folded wings.


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
Griffin BW et al. 2019.
Simulated range of motion mapping of different hip postures during launch of a medium-sized ornithocheirid pterosaur. Journal of Vertebrate Paleontology 2019.
Peters D 2007.The origin and radiation of the Pterosauria.Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27
Witton MP and Habib MB 2010. On the Size and Flight Diversity of Giant Pterosaurs, the Use of Birds as Pterosaur Analogues and Comments on Pterosaur Flightlessness. PLoS ONE 5(11): e13982. https://doi.org/10.1371/journal.pone.0013982

Flugsaurier 2018: Web-footed little pterosaur MB.R.3531

Flugsaurier 2018 part 4
Since the purpose of the symposium is increase understanding of pterosaurs, I hope this small contribution helps.

Figure 1. Aurorazhdarcho primordial and the smaller Aurorazhdarcho micronyx to scale.

Figure 1. Aurorazhdarcho primordial and the smaller Aurorazhdarcho micronyx to scale.

Habib and Pittman 2018
bring us a rarely studied Berlin pterosaur, MB.R.3531 (Fig. 1) originally named Pterodactylus micronyx, then Aurorazhdarcho micronyx. This specimen nests with other wading pterosaurs, Aurorazhdarcho, Eopteranodon and Eoazhdarcho forming  a clade overlooked by other workers, at the transition between germanodactylids and pteranodontids, not related to azhdarchids.

FIgure 1. Reconstruction of MB.R.3531, nesting with Eoazhdarcho, Eopteranodon and Aurorazhdarcho.

FIgure 1. Reconstruction of MB.R.3531, nesting with Eoazhdarcho, Eopteranodon and Aurorazhdarcho.

But phylogeny is not what interests Habib and Pittman.
They report, “We provide the description of an exceptionally well-preserved specimen of a juvenile aurorazhdarchid from the Jurassic of Germany which preserves details of the wing membrane and pedal webbing and use it to address mechanical questions regarding launch from water in small pterosaurs.” We can’t be sure it’s a juvenile because pterosaur juveniles are isometric copies of their parents and phylogenetic miniaturization often attends the genesis of new pterosaur clades.

This is a wading pterosaur, part of a clade of long-legged wading pterosaurs. It has webbed feet for wading, not for swimming. Wading birds don’t go in water deeper than they can wade in and they take to the air by flapping their wings and leaping. The MB.R. specimen was originally mistaken for Pterodactylus because it greatly resembled Pterodactylus, another clade of small to medium-sized waders leaving numerous webbed tracks. Also back then they had fewer pterosaurs to compare, other than Pterodactylus.

Habib and Pittman don’t buy into the lepidosaur origin of pterosaurs.
They report, “The latest range of motion estimates for the pterosaur hind limb (Manafzadeh and Padian, 2018) suggest that the hind limbs in pterosaurs had more limited abduction than previously modeled and that the hindlimbs operated primarily in a vertical plane.” We invalidated that claim earlier using phylogeny (pterosaurs are more closely related to squamates than to birds). Dozens of pterosaur fossils show the hind limbs spread and form horizontal stabilizers during flight (Fig. 3). That’s when the webbed feet become useful, as twin vertical stabilizers. Webbed feet are primitive for pterosaurs and are found in pterosaur outgroups, like Sharovipteryx.

Figure 3. Click to animate. The Vienna specimen of Pterodactylus (wings folded). Animation opens the wings and legs to reveal the true shape of pterosaur wings, stretched between the elbow and wingtip with a short fuselage fillet extending from elbow to mid femur. The feet act like vertical stabilizers.

Habib and Pittman insist
“We estimate that MB.R.3531 was capable of taking off from the water surface with a single escape push (under the most liberal model values) or with 1-2 follow-up bounding phases (under the most conservative model values), with the majority of the takeoff energy expended on the initial escape phase. The added propulsive area of the pedal webbing had a notable effect on the overall launch performance, increasing estimated propulsive accelerations by over 20% and reducing the number of required propulsive bounding phases.” There’s no need for bounding for floating pterosaurs. They can simply stretch out and flap their wings like pelicans do (Fig. 4) while they frantically kick their feet. In any case, the MB.R. specimen is a wader, so the problem is moot. We looked at water-launch problems in pterosaurs earlier here, here and here.

Pelican take-off sequence from water.

Figure 4. Pelican take-off sequence from water. Click to enlarge.

Habib and Pittman conclude:
“The exact values and kinematic results should be taken with caution, given the large number of values that had to be broadly estimated or assumed.” One wonders why these authors don’t just let their hypothesis drop in favor of one that employs the more than adequate thrust generating power of pterosaur wings together with frantically paddling feet.

References
Bennett C 2013. New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift, 87, 269–289.
Habib M. and Cunningham J 2010. Capacity for Water Launch in Anhanguera and Quetzalcoatlus. Acta Geoscientica Sinica, 31, Supp.1, 24–25.
Habib M and Pittman M 2018. An “old” specimen of Aurorazhdarcho micronyx with exceptional preservation and implications for the mechanical function of webbed
feet in pterosaurs. Flugsaurier 2018: The 6th International Symposium on Pterosaurs. Los Angeles, USA. Abstracts: 41–43.
Manafzadeh AR and Padian K 2018. ROM mapping of ligamentous constraints on avian hip mobility: implications for extinct ornithodirans. Proceedings of the Royal Society B, 285(1879).

“Why we think giant pterosaurs could fly” (…NOT!)

