Bird and pterosaur comparisons: Witton and Habib 2010

Keys to today’s discussion
are the variety of birds and the variety of pterosaurs. Some are analogous to one another (like storks and azhdarchids), Others, not so much (like albatrosses and azhadarchids). Our job is not to mix them up or to generalize.

Witton and Habib 2010 wrote:
“Avian biomechanical parameters have often been applied to pterosaurs in such research but, due to considerable differences in avian and pterosaur anatomy, have lead to systematic errors interpreting pterosaur flight mechanics. Such assumptions have lead to assertions that giant pterosaurs were extremely lightweight to facilitate flight or, if more realistic masses are assumed, were flightless.”

Weight vs. Lift and Thrust vs. Drag
Weight does not matter IF enough lift can be generated to overcome it. Just as drag does not matter IF enough thrust can be generated to overcome it. In the case of giant pterosaurs, AS IN giant birds, the presence of vestigial distal phalanges and/or wings is the first signal that such a pterosaur or bird was flightless. When Witton and Habib published in 2010, evidently they were unaware of the presence of ANY flightless pterosaurs even though two were known (but not published) at that time.

Witton and Habib 2010 wrote:
“Scaling of fragmentary giant pterosaur remains have been misled by distorted fossils or used inappropriate scaling techniques, indicating that 10–11 m wingspans and masses of 200–250 kg are the most reliable upper estimates of known pterosaur size.”

The chart below
(Fig. 1) agrees with the Witton and Habib wingspan estimate of 11m for Quetzalcoatlus northropi (Figs. 1–5). The weight estimate is half: 125kg, about the weight of a large ostrich, which has nearly solid leg bones, but a much smaller head and neck. The giant head and neck in azhdarchids shift the center of lift and balance forward of the wing root, where all other volant pterosaurs, birds and airplanes balance.

Figure 1. Estimating giant azhdarchid weight from estimated height and comparables with similar smaller taxa.

Figure 1. Estimating giant azhdarchid weight from estimated height and comparables with similar smaller taxa.

Desperate to put pterosaurs into their own category,
Witton and Habib wrote,“Not only may doubt exist over the relationships of the extinct group to modern animals, but their anatomy may be so different to that of extant forms that few meaningful insights can be drawn about their palaeobiology even if their taxonomic context is well understood. Both problems face researchers of pterosaurs, animals of controversial phylogenetic affinities [1][3] and very distinctive anatomy.” 

The authors chose to ignore the cladograms 
of Peters 2000a, b; 2007) which nested pterosaurs with lepidosaurs, tritosaurs and fenestrasaurs. Witton and Habib citations included Bennett 1996 who nested pterosaurs with Scleromochlus or Erythrosuchus; Benton 1999 who also nested Scleromochlus as a sister; and Hone and Benton 2008, which reached no conclusions after deciding to exclude taxa from Peters 2000 when those taxa were found to attract pterosaurs). Peters 2000b added taxa to Bennett 1996 and Benton 1999 to invalidate their findings.

Try not to 
exclude taxa and authors in order to preserve the invalid status quo, traditions and paradigms.

Without citations, Witton and Habib wrote,
“Modern birds are commonly suggested to provide the best ecological and anatomical analogue and, by far, the most comparisons are made between pterosaurs and marine birds such as members of Laridae and Procellariiformes.” Laridae include gulls, terns and skimmers. Procellariiformes include albatrosses, petrels and shearwaters.

For reasons unknown, except to bolster there a priori hypothesis
Witton and Habib omit similarities to large storks, like the saddle-billed stork (Fig. 1; genus: Ephippiorhynchus, weight = 7.5kg, 16.6lbs), which greatly resembles in many regards the human-sized smaller Quetzalcoatlus (Figs. 1, 2). Witton and Habib deride published pterosaur weight estimates for similar sizes as “extremely lightweight.” Indeed it is difficult to believe that a stork as tall as human should only weigh twice as much as human newborn, but facts are facts.

Quetzalcoatlus neck poses. Dipping, watching and displaying.