Yesterday the Dinosaur Mailing List
linked a MarkWitton.com blogspot.com post titled, Why we think giant pterosaurs could fly.” It’s worthwhile looking (once again) at the arguments Dr. Witton most recently put forth to test them against the evidence presented by pterosaurs here at PterosaurHereseies. After all, it’s not fair to dredge up arguments Dr. Witton may have long ago abandoned. Alas, Dr. Witton is holding fast to his old arguments and pet hypotheses, many of which paint a false picture of pterosaur biology and behavior, based on evidence to the contrary (see below).

Dr. Witton precedes his arguments
with the admission that, “Giant azhdarchids are invariably known from scant remains, sometimes a handful of fragments representing bones from across the skeleton or, in the case of Quetzalcoatlus northropi, an incomplete left wing.” We looked at Q. northropi wing elements earlier here (Fig. 1). They are indeed scant, but nevertheless, impressive.

Figure 1. Quetzalcoatlus specimens to scale.

Figure 1. Quetzalcoatlus specimens to scale. Q. sp. is also enlarged to the humerus length of Q. northropi. Gray zones are hypothetical and/or restored. Reduction of the wing, even in the smaller species, argues against flight in giant azhdarchid pterosaurs, as it does in much smaller flightless pterosaurs.

 

Dr. Witton reports,
…just a few bones can betray volant habits. It’s evident that even the largest pterosaurs bore wing anatomy comparable to their smaller, incontrovertibly flightworthy relatives. The huge deltopectoral crest…is a clear correlate for powered flight in giant species.” 

Unfortunately
Dr. Witton does not acknowledge the presence of any flightless pterosaurs (taxon exclusion). Flightless pterosaurs could test Dr. Witton’s ‘dp crest clear correlate’ hypothesis. Three flightless pterosaurs have been reported here based on their relatively short wings: SoS2428, PIN 2585-4, and Alcione (Fig. 2). Notably, all three have an unreduced deltopectoral crest.

Figure 2. Flightless pterosaurs, SOS24248, PIN2584-4, Alcione, to scale.

Figure 2. Flightless pterosaurs, SOS24248, PIN2584-4, and Alcione, to scale. Reducing the span of the wing is the easiest and most common way to become flightless in pterosaurs.

Wing length vs body size
provides the best argument for flightlessness in the case of SoS2428 (Fig. 3), itself a pre-azhdarchid. The same argument works for the other two flightless pterosaurs when comparisons to flighted sisters are presented.

Lateral, ventral and dorsal views of SoS 2428

Figure 3. Lateral, ventral and dorsal views of SoS 2428 alongside No. 42, a volant sister taxon. In dorsal view it becomes very apparent which one would be flightless.

Arthurdactylus

Figure 4. Arthurdactylus in dorsal view. Note the rather small deltopectoral crest in this taxon.

It’s a good time to remember
that hatchling pterosaurs had adult proportions. They were able to fly shortly after hatching. This also means that small to tiny pterosaurs had wing/body ratios comparable to those of the largest incontrovertibly flying pterosaurs, the ornithocheirids (Fig. 4) and pteranodontids. Notably, the deltopectoral crest of the ornithocheirid, Arthurdactylus, is relatively smaller than one would predict using Witton’s hypothesis, and quite variable in other members of this clade.

Dr. Witton reports,
“for large azhdarchids: their functional morphology and trackways show strong terrestrial abilities and they probably spent a lot of time grounded, only flying when harassed, or wanting to move far and fast. Indeed, in all likelihood giant pterosaurs couldn’t launch every few moments.”

Unfortunately
Dr. Witton does not consider the possibility that large azhdarchids could have employed wing thrust to hasten their getaways on the ground, like many large birds do (Fig. 5).

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 5. Quetzalcoatlus running like a lizard prior to takeoff. Click to animate.

Witton and Habib 2010
used software designed to model bird flight to predict that giant azhdarchids could fly faster than 90 kph and were easily able to sustain long distance glides.

Witton reports: “The key to everything: quad launch”
and provided a helpful illustration (Fig. 6) to show the moment of takeoff. Remember, in pterosaurs the wing finger never makes an imprint, so the three tiny free fingers must bear some multiple of the entire weight of the pterosaur at the moment of lift-off, then the ventrally-oriented wing finger must circle around to provide at least one upward lift and one downward flap before the otherwise inevitable crash. Not even a heavily muscled kangaroo can lift itself to such a height on the first leap. Not even a body builder can perform such a push-up… but a tiny vampire bat can, and does so routinely.

Figure 6. In the 'quad launch' hypothesis, for which there is currently no fossil imprint evidence, the pterosaur does a sort of leaping push-up using its tiny free fingers to bear a multiple of its entire weight during the acceleration, without flapping, to takeoff speed.

Figure 6. In the ‘quad launch’ hypothesis, for which there is currently no fossil imprint evidence, the pterosaur does a sort of leaping push-up using its tiny free fingers to bear some multiple of its entire weight during the acceleration, without flapping, to takeoff speed. Then the dangerous part begins. The pterosaur has to swing its wings up and down to creat aerial thrust before crashing (see figs. 7, 8). The short humerus provides little leverage to do this. Among tetrapods, only tiny highly derived bats are able to succeed with this sort of takeoff scenario. All other pterosaurs flap first, then fly.

What happens
if pterosaurs don’t make altitude every time they attempt a launch? (Fig. 7) Calamity (Fig. 8). There is no room for error, no evolutionary path to perfection, even if possible. Can one enhanced pushup provide the necessary airspeed and altitude without wing assistance? Witton and Habib think so? Look what those giant wings have to do before contributing to thrust and lift. Much better to get those wing providing thrust and lift at the moment of takeoff, rather than waiting until, perhaps, too late.

Successful Pteranodon wing launch based on work by Habib (2008).

Figure 7. Successful Pteranodon wing launch based on work by Habib (2008). Best case scenario.

 

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 8. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Successful heretical bird-style Pteranodon wing launch

Figure 9. Successful heretical bird-style Pteranodon wing launch in which the hind limbs produce far less initial thrust because the first downstroke of the already upraised wing provides the necessary thrust for takeoff in the manner of birds. This assumes a standing start and not a running start in the manner of lizards. Note three wing beats take place in the same space and time that only one wing beat takes place in the Habib/Molnar model.

 

re: the pelvis
Witton reports, “The avian skeleton has two large girdles for limb muscles: an enlarged shoulder and chest region for flight muscles, and an enhanced pelvic region to anchor those powerful hindlimb launch muscles. Pterosaurs, in contrast, have only one large limb girdle – their shoulders, making this the de facto likely candidate for powering their launch cycles.”

Standing Pteranodon

Figure 10 Standing Pteranodon (the Triebold specimen). Note the robust and extended pelvis supported by at least nine sacrals.

It may be traditional to discount the pelvic region
of pterosaurs, but in all cases, the pelvis is also enhanced (Fig. 10) with fused sacrals, prepubes and an anteriorly expanded ilium anchoring powerful, and under appreciated muscles.

Ignoring evidence that does not serve a pet hypothesis.
Witton ignores the hard evidence of bipedal pterosaur trackways, when he quotes Habib 2008, who “also notes that launch in living tetrapod fliers correlates to terrestrial gait: the number of limbs used to locomote on the ground is the same as the number used to take-off. Birds walk and launch with two legs, while bats walk and launch using all four. An extensive record of pterosaur trackways shows that pterosaurs were quadrupedal animals like bats, and it stands to reason that they also launched from four limbs: they would contrast with our living fliers if they had to shift gaits to take off.” 

Witton calls the quad-launch
“the most efficient launch mechanism conceivable for a tetrapod,” ideal for such a strong humerus and such a weak femur. Julia Molnar produced a video of a quad launch.  You might remember that the Molnar pterosaur free fingers were incorrectly reduced (Fig. 11) and relocated to the dorsal (in flight) surface of the wing in order to get that big wing finger on the ground and ready to snap like a grasshopper’s hind limb. Yes, they cheated the anatomy to make their pet hypothesis work… and Dr. Witton warmly embraced, rather than pointing out its faults.

The so-called catapult mechanism in pterosaurs

Figure 11a. Left: The so-called catapult mechanism in pterosaurs. The fingers are in the wrong place and cheated small in order to let the wing finger make contact with the substrate – which never happens according to hundreds of pterosaur tracks. Right. The actual design of pterosaur (in this case Anhanguera/Santandactylus) fingers. Click to enlarge.

Errors in the Habib/Molnar reconstruction of the pterosaur manus

Figure 11b. Errors in the Habib/Molnar reconstruction of the pterosaur manus

 

The infamous animation by Molnar
(click to play YouTube video) apparently assumes a nearly weightless mass, a super powerful pushup, and a suspension of the moment of inertia required to drag that big pool stick of a wing finger around to the flying position after it has just been oriented ventrally to say nothing about the effects of drag while opening that less than aerodynamic wing membrane. Isn’t it better to completely extend that wing and set it in the upward position before launch?

Summary of points ignored by Dr. Witton

  1. The largest flying pterosaurs have the largest/longest wings
  2. Flightless pterosaurs do exist and they are identified by their short wings
  3. Flightless pterosaurs retain a large deltopectoral crest and continued flapping to provide thrust for fast getaways and threat displays
  4. The quad launch hypothesis was built on the false premise of wing finger contact with the substrate
  5. The quad launch is dangerous for its participant every time they perform it. Much better to generate wing thrust at the moment of takeoff, not some time later. Such takeoffs can be aborted or diverted without the danger of a crash landing.
  6. The quad launch hypothesis works well for small  bats, ankle high to a Dimorphodon (Fig. 12), which fly in a different fashion from other volant tetrapods, but this ability does not scale up well for giraffe-sized or other pterosaurs.
  7. Dr. Witton cherry-picks the data that fits his hypotheses and ignores data that invalidates the last few years of his work.
  8. Given the paucity of data at present for giant azhdarchids, it would have been appropriate to restore Q. northropi as flightless AND volant, and tell us where the dividing line would be if the missing bones were one way or the other, making comparisons to smaller azhdarchids and to other fully volant large pterosaurs, like ornithocheirids and pteranodontids.
  9. It would have been professional and appropriate for Dr. Witton to alert us to the (perhaps inadvertent) cheating Molnar and Habib did to their pterosaur manus (Fig. 11) before some rank amateur brought it to our attention, and not to adopt this bogus and untenable idea with such gusto (Fig. 6), perhaps out of friendship.
Figure 3. Dimorphodon and Desmodus (the vampire bat) compared in size. It's more difficult for larger, heavier creatures to leap, as the mass increases by the cube of the height. Size matters. And yes the tail attributed to Dinmorphodon, though not associated with the rest of the skeleton, was that long. Note the toes fall directly beneath the center of balance, the shoulder glenoid, on this pterosaur, And it would have been awkward to get down on all fours.