Figure 2. Quetzalcoatlus neck poses. Dipping, watching and displaying.

Getting down to the crux of their hypothesis,
Witton and Habib write: “Observations on avian flight have also heavily influenced research into pterosaur flight mechanics. It has commonly been assumed that pterosaurs and birds would take off in a similar way (e.g. [6][17][20]) suggesting that pterosaurs leapt into the air with flapping wings or ran for a short duration to achieve the speeds necessary for flight.” This all sounds reasonable, but then Witton and Habib counterstrike with, “Studies into pterosaur flight [citations follow in the next paragraph] suggest that the largest pterosaurs would struggle to take off with such a strategy, however, and many have concluded that giant pterosaurs required specific environmental conditions to launch and must be atypically lightweight to reduce the power required for flight. Why mix up weight with power? (See above.) Lift counteracts weight and thrust (power) counteracts drag. That’s what every pilot learns.

Then Witton and Habib cite several pterosaur aerodynamics papers
of dubious or irrelevant content because no stork-like birds are mentioned, different atmospheric and/or gravitational factors were imagined to be at play, dimensions were over-estimated, etc.

Witton and Habib employ an out-dated phylogeny
when they call Pteranodon an “ornithocheiroid.” Pteranodon is a pteranodontid, derived from a clade of germanodactylids in the large pterosaur tree (LPT, 239 taxa). Ornithocheiroids find their ancestry in tiny scaphognathids.

Witton and Habib wrote:
“pterosaur scaling coefficients (e.g. [19][24]) predict that a 13 m span pterosaur will mass almost twice that of a 10 m span individual, stressing the importance of accurately assessing the wingspans of these forms.” Not if the difference between the two wingspans involve only the difference between traditionally proportioned distal wing phalanges and vestigial ones. As you can see, Witton and Habib were not thinking of those vestigial distal wing phalanges on giant azhadarchids as no longer useful vestiges.

Figure 1. Quetzalcoatlus in dorsal view compared to two much smaller azhdarchids from the Solnhofen formation, JME-Sos 2428, a flightless pterosaur, and BDPG 1911 I 31, a volant pterosaur. The wingspan of Quetzalcoatlus does not match that of the much smaller azhdarchid, so perhaps the giant was unable to fly. At least, this is the evidence for flightlessness.

Figure 3. Quetzalcoatlus in dorsal view compared to two much smaller azhdarchids from the Solnhofen formation, JME-Sos 2428, a flightless pterosaur, and BDPG 1911 I 31, a volant pterosaur. The wingspan of Quetzalcoatlus does not match that of the much smaller azhdarchid, so perhaps the giant was unable to fly. At least, this is the evidence for flightlessness.

False data on pterosaur growth:
Witton and Habib wrote: “Both estimates, however, isometrically scaled the bones of smaller azhdarchids until they attained cervical vertebra metrics comparable with those of Arambourgiania, a method that ignores Wellnhofer’s observations that pterosaur necks grow with positive allometry against body size.”

Wellnhofer’s observations were wrong.
They were reported at a time when tiny Solnhofen pterosaurs were considered juveniles of larger forms. The LPT shows those hummingbird-sized taxa were tiny adults experiencing phylogenetic miniaturization as transitional taxa. Now we have juvenile / adult pairings for many pterosaurs and neck length does not grow with positive allometry. Why? Because pterosaurs are lepidosaurs, not archosaurs, a fact lost on Witton and Habib because they chose to ignore the published literature on that subject.  And they chose to blindly accept reports without testing because they fit their pre-conceived ideas.

More false data on neck length:
Witton and Habib cited Tschanz 1988 when they wrote: “Such allometry in neck length is known in a suite of other long-necked animals including giraffes, sauropod dinosaurs; protosaurs [sic = protorosaurs] and plesiosaurs. Tschanz falsely assumed he was dealing with an ontogenetic series rather than the actual phylogenetic series. After testing, phylogenetically larger protorosaurs in the two genera Tanystropheus and Macrocnemus, had longer necks. Both are members of a lepidosaur clade (Tritosauria) in which in all testable cases juveniles grow isometrically, not allometrically. Giraffes, sauropods and plesiosaurs are irrelevant because they are not related to pterosaurs.