Figure 12. Dimorphodon and Desmodus (the vampire bat) compared in size. It’s more difficult for larger, heavier creatures to leap, as the mass increases by the cube of the height. Size matters.  Note the toes fall directly beneath the center of balance, the shoulder glenoid, on this pterosaur, And it would have been awkward to get down on all fours, especially with giant finger claws.

At what stage(s) did azhdarchids lose the ability to fly?
If we just look at wing length (reduction of distal elements) then this clade appears to have become flightless at least twice (Fig. 13). In both instances that happens when the wing finger tip is no higher (when folded) than the dorsal rim of the dorsal vertebrae. And that happens the second time when azhdarchids double in size to standing over a meter tall. If valid, then the doubling and doubling in size of azhdarchids was possible because they gave up aerial pursuits in favor of a fully terrestrial and/or wading niche, as in the many giant flightless birds we are more familiar with.

Azhdarchids and Obama

Figure 13. Click to enlarge. Here’s the 6 foot 1 inch former President of the USA alongside several azhdarchids and their predecessors. Most were knee high. The earliest examples were cuff high. The tallest was twice as tall as our former President. The doubling and doubling again in size was made possible by giving up the constraints of flying. 

 

References
Habib MB 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, 159-166.
Witton MP and Habib MB 2010. On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PloS one, 5(11), e13982.

markwitton-com.blogspot.com/2018/05/
Seven problems with the quad launch hypothesis

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

The Origin of the Pterosaur Sternal Complex

It is a common and mistaken paradigm that pterosaurs appeared out of nowhere, seemingly unrelated to other prehistoric reptiles. Those who say this (and the list is long) also judiciously avoid any discussions of pterosaurs as lizards or fenestrasaurs. Their investments in the outmoded and unsupportable archosaur hypothesis have not provided answers — and never will. Here we will take a look at the development of the sternal complex of pterosaurs evolving from the most parsimonious sister taxa yet discovered (Peters 2000a, 2007).

The Pectoral Girdle in Huehuecuetzpalli
The story begins with Huehuecuetzpalli (Reynoso 1998), a basal tritosaurid lizard with a fairly typical pectoral girdle (Figure 1). A T-shaped interclavicle and sinuous tapered clavicles anteriorly framed the short scapula and fenestrated but otherwise discoidal coracoid. A broad sternum was located at the posterior tip of the interclavicle. The coracoid was free to rotate between the clavicles, interclavicle and sternum, increasing the range of motion of the humerus.

The Pectoral Girdle in Cosesaurus
Several changes to this pattern can be seen in the basal fenestrasaur and tritosaur, Cosesaurus (Figure 1). The interclavicle developed an anterior process. The sternum moved anteriorly, now dorsal to the transverse processes of the interclavicle. The clavicles were shorter, no wider than the sternum and aligned with the anterior rim of the sternum. The coracoids were relatively larger and considerably narrower as the anterior fenestrations expanded until just the quadrant-shaped posterior rim remained. The scapula was strap-shaped with a long posterior process extending over several more dorsal ribs. With the sternum leading edge now anterior to the interclavicle trailing edge, the coracoids had no room to move and their ventral stems became socketed and essentially immobile, resembling the configuration in birds and serving as a precursor to the configuration in pterosaurs.

 

Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex. Figure 1. The evolution of the pterosaur pectoral girdle and sternal complex featuring Huehuecuetzpalli, Cosesaurus, Longisquama, and the basal pterosaur, MPUM 6009.

The Pectoral Girdle in Longisquama
In Longsiquama (Figure 1) the interclavicle, clavicles and sternum are closely integrated, as in pterosaurs. Distinct from all other tetrapods, the clavicles curved posteriorly, extending to the posterior rim of the crescent-shaped sternum, which they frame. The cruciform interclavicle extended ventrally to form a small keel. Taphonomically displaced to beneath the throat, the overlapping clavicles were mistaken by Jones et al. (2000) for a bird-like furcula (fused clavicles in birds).

The Pectoral Girdle in Pterosaurs
In basal pterosaurs (Figure 1) there were few changes from the Longisquama pattern. So the sternal complex (Wild 1994), like many other aspects of pterosaur morphology, had evolved before the advent of large pterosaurian wings (Peters 2002, contra Bennett 2008).

Summary
All these changes could never have taken place if Cosesaurus was restricted to a typical quadrupedal configuration. The forelimbs had to become elevated from the substrate in a bipedal configuration, as imagined (based on morphology) in its phylogenetic predecessors, Lacertulus (Carroll and Thompson 1982) and Huehuecuetzpalli — and as evidence by matching Cosesaurus pedes to Rotodactylus tracks (Peters 2000b) which were ocassionally bipedal. Cosesaurus had a pectoral complex essentially and mechanically identical to that of pterosaurs (and broadly similar to that of birds). So it seems likely that it was also flapping, probably in some sort of territorial or mating ritual, long before gliding and flying were possible in its descendant taxa, Sharovipteryx, Longisquama and pterosaurs.

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 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Carroll and Thompson 1982. A bipedal lizardlike reptile fro the Karroo. Journal of Palaeontology 56:1-10.
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
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Peters D 2000a. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2000b. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
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.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.

Sharovipteryx and the Origin of Pterosaurs

The bizarre hind-wing glider, Sharovipteryx mirabilis, has confounded and intrigued paleontologists since 1971 when Alexander G. Sharov first described it. The most prominent aspects of the fossil are the extremely long hind limbs, trailed by extensive extradermal membranes called uropatagia. While several readily visible aspects of Sharovipteryx immediately recall pterosaurs (attenuated tail, longer tibia than femur, hollow bones, elongated ilium. sacrum of way more than two vertebrae, elongated pedal 5.1, dermal membranes, among others), the reduced forelimbs were cause for concern in a pterosaur sister taxon.