Citing others to prove your own point can get you published,
as Witton and Habib demonstrate, but it is not good science. Excluding relevant citations to prove your own point is also not good science. Remember when Dr. Witton labeled me a ‘crank’? Take the emotion out and test prior hypotheses and test them good with a wide gamut phylogenetic analysis that minimizes taxon exclusion, like the large reptile tree (LPT, 1565 taxa) and the LPT. Otherwise it’s like repeating a rumor or a lie.

Witton and Habib conclude:
“It is likely, therefore, that azhdarchid necks demonstrated similar allometry. If so, the 5 m span forms used in predicting an 11–13 m wingspan for Arambourgiania would have relatively short necks and, when scaled isometrically to fit the neck of Arambourgianaia, will over-estimate its wingspan.” I presume you know what happens to people who assume, especially in science. Test, even though it means more work.

Witton and Habib focus on weight estimates,
bone strength and flap gliding performance, all hypothetical. Not one sentence discusses the actual presence of vestigial (=tiny, useless) phalanges of the wing or comparisons of wingspan to much smaller phylogenetically related pterosaurs with longer relative wingspans (Fig. 3) due to unreduced distal wing phalanges. Without the proper phylogenetic context, my friends, we are all lost and guessing.

No comparisons were made
to the largest living bird, the ostrich (Struthio), or transitions to flightlessness in other bird lineages. How do you know what to look for, unless you can make comparisons to something you’ve seen before.

Witton and Habib fell for the myth
of the bat wing model pterosaurs (contra Peters 2002). And they continue to promote a tiny vampire-bat quad launch from the ground despite the many hazards and inefficiencies of doing so. Dispensing with hard data found in fossils (Fig. 4; Peters 2002), Witton and Habib chose the bat wing model promoted by Witton 2008. Ironically Witton and Habib suggest more efficient flight for the shorter, deeper wingspan when airplane gliders use the long span, narrow chord shape.

Witton and Habib report,
“…authors have commented that pterosaur femora only appear slender in comparison to their large forelimbs and [pterosaur femora} were well suited for powerful leaping (Padian 1983, Bennett 1997).”

Generalizing way too much, Witton and Habib report, 
“Bird femora are therefore simply bigger than predicted for their body mass (see discussion below), whereas those of pterosaurs are in keeping with their body size.”
Best to consider specific genera, rather than lump together moas and hummingbirds. Right? Yes and no. Consider Pelagornis (Fig. 4), the largest flying bird and Struthio, the largest living bird. Both have a long slender humerus, distinct from the more robust humerus in all pterosaurs.

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

Figure 4. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

With their blinders on 
Witton and Habib reported, “Pteranodon [is] the only giant pterosaur for which the entire skeleton is known.” Figure 4 shows this is not true. Pteranodon is not a giant pterosaur and other pterosaurs are the size of Pteranodon.  Only a few Pteranodon specimens are nearly complete. None are known from complete skeletons.

Prediction failure
Witton and Habib report, “The structure and scaling properties of giant pterosaur bones are confusing if giant pterosaurs were flightless. If giant pterosaurs had abandoned flight it may be predicted that their bone strengths would correlate well with those of comparably-sized terrestrial animals, but they appear considerably over engineered by comparison. we find it difficult to explain why pterosaur limbs were of such considerable strength if they were not subjecting their skeletons to high mechanical stresses such as those experienced during flight.”

Just because some pterosaurs were flightless
does not mean they were not using their wings for something other than flight (Fig. 5). Azhdarchid wings were still used as ski-pole-like forelimbs while walking. And with the weight of the giant skull and hyper elongate neck extending further anterior to the forelimbs, the center of balance shifted anteriorly (Fig. 2). Ironically and inexplicably, this hypothesis was not suggested by Witton and Habib. Moreover, flightless wings can still be used for thrust while running (Fig. 5), for creating chaos when under attack and their original use: as secondary sexual devices to attract the opposite sex.