 

Sharovipteryx mirabilis

Figure 1. Sharovipteryx mirabilis in various views. Click to learn more.

Poorly preserved?
Sharovipteryx
has been described as “poorly preserved” even though the finest details are preserved in its extradermal membranes. The skull is crushed, but all the details are visible. Insects are preserved with and within Sharovipteryx. A beetle lies nearby. A winged ant or wasp is found in the skull. Shcherbakov (2008) described the Lagerstätte formation from which Sharovipteryx was found. The paleoenvironment (Madygen Formation, Osh Region in Kyrgyzstan, Early Triassic, 228 mya) may be reconstructed as an intermontane river valley in seasonally arid climate, with mineralized oxbow lakes and ephemeral ponds on the floodplain. After amber, it may be the best formation for preserving insects.

Early Errors
Peters (2000) attempted to trace the skull elements of Sharovipteryx, but I assumed the split at the back of the skull must have been a pterygoid. Instead it represents a domed cranium. In my rookie year as a paleontologist, I made several mistakes, this one among them. Later I was able to discern and correct my error. I also found more elements of the forelimb. All these can be seen here. No one else has attempted a detailed tracing and identification of the elements before or since.

Subsequent Corrections
There is word that some further preparation has occurred, according to Hone and Benton (2007), who reported, “In any case, the true arms of Sharovipteryx have now been found buried in the matrix (R. R. Reisz, pers. comm., 2003) and this confirms that Peters (2000) supposed arm was incorrectly identified.” It is not clear that Hone and Benton (2007) actually had access to the data itself, but in their zeal to discredit Peters (2000) they latched onto this hearsay. Unfortunately, the Reisz data have not been made available and have not been published in the eight years that have followed. Concurrently, as mentioned earlier, I was able to correct earlier mistakes. The forelimb elements I found matched left to right and fell in line in all morphological aspects between the two sister taxa of Sharovipteryx, Cosesaurus and Longisquama (Peters 2006). These included a tiny pteroid and preaxial carpal, bones otherwise found only in fenestrasaurs, including pterosaurs. I also identified prepubic bones and a hyper-elongated ilium in Sharovipteryx. These traits are also restricted to fenestrasaurs including pterosaurs. Prepubes acted like elongated pubes, adducting the sprawling hind limbs.

The pelvis and prepubes of Sharovipteryx.

Figure 2. The pelvis and prepubes of Sharovipteryx.

Truncated Studies
Following his  studies of the uropatagia in Sordes (Unwin DM and Bakhurina NN 1994), Dr. David Unwin (2000a, b, c) flirted briefly with Sharovipteryx as a pterosaur sister taxon, but has ignored it ever since. Unfortunately in his update he used Sharov’s own figure from 1971, rather than providing an updated figure.

In his book, The Pterosaurs From Deep Time, Unwin 2006 asked if Sharovipteryx could be ancestral to pterosaurs, then answered, “Probably not. Because it is almost the same geological age as early pterosaurs and, with its remarkably long neck, already highly specialized.” While referencing nearly every other paper and worker on pterosaurs, all papers written by yours truly (Peters 2000 and 2002 among them) were overlooked and ignored. Rather he opted to continue the old paradigm that, “pterosaurs sit in splendid isolation, definitely related to, but somehow remote from, other diapsids.” Unwin said there was no antorbital fenestra and the arms were extraordinarily short and small. While the latter is true, the former is not. Unwin never performed a cladistic analysis with Sharovipteryx and other pterosaur ancestor candidates to test the results of Peters (2000).

Following Gans et al. (1987), Dyke et al. (2006) described Sharovipteryx as a “delta-wing” flyer. Unfortunately they provided no evidence of membranes anterior to the hindlimb, but imagined them instead.

With such small forelimbs and such long hindlimbs, Sharovipteryx would have been a full-time biped, a fact that has been largely overlooked. As a biped, Sharovipteryx could have done other things with its forelimbs, such as gliding and flapping.

Sharovipteryx would have been a consummate glider. The enlarged hyoids extended the neck skin into strakes (leading edge root extensions), an aerodynamic structure found on several modern jet fighters. The ribs extended laterally, forming a small round pancake. Manual digit 4 extended further than the other digits. Since both sister taxa (Cosesaurus and Longisquama) had trailing edge membranes, it is likely that Sharovipteryx also had them. Rather than a delta wing, the membranes had a deeper chord distally, creating a canard wing configuration.

Due to the stem-like coracoid and strap-like scapula, Sharoviptyerx likely flapped its forelimbs, not only to show excitement and attract attention when grounded, but to create thrust and lift when aloft. The large, fiber embedded uropatagia that trailed the sprawling hind limbs of Sharovipteryx provided the majority of lift and extended through the center of balance. Other tiny membranes extended anterior to the lower tibia and mid femur. Longisquama was similar in configuration, but with longer forelimbs. Pterosaurs were also similar, but with even longer wing fingers.

The hind legs of Sharovipteryx provide a good model for the configuration of most pterosaurs, sprawling in flight. On land, whenever the knees were lower than the hip socket, which was probably typical, the right angled knees returned the ankles to beneath the torso, as in pterosaurs.