Quetzalcoatlus running like a lizard prior to takeoff.

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

The Julia Molnar illustration presented by Witton and Habib
(Fig. 6) became infamous for cheating on the anatomy. Note the tiny free fingers used to promote the implantation of the massive wing finger on the substrate, which never happened in pterosaur ichnites. The fingers of this taxon actually extended far beyond the metacarpus and the pteroid nested in the bowl of the radiale.

Errors in the Habib/Molnar reconstruction of the pterosaur manus

Figure 6. Errors in the Habib/Molnar reconstruction of the pterosaur manus. Note the tiny free fingers used to promote the implantation of the massive wing finger on the substrate, which never happened in pterosaur ichnites.  Pteroid is not on the radiale and other issues. So this illustration is a big fat cheat created with more imagination than hard data, probably due to naiveté and/or improper homologs.

Apologizing for short azhdarchid wings,
Witton and Habib report, “Granted, azhdarchids do have unusual proportions that may produce the appearance of shortened wings (particularly their elongate heads and necks; shortened wing fingers and hypertrophied wing metacarpal), but their wingspans are not especially shorter than would be expected for any other lophocratian (see definition below) pterosaur of their size.” See above (Fig. 3) for a complete refutation of this statement. Fact: giant azhdarchid wingspans are considerably shorter, all other aspects of their anatomy being relatively equal.

Older, bigger = flightless?
Witton and Habib report, “It is possible, however, that giant pterosaurs represent old, flightless individuals of a species that were capable of flight when younger, their flight anatomy simply being retained from a previous stage in their life history. It seems unlikely that enormous azhdarchids would continue to develop their physiologically expensive flight apparatus, and coincidentally with a mechanically appropriate scaling regime, throughout such extensive growth under flightless conditions.”

No.
Remember this fact overlooked by Witton and Habib: it is the flightlessness of the smaller taxa (due to vestigial distal wing phalanges) that enabled the evolution of giant flightless taxa, as in flightless birds.

The largest flying pterosaurs
retained elongate distal wing phalanges and all of them reached the size of the largest flying bird, Pelagornis (Fig. 4). This, therefore, appears to be an upward limit for volant vertebrate size.

Witton and Habib report,
“If anything, the scaling regimes of pterosaur wings dictate that the flight characteristics of giant pterosaurs (the size of their deltopectoral crests, robustness of their joints) – become more exaggerated with size and age (e.g. Codorniu and Chiappe 2004), precisely the opposite of what would be expected in animals that lost their flight ability as they grew older.”

This is taking hard data and merging it with wishful thinking.
The largest azhdarchids and pteranodontids have larger deltopectoral crests and joints because they are dealing with a magnitude more weight and stress, whether walking (Fig. 1) or flying or sprinting while flapping (Fig. 5).

Fighting back, Witton and Habib report,
“On a similar note, the suggested size-gap between giant pterosaurs and their smaller relatives, said to parallel that seen between flying birds and the flightless ratites does not exist.” Yes, it does (Fig. 4). Then Witton and Habib describe reports of azhdarchids bridging the size gap of Q. northropi and the smaller, more complete Q. sp, assuming that Q. sp. could fly. It could not fly because it, too, has vestigial distal wing phalanges. It’s wings had already been clipped. This morphological fact was overlooked time and again throughout this report.

To Witton and Habib, it’s all about size and weight.
They conclude, “even the largest pterosaurs possess the same hallmarks of flight as smaller pterosaurs (as noted for Hatzegopteryx by Buffetaut et al. 2002) and, on grounds of comparative anatomy, they should be considered flighted.” 

Unfortunately,
Witton and Habib did not know, or chose to ignore, the hallmarks of flightlessness in pterosaurs because they, at the time, knew of no flightless pterosaurs. Now that we know better (and actually we knew better back then because the first flightless pterosaur JME-Sos 2428, had been known since 1970 and a manuscript was circulated to referees before 2010 and described online in 2011 here.

Witton and Habib yield to morphology when they report, 
“Therefore, while the largest pterosaurs appear to exceed the size limits for continuous flapping flight by a volant animal, there is no reason to suspect that they could not fly long distances Rather, it is reasonable to expect that so long as giant pterosaurs launched within 1 to 2 kilometres of an external source of lift, they could then stay aloft by transitioning to a soaring-dominated mode of travel after an initial burst of anaerobic power.” The authors are still avoiding the clipped wings of human-sized to giant azhdarchids.

Terrestrial locomotion.
Witton and Habib think pterosaurs could only walk or fly. They never considered the possibility of wing-assisted running (Fig. 5). Unfortunately they introduce the tangential situation in ornithocheirids when they report, “it seems unlikely that any ornithocheiroid could sustain a bipedal stance for a great length of time and would have had to overcome the hindlimb-forelimb length dichotomy inherent in their quadrupedal gait for sustained terrestrial locomotion.” See figure 4. Note the feet below the shoulder joint, the center of balance. We have a single ornithocheirid pedal ichnite (Peters 2011). See below for a bipedal ornithocheirid take-off (Fig. 10).

Back to azhdarchids
Witton and Habib report, “Taken together, these features indicate that azhdarchids were well adapted for a terrestrial locomotion and it seems likely that they spent much of their time grounded, particularly when foraging. Most azhdarchids are found in terrestrially-derived sedimentary settings, a finding that may be predicted if giant azhdarchids were flightless.” Yes! Correct (Fig. 2). The authors continue, “there is no reason why azhdarchids, like many modern fliers, cannot simply preferentially inhabit terrestrial environments.” Still not looking at those clipped wings.

Witton and Habib summarize:
“There is virtually no indication from the anatomy, biomechanics, aerodynamic performance or depositional contexts of any giant pterosaurs that they had lost their ability to fly. This is particularly so for Pteranodon, an animal with anatomy so skewed towards a glide-efficient wing morphology that its terrestrial capabilities may have been lessened. The case is not so clear-cut for azhdarchids: as pterosaurs living within continental settings and apparently possessing good terrestrial abilities, they meet some criteria that may be expected of a flightless pterosaur. However, like Pteranodon, giant azhdarchids also possess skeletons that function well as flying apparatus and were almost certainly flighted as well.” That is because they were recently evolved from smaller flighted ancestors. Still not looking at those clipped wings!

Witton and Habib deny flightlessness in any known pterosaur.
“We stress, however, that there is currently no evidence that any pterosaurs fully surrendered their flight abilities and, conversely, a wealth of evidence suggesting that all pterosaurs were flighted.” When I read this line, I thought to myself, that’s because you referees rejected the first manuscript to describe a flightless pterosaur a few years earlier. This is how pterosaur workers keep out new hypotheses and maintain the status quo found in college textbooks written by themselves and their colleagues.

Witton and Habib like the quad launch hypothesis.
The authors report, “There is good evidence that pterosaurs launched from a standing, quadrupedal start in a superficially vampire bat-like fashion, vaulting over their forelimbs and using powerful flapping to gain altitude.” Actually there is no evidence whatsoever, whether in the skeleton or the ichnites. The kinematics guarantee a face plant crash before the first wing flap can possibly take place. We looked at seven problems with the wing launch hypothesis earlier here.

Figure 3. Rough reconstruction using color tracings. Note the elongate jaws and small eye, documenting isometric growth in this pterosaur, as in all others where this can be seen.

Figure 7. Rough reconstruction using color tracings. Note the elongate jaws and small eye, documenting isometric growth in this pterosaur, as in all others where this can be seen.

Citing Pterodaustro (Figs. 7, 8) growth studies,
Witton and Habib report, “The scaling allometry of the wing metacarpal is further evidence of this launch strategy: larger pterosaurs have disproportionately long wing metacarpals, a trait echoed in pterosaur ontogeny (Codorniu and Chiappe 2004), as well as phylogeny.” This is false. There is as much difference in the metacarpus between an embryo Pterodaustro (Fig. 7) and an adult (Fig. 9) and another embryo (Fig. 8). How can we be sure we are not seeing variation in Pterodaustro phylogeny here, rather than ontogeny? Look at the differences in the two embryos. We need to find a mother with an infant together to see the similarities and differences. Remember no two tested Rhamphorhynchus specimens nested together, except one juvenile of a giant species earlier mistaken for a mid-sized form.