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 G, 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 13(4):415–426.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Peters, D. 2000b. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7(1):11-41.
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 2002. A New Model for the Evolution of the Pterosaur Wing—with a twist. Historical Biology 15:277-301.
Peters D 2006. The Front Half of Sharovipteryx. Prehistoric Times 76: 10-11.
Shcherbakov DE 2008. Madygen, Triassic Lagerstätte number one, before and after Sharov. Alavesia 2:113-124. online pdf
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
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 2000a. Sharovipteryx: what can it tell us about the origin of pterosaurs?
48th Symposium of Vertebrate Palaeontology and Comparative Anatomy, Portsmouth,
England, Monday 28 Aug. – Sunday 3 September.
(http://www.soft.net.uk/richardforrest/svpca2000/svpca2000.page.intro.html)
Unwin DM 2000b. Sharovipteryx and its significance for the origin of the pterosaur
flight apparatus. 5th European Workshop on Vertebrate Palaeontology, 27.6.2000
– 1.7.2000, Staatliches Museum für Naturkunde Karlsruhe (SMNK) Erbprinzenstr.
13 D-76133 Karlsruhe Germany (http://www.alettra.de/ewvp5/index.htm)
Unwin DM 2006. The Pterosaurs from Deep Time. Pi Press, New York, NY.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle Triassic of Kirgizia, pp. 177–186. In: Benton M. J., Unwin D. M. & Kurochin E. “The age of Dinosaurs in Russia and Magnolia”, Cambridge University Press, Cambridge.

Seven problems with the pterosaur wing launch hypothesis

How did pterosaurs take off?
Unlike bats and birds, pterosaurs, the first flying vertebrates, are all extinct. We can only imagine what it was like to see them fly, land and take off. It used to be thought that pterosaurs hung by their toes from cliff faces, like bats, before becoming airborne. Illustrations have shown pterosaurs clinging inverted to tree branches ready to drop off. The idea of bipedal pterosaur running downhill into a headwind was floated by Chatterjee and Templin (2004), but had few takers. Bennett (1997) imagined the first pterosaurs leaped with their hind limbs into flight. Padian (1981) imagined they ran first.

Vaulting pterosaur

Figure 1. Click to see video of the Habib/Molnar quadrupedal pterosaur launch sequence.

Recent studies by PhD candidate, Mike Habib (2008 pdf), on the dynamics of the pterosaur launch proposed a novel launch method (Figures 1 and 2.) based on the technique of Desmodus rotundus, the vampire bat (Schutt et al. 1999). The vampire launches itself quadrupedally, principally with its muscular forelimbs, opening its wings at the peak of its launch. Habib documented the great disparity in the comparative sizes and strengths of pterosaur forelimbs vs. the hindlimb and how these compared to bird limbs. Vampire bats are similar. In birds, Habib reported, the hind limbs provide the primary source of propulsion for launch, either by running or leaping, immediately before the wings take over. Habib reported that pterosaurs have stronger forelimbs than hindlimbs, just the opposite of birds. Thus, Habib reasoned, since all pterosaurs were quadrupeds (this is questionable, see below), they must have employed their strongest limbs, their wings  (this is also questionable, see below), to take off. Habib reported, “…expected flapping forces alone seem insufficient, at present, to explain the structural strength ratios of pterosaurs; it is simply implausible that pterosaurian lift coefficients would be several times higher than in birds…”

Dr. David Hone agreed with this hypothesis, “If pterosaurs actually launched like birds, with the hindlimbs producing most of the force, then the ratio of their bone strength values should be about the same as birds, and big pterosaurs should have slender wing bone elements (especially the proximal elements, like the humerus) and big, robust hindlimb bones.  Well, it turns out that the opposite is actually the case: pterosaurs have whopping huge forelimb bones and very slender hindlimb bones, and this gets more exaggerated in big pterosaurs.” Dr. Mark Witton is in agreement here. Julia Molnar created a video to demonstrate the Habib hypothesis here. Other images can be seen here and here. The forelimb launch seems to have become the widely accepted view.

Of course, evidence for either the Habib (2008) hypothesis or the heretical bird-style take-off would have to come in the form of take-off tracks. Unfortunately we don’t know of any such tracks. We only know of one landing trace (Mazin et al. 2009, Figure 3), which came in feet first. So let’s examine each of the precepts of Habib’s hypothesis and see if any problems arise.

Animation of a landing pterosaur matched to tracks.

Figure 3. Click to animate. Animation of a landing pterosaur matched to tracks based on Mazin et al. (2009).

Problem 1. Did all pterosaurs have stronger forelimbs than hindlimbs? While most pterosaurs had a larger diameter humerus than femur, not all did. Basal pterosaurs up to, but not including, Carniadactylus and Eudimorphodon had a humerus no thicker than the femur. The same held true for a few Rhamphorhynchus specimens, Sordes, some Pterodactylus specimens and at least one germanodactylid. The flightless pterosaur had a tiny humerus. Some pterosaurs, such as Zhejiangopterus and Fenghuangopterus had a much shorter humerus than femur. Thus the femur in these taxa would have had much more leverage, travel and associated muscles to launch the pterosaur further and higher. Why did some pterosaurs have a large diameter or longer humerus? I don’t know. I can’t see a clear phylogenetic pattern yet.

Kangaroo skeleton compared to a leaping pterosaur skeleton

Figure 4. Click to enlarge. Here a kangaroo skeleton is compared to that of a quadrupedally leaping pterosaur. The red arrows on the kangaroo indicate the major muscle pulls employed during each leap. Even with all those muscles, tensioned tendons and bone levers, kangaroo leaps only lift the toes to the height of the ankles. The pterosaur is less well-equipped with only a single major lever, the elbow as it straightens a very short distance, bound by the propatagium in front _preventing_ overextension of the elbow.