Pterodaustro embryo

Figure 8. Pterodaustro embryo. There certainly is no short snout/large eye here!

Witton and Habib go off the rails when they report, 
“The possibility of quadrupedal launch in pterosaurs is particularly relevant here as it may have facilitated pterosaurs to become much larger than any avian fliers: using the more powerful and robust forelimbs for takeoff sets higher mass limits on launch capability (self-citing Habib 2008) and will facilitate the evolution of much larger flying animals.” This works for tiny vampire bats with large thumbs pressing their forelimb bones into the substrate. Pterosaurs never impress their long bones into the substrate and their three free fingers are not built for launching pterosaur masses high into the air. The bigger the pterosaur, the worse this is! Ventrally oriented wing finger 4 cannot unfold fast enough, rise and sweep down before the inevitable crash in this scenario. So much easier to flap and leap at the same time, like birds (Fig. 10).

Figure 8. Elements of the MIC V263 specimen applied to the smaller PPVL 3860 specimen scaled to the length of the metacarpals. At this scale the large Pterodaustro had a shorter wing and shorter fingers with smaller unguals.

Figure 9. Elements of the MIC V263 specimen applied to the smaller PPVL 3860 specimen scaled to the length of the metacarpals. At this scale the large Pterodaustro had a shorter wing and shorter fingers with smaller unguals.

 

Witton and Habib report, “This launch strategy is entirely in keeping with the allometry of pterosaur limbs discussed above and explains why pterosaur femora are relatively slender at larger sizes compared to those of birds.”

Not at all.
Volant pterosaurs are like airplanes. The forelimbs are like the wings. The laterally extended hind limbs act like horizontal stabilizers. The hind limbs are also like the fan tails of certain birds, enhancing stability and used to initiate aerodynamic turns, rises and dives. The long tail of basal pterosaurs is a holdover from their lepidosaur past and the vane at the tail tip is a secondary sexual device as shown here.

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 10. 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.

Witton and Habib are morphologically specific
when it comes to bird take-off and flight. Too often they are less specific when it comes to pterosaur take-off and flight. Certainly hummingbird-sized taxa will have a faster flap rate and different take-off technique than more massive Pelagornis-sized taxa and stork-like taxa, let alone taxa magnitudes larger than storks. This sort of size factor was omitted or ignored. Perhaps too late in their report, the authors deliver their platitude, “there is no ‘generic’ pterosaur body plan or flight style in the same way that there is no ‘standard’ mammalian or avian bauplan or method of locomotion.” Like I said… where are the comparisons to storks when Witton and Habib talked about giant azhdarchids?

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 11a. 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 11b. 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.

 

Witton and Habib report,
“Unlike birds, pterosaur femora are only partially responsible for generating power for flight and can, therefore, scale with lower exponents than their humeri.” Actually, that scenario is like birds. The wings always help both taxa. Neither employs a quad launch (Fig. 11).

Terrestrial takeoff
Witton and Habib report, “the preferred terrestrial habits and flight-adapted skeletons of azhdarchids combine to suggest that even the largest azhdarchids could fly entirely under their own power regardless of local weather and landscape conditions. We concede that our azhdarchid flight model does suggest that flights of long-duration may be reliant on external sources of lift, but these occur through a variety of mechanisms in varied environments and climates: we do not therefore see this as a limiting factor on azhdarchid flight.” I agree. Habitat is not the limiting factor. Wing clipping is the limiting factor. All pterosaur taxa with clipped wings were flightless. End of story.

Birds compared to pterosaurs
Witton and Habib wrote: “Because bird flight mechanics differ vary with size and mass, phylogeny and ecology, selecting a group to model pterosaurs on is problematic and biases flight calculations.” This is poor thinking. Pick out a bird genus that overall resembles a pterosaur genus, then compare those two (Figs. 1, 14). Don’t cherry-pick dissimilar genera to suit your hypothesis. Don’t average out or generalize. Keep it specific. So test azhdarchids against storks (Figs. 1, 14). Test pteranodontids against Pelagornis and other giant shearwaters. There is no reason to produce an ecomorphospace when you’re only going to compare two very similar taxa, as reported by Sato et al. 2009.

Witton and Habib think they are adding wisdom to the discussion
when they belatedly report, “Although most pterosaurs have been proposed to be marine-bird analogues, recent work suggests that seabird-like lifestyles were only one ecology exploited by pterosaurs and that they were probably considerably more diverse than previously appreciated.” This is restating the obvious and should have been in their introduction. Conspicuously, Witton and Habib are losing their train of thought and drifting away from their headline topic: giant pterosaurs.

Then Witton and Habib ‘shoot themselves in the foot’ when they report,
“Procellariiform bodies are not particularly pterosaur-like with longer, narrower wings that act independently of the hindlimbs, shorter necks, smaller heads and an entirely different pelvic and hindlimb morphology.” Witton and Habib are flat-out wrong here. Their illustrations imagine deep chord bat wing membranes terminating at the ankles (contra Peters 2002 and all fossil taxa with soft tissue preservation (Figs. 4, 12).

Here's how the wing membrane in pterosaurs virtually disappeared when folded.

Figure 12. Here’s how the wing membrane in pterosaurs virtually disappeared when folded. Note only a fuselage fillet attaches to the mid thigh. CM 11426.

The danger that comes from getting or attempting to get a PhD
in paleontology is the potential need to skew or omit data to make your professor and colleagues happy that you maintained the textbook status quo. Independent researchers do not have this problem.

Figure 1. Freehand wing planform cartoon for Quetzalcoatlus from Witton and Habib 2010. There is no evidence in any pterosaur for this wing plan.

Figure 13. Freehand wing planform cartoon for Quetzalcoatlus from Witton and Habib 2010. There is no evidence in any pterosaur for this wing plan. This is based completely on fantasy and invalid traditions. See figure 3 for the validated wing planform.

Witton and Habib apparently give up when they report, 
“It seems unreasonable, therefore, to expect that the body forms of modern animals could be used to extrapolate pterosaur masses, and particularly so when the body forms in question is not especially pterosaur-like themselves.” See figure 1 for a human-sized stork similar to a human-sized Quetzalcoatlus. That’s a starting point omitted or ignored by Witton and Habit.

Assumption after assumption
“We also note that extrapolating the mass of any modern flying animal (maximum span of 3 m) to giant pterosaur-sizes (spans of 7 or 10 m) requires data projection well beyond its upper range. Such extrapolation is extremely unreliable and, in the case of the 93 kg Sato et al. Pteranodon estimate, may explain why these authors obtained a value that we consider to be almost certainly too high.” Likely true. The charts above (Figs. 1, 4) measuring height vs weight in big birds, big pterosaurs and one human shows the Sato estimate to be too high. 10-20kg (depending on which Pteranodon specimen). Witton and Habib should have presented such a chart. It would have helped their understanding and presentation.

Figure 3. Q. northropi and Q. sp. compared to Ciconia, the stork, and Pelagornis, the extinct gannet, to scale. That long neck and large skull of Quetzalcoatlus would appear to make it top heavy relative to the volant stork, despite the longer wingspan. Pteranodon and other flying pterosaurs do not have such a large skull at the end of such a long neck (Fig. 1). The longer wings of pelagornis show what is typical for a giant volant tetrapod, and Q. sp. comes up short in comparison.

Figure 14. Q. northropi and Q. sp. compared to Ciconia, the stork, and Pelagornis, the extinct gannet, to scale. That long neck and large skull of Quetzalcoatlus would appear to make it top heavy relative to the volant stork, despite the longer wingspan. Pteranodon and other flying pterosaurs do not have such a large skull at the end of such a long neck (Fig. 1). The longer wings of Pelagornis show what is typical for a giant volant tetrapod, and Q. sp. comes up short in comparison. On the other hand Q sp. has a wingspan greater than the scaled-up stork. Q. sp. may be the transitional taxon among azhdarchids. Smaller taxa could fly. Larger taxa could not fly.