Problem 2. Were the proximal forelimb elements long enough and strong enough to produce the required height and airspeed during a forelimb launch to deploy the very long folded wings and initiate the first flap?
Habib (2008) reports the forelimb bones were more than strong enough. Were they long enough? The answer seems doubtful if one compares the skeleton of our greatest living leaper, the kangaroo with that of a pterosaur (Figure 4). Despite having five muscle groups from pelvis to toe contracting in a coordinated series, kangaroo initial leaps raise the toes only to the heights of the ankles. By contrast, pterosaurs had only their elbows and wrists to extend and they could extend their elbows a relatively shorter distance, not counting the effect of the propatagium, which in birds and bats prevents exactly this sort of overextension of the elbow. Even the vampire bat leaves 15-20 degrees of flex at the elbow during takeoff.

Problem 3. The evolutionary pathway to forelimb launching.
Pterosaur predecessors were bipeds that ran and/or launched themselves with their hind limbs. Basalmost pterosaurs were also bipeds, unable to touch the substrate with their hands. Nevertheless, the vast majority of pterosaurs had forelimbs long enough to touch the substrate without bending over. Thus quadrupedal locomotion was secondarily derived. That’s why pterosaur finger tracks point laterally and posteriorly instead of anteriorly, as in other tetrapods. At this point the forelimb launch pattern could have evolved. Meanwhile, the forelimbs/wings of pterosaurs were used for flapping, flying, clinging to tree trunks and, in beachcombing genera forelimbs supported the anterior torso while walking quadrupedally. However, in beachcombers, the forelimbs produced no forward propulsion vectors. The planted hands were never behind the elbows and shoulders. Pterosaur forelimbs acted more like crutches than traditional walking forelimbs (see walking pterosaur movie here).

So were does the impetus for a forelimb launch come from? There doesn’t appear to be an evolutionary sequence demonstrating the gradual acquisition of a rapid extension of the forearm at the magnitude needed to launch a pterosaur high enough to extend the wings and initiate flapping. Nor does there appear to be any change in pterosaur shoulder and elbow morphology that would signal such a change in behaviour. Moreover, flexion of the elbow would be constrained by the long pteroid in a few taxa and extension would be constrained by the propatagium in all taxa. The question of why most pterosaurs have a thicker, stronger humerus than femur remains unanswered. No skeletal correlates have been documented yet to gauge a large humerus or a large antebrachium with large claws, a large head or any other skeletal character. Such characters change one way or the other within genera such as Pteranodon and Rhamphorhynchus.

Problem 4. The margin of error.
Avoiding the narrow margin of error and calamity a pterosaur experiences every time it would have to snap open its (sometimes huge) wings during a forelimb launch (thousands of times during a lifetime) without ever striking the ground seems to tempt the odds. Moreover, the power and coordination needed to complete the vault and extend the wings in this fly-or-crash scenario gives little room for a learning curve in younger weaker pterosaurs or in the evolution of such a maneuver from predecessors that were already adept at performing the standard hind limb leap.

Here are three animations of Pteranodon (Figures 5-7) in the process of taking off. Two portray the widely accepted wing launch model (one successful and one not successful) and one portrays the heretical bird-style launch from a standing pose. Click each one to see the animation.

Successful Pteranodon wing launch based on work by Habib (2008).

Figure 5. Click to animate. Successful Pteranodon wing launch based on work by Habib (2008). Here the initial propulsion is strong enough to provide sufficient thrust and height for Pteranodon to unfold its wings and get off one downstroke. The timing of this launch has been slowed down from its hypothetical speed to help show what happens.

Unsuccessful Pteranodon wing launch based on Habib (2008).

Figure 6. Click to animate. Unsuccessful Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Successful heretical bird-style Pteranodon wing launch

Figure 7. Click to animate. Successful heretical bird-style Pteranodon wing launch from a standing start into a headwind  in which the hind limbs produce the initial thrust and the first downstroke takes over immediately in the manner of birds. Without a headwind a running start, like an albatross, would probably be required (see below). Note three wing beats take place in the same space that only one wing beat takes place in the Habib/Molnar model.

Problem 5. Opening time for the big wing finger.The vampire bat is able to snap open its wings in an instant at the acme of its leap because the finger bones are mere splints with little mass and therefore little momentum and drag. Moreover they can curl like human fingers and extend at least as quickly. Not so pterosaur wing fingers. They are long, stiff and massive by comparison. In many pterosaurs, the wing phalanges are the largest bones in the specimen, and some can exceed the skull in length. That means, relative to the vampire bat, the largest pterosaur wings would have to take longer to accelerate to opening speed, and then promptly decelerate to a stop at the acme of the leap. The individual phalanges didn’t bend much at all, so the entire wing finger acted like a very long rod or pipe. Imagine swinging a 1-2 meter length of PVC pipe through 180 degrees and stopping it precisely. That’s what a big pterosaur wing would have to do if it snapped open in the moments after lift off in the Habib/Molnar model. By contrast, in the bird-style model, a less snappy pterosaur can take as much time as a bird does to open its wings.

Nyctosaurus in lateral view

Figure 8. With such a short humerus it appears unlikely that this Nyctosaurus could achieve a forelimb launch of sufficient height and length to deploy those long wing fingers before crashing.

Problem 6. Incorrect reconstruction.
The Habib/Molnar reconstruction of the Anhanguera manus (Figure 9) had a few inaccuracies. The three free fingers were way to short. All pterosaurs have subequal metacarpals 3 and 4. Thus finger three (and usuallly two and one) always extended beyond the big wing metacarpolphalangeal joint. Ichnites confirm this. Only digits 1-3 ever appear in fossil handprints. The folded knuckle of finger 4 never made an impression. If knuckle 4 never touched the substrate then it could not be used to pinch the extensor tendon during the vault/preload phase of the quadrupedal launch, which was supposed to store energy prior to a sudden release of impulse power. Also, the metacarpals of all pterosaurs actually lined up anteriorly, as in all tetrapods, including lizards and fenestrasaurs. The Habib/Molnar reconstruction incorrectly placed metacarpals 1-3 on the dorsal (in flight) surface of metacarpal 4.

Errors in the Habib/Molnar reconstruction of the pterosaur manus

Figure 9a. Click to enlarge. Errors in the Habib/Molnar reconstruction of the pterosaur manus. The fingers were too small and incorrectly placed. The extensor tendon should not run over the extensor tendon process. It should split and run on either side of the knuckle.

The so-called catapult mechanism in pterosaurs

Figure 9b. Left: The so-called catapult mechanism in pterosaurs. Right. The actual design of pterosaur (in this case Anhanguera/Santandactylus) fingers.

The Habib/Molnar model illustrated the extensor tendon running over the extensor tendon process (which would have enabled it to be pinched during launch. However, if pterosaurs followed lizards and other tetrapods (as they probably did), the extensor tendon would have split at the knuckle, inserting on both sides of the first phalanx a short distance away from the knuckle. Such a split would have prevented the sort of tendon pinching called for in the Habib/Molnar model. Flexors were similar and a more distal insertion point permitted complete wing folding (shown in gray below, and more on that subject later) than would have been impossible with the Habib/Molnar model with insertion at the flexor process tip. That sort of engineering would only have permitted folding the wing at right angles before running out of pull.

Problem 7. Did pterosaurs really have weak hind limbs?
On pterosaur.net Habib reported, “For all of the large pterosaurs, insufficient strength was present in the hindlimbs to initiative a bird-like launch. In addition, for most species, a bipedal launch position would have placed the wings at an inappropriately high angle of attack.” Of course, modern stilts, flamingoes and storks do very well in their bird-style launches, even with their “stilt”-like leg bones. Bending forward at the hip would have positioned the wings at the appropriate angle of attack (see below).

Bipedal lizard video marker

Figure x. Click to play video. Just how fast can quadrupedal/bipedal lizards run? This video documents 11 meters/second in a Callisaurus at the Bruce Jayne lab.

As descendants of bipedal lizards with sprawling femora (see below), pterosaurs would have run like highly improved lizards (see video), likely during take-off without a headwind. The Bruce Jayne lab in Cincinnati, Ohio, documented a zebra-tailed lizard, Callisaurus draconoides, running quadrupedally and later in the video, bipedally (Irschick and Jayne 1999). Note, the heels of the lizard never touch the ground. Speeds reach 5 m/sec or 11 mph for a 10 cm (snout/vent) length. Note that footfalls occur every three body lengths. That’s fast! What could a better-equipped pterosaur do? We’ll have to wait for running/takeoff footprints to find out, but here is an animation of a running Quetzalcoatlus to fire-up your imagination (Figure 10). Successive footfalls occur at a snout to vent length, which is quite a distance!

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 10. Quetzalcoatlus running like a lizard prior to takeoff. Click to animate.

Albatross video showing take-off

Figure 11. Click for video. Albatross take-off in a no headwind situation. Running and flapping provides sufficient airspeed to provide lift.

It is important to note that bird legs and pterosaur legs had one fundamental difference: bird femora are not only tucked close to the body they are constrained by torso skin from moving much. So bird strides really begin at the knee. Birds elongate their metatarsals to produce yet another flexible leg section (the so-called “backwards knee”). By contrast, pterosaur femora swing from the hip and they all had relatively short metatarsals. Thus any mathematical comparisons, like those performed by Habib (2008) between the two types of flyers are going to be affected by this basic difference.

We end with a video (Figure 11) of several albatross taking off in a no headwind situation. With headwind an albatross need only unfold and lift its wings to become airborne.

I respect Mike Habib’s mathematical studies on pterosaurs, but I remain his loyal opposition for the reasons listed above. We have corresponded on this problem without swaying each other. Look for more studies from him in the near future. We’re both looking for those elusive pterosaur take-off tracks that will prove our hypotheses!

ADDENDUM: 
Every week since it was originally posted, this report on pterosaur wing launching has been a very popular post. There’s more to this story in a more recent blog here.

References:
Bennett SC 1997.
The arboreal leaping theory of the origin of pterosaur flight. Historical Biology 123(4): 265-290.
Chatterjee S and Templin RJ 2004.
Posture, locomotion, and paleoecologyof pterosaurs. The Geological Society of America Special Paper, 376:1–63.
Habib MB 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana B28:159-166.
Mazin J-M, Billon-Bruyat J-P and Padian K 2009. First record of a pterosaur landing trackway. Proceedings of the Royal Society B doi: 10.1098/rspb.2009.1161 online paper
Padian K 1984. The origin of pterosaurs. In: Reif W-E. & F.Westphal, Eds. Proceedings of the Third Symposium on Mesozoic Terrestrial Ecosystems, Short Papers.  Tübingen, Attempto Verlag: 163-168.
Schutt WA Jr, Altenbach JS, Chang YH, Cullinane DM, Hermanson JW, Muradali F and Bertram JEA 1997.
The dynamics of flight-initiating jumps in the common vampire bat Desmodus rotundus. The Journal of Experimental Biology 200: 3003-3012.