Witton and Habib compare Pteranodon to Quetzalcoatlus.
“The different morphology of these forms dictates that their flight performance must have also differed.” I’ll say! One flew like an albatross. The other ran like a stork (Figs.  5, 15). The authors report, “Quetzalcoatlus plotted in the same ecomorphospace as condors and storks.” That is verified here with regard to storks, not condors.

Figure 15. Running stork. Note the wings out for balance and occasional thrust.

Figure 15. Running stork overlooked by Witton and Habib. Note the wings out for balance and occasional thrust.

Wing shape. Witton and Habib report from their imagination:
“The longer body and legs of Quetzalcoatlus could create a deep, low-aspect wing that would generate greater lift during takeoff (assuming ankle-attached brachiopatagia, while the smaller Pteranodon body and wings were narrower and produced less lift when launching but were more glide-efficient.” Witton and Habib’s illustration (Fig. 13) of their Quetzalcoaltus wing planform has no analog in the data on pterosaurs. No pterosaur has a wing plan that went any deeper than just behind the elbow (Peters 2002, Fig. 12, also see competing wing plans in Fig. 16).

Conventional wing shape in pterosaurs supported by Unwin, Elgin, Hone, Bennett, Wilkinson, Frey and others vs heretical wing shape supported by Peters and Conway.

Figure 16. Conventional wing shape in pterosaurs supported by Unwin, Elgin, Hone, Bennett, Wilkinson, Frey and others vs heretical wing shape supported by Peters and Conway. All the evidence from smaller pterosaurs supports the lower wing and uropatagium shape.

Witton and Habib conclude,
In all likelihood, there is no universal maximum for any major characteristic, including size, that can be applied to all flying vertebrates, or even most of them.” Based on the clipped wings of giant azhdarchids, I cannot support this conclusion. As in giant flightless birds, giant azhdarchid size was only attained after the loss of flight in human-sized azhdarchids. As in giant volant birds, like Pelagornis, the largest flying size in pterosaurs is likely represented by Pteranodon and the the largest ornithocheirid, the SMNK PAL 1136 specimen (Fig. 17).

The largest ornithocheirid

Figure 17. The unnamed largest ornithocheirid, SMNK PAL 1136

As an addendum:
The results of Sato et al. 2009 “cast doubt on the flying ability of large, extinct pterosaurs” including Pteranodon. So Sato et al. went too far.


References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoological Journal of the Linnaean Society 118: 261–308.
Bennett CS 1997. The arboreal leaping theory of the origin of pterosaur flight. Historical Biology 12: 265–290.
Benton MJ 1999. Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society, London B 354: 1423–1446.
Habib MB 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana B28: 161–168.
Hone DWE and Benton MJ 2008. Contrasting supertrees and total-evidence methods: pterosaur origins. Zitteliana B28: 35–60.
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx(Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Musuem. Postilla 189: 1–44.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Sato K, Sakamoto K, Watanuki Y, Takahashi A, Katsumata N, et al. 2009. Scaling of soaring seabirds and implications for flight abilities of giant pterosaurs. PLoS ONE 4: e5400.
Tschanz K 1988. Allometry and heterochrony in the growth of the neck of Triassic prolacertiform reptiles. Palaeontology 31: 997–1011.
Witton MP 2008. A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana B28: 143–159.
Witton MP and Naish D 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3: e2271.
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


Lophocratia: A subgroup of pterodactyloids (Unwin 2003) defined as the most recent common ancestor of Pterodaustro guinazui and Quetzalcoatlus northropi, and all its descendants. In the LPT, that MRCA is a basal member of the clade, Dorygnathus, which is not a pterodactyloid and includes all other pterodactyloid-grade pterosaurs. So the proposed clade ‘Lophocratia’ is a junior synonym and the intended definition is polyphyletic.

The phylogenetic conclusions
of Peters 2000a, b, 2002, 2007, 2011 are summarized online here.

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