Scathing Book Review – Pterosaurs (Witton 2013) – Dimorphodon problems

Updated June 10, 2015 with a revised Dimorphodon takeoff  (Fig. 3) that included a downstroke right at the start of the leap. 

Earlier we looked at the inaccurate cartoon produced of the hind-wing glider, Sharovipteryx by author and illustrator, Mark Witton.  Here we’ll continue up the phylogenetic line to consider the disfigurements Witton applied to a basal pterosaur.

As a purported pterosaur expert, Mark Witton, author of the new book “Pterosaurs,” should be able to accurately portray a pterosaur skeleton. Unfortunately his Dimorphodon drawing is filled with errors (Fig. 1). For comparison, an accurate portrayal based on a bone-by-bone tracing is shown below (Fig. 4).

Dimorphodon by Mark Witton, filled with errors.

Figure 1. Dimorphodon by Mark Witton, filled with errors. This pose does allow Witton to avoid the digitigrade and bipedal issues, which would be visibly odd if set in a standing pose. Is there any way this pterosaur could complete a pushup that would launch it into the air high enough to unfold that big wing finger before crashing to Earth. This is a risky move every time it’s attempted!

  1. Apparent mandibular fenestra – caused by a slipped surangular detailed here and confirmed by Bennett (2013).
  2. All pterosaurs have eight cervicals (prior to ninth vert with deep ribs)
  3. 1st and 2nd dorsal ribs should be hyper-robust and 2nd articulates with sternal complex
  4. Prepubis is the wrong shape and should articulate with the ventral pubis at its stem and against the edges of the last gastralia at its anterior process
  5. Caudal vertebrae should align with the sacrals with neural spines rising above the ilium
  6. The radius in all tetrapods originates on the lateral humerus, not the medial
  7. The pteroid should originates on the proximal carpal, not the preaxial carpal (Peters 2009, Kellner et al. 2012)
  8. Metacarpals 1-3 should align palmar sides down, out and away from metacarpal 4. This provides room for all four metacarpals to have extensors tendons.
  9. Following a wrong hypothesis, Witton orients his pterosaur fingers posteriorly, but all pterosaur tracks show digits 1-2 were oriented laterally and only digit 3  oriented posteriorly due to a spherical metacarpophalangeal joint, as in many lizards.
  10. Pedal digit 5 never flexes at pedal 5.1 (Fig. 1), but does flex nearly 180 degrees at pedal 5.2 in fossils (Fig. 4). Witton disfigured toe 5 this way in order to have it frame a uropatagium, as has been suggested for Sordes and MSNB 8950, but both are misinterpretations detailed here and here. The actual orientation of pedal digit 5 is detailed in Peters (2000, 2011, Fig. 4) and here and here.
  11. The tail and torso both appear to be too short. Freehanding, like Witton does, is not conducive to accuracy.

Forelimb pterosaur leaping
One of the hypothetical practices Witton endorses for pterosaurs across the board is the much promoted, but wisely criticized, forelimb launch. We’ve discussed its failing before. There is still no evidence for it in the fossil record, although Witton pins his hopes on a three-year-old rumor. Witton illustrates nearly all of his pterosaurs in the forelimb launch configuration (fig. 1). What Witton doesn’t show is what happens shortly thereafter. Here (Fig. 2) is Witton’s Dimorphodon trying to become airborne after attempting a mighty pushup with folded wings beneath its body and mighty triceps extensors working their hearts out. Forelimb leaping is also tremendously difficult for athletes as seen here. Click the image (Fig. 2) to animate it if not already animated.

Click to animate. Witton's Dimorphodon in the process of leaping. Note the wings are in the upswing at the apex of the leap. The opposite and equal reaction, along with gravity, pushes the pterosaur down. There's just not as much leverage and musculature here as in the vampire bat, which can accomplish this leap.

Figure 2. Click to animate. Witton’s Dimorphodon in the process of leaping. Note the wings are in the upswing at the apex of the leap. The opposite and equal reaction, along with gravity, brings the pterosaur down. There’s just not as much leverage and musculature here as in the vampire bat, which can accomplish this leap. Human athletes cannot get this high. At the apex of this leap the wings are just beginning to unfold. Moreover those big wing fingers have to swing through a ventral arc before swinging above the torso prior to the first wing beat. Finally, there’s not much forward thrust here.

There has always been a better way for Dimorphodon to leap (Fig. 3), like a leaping lizard and the vast majority of all tetrapods: by using the hind limbs, like birds, frogs and kangaroo rats do.

Figure 3. Click to animate. Dimorphodon hind limb leap - like a bird or a frog. There's nothing wrong with this method. It gets the wings open right away to provide thrust and lift at the apex of the hind limb portion of the leap. The thighs are massively muscled, more so than the forelimbs. The extension and flexion of the toes provide that last little umph! to the take-off, as in frogs and kangaroo rats. And let's remind ourselves, pterosaurs were fully capable of bipedalism and leaping, as shown here.

Figure 3. Click to animate. Dimorphodon hind limb leap – like a bird or a frog. There’s nothing wrong with this method. It gets the wings open right away to provide thrust and lift at the apex of the hind limb portion of the leap. The thighs are massively muscled, more so than the forelimbs. The extension and flexion of the toes provide that last little umph! to the take-off, as in frogs and kangaroo rats. And let’s remind ourselves, pterosaurs were fully capable of bipedalism and leaping, as shown here.

Exceptions include tiny vampire bats (Fig. 4) which arrived at forelimb leaping secondarily, as a bi-product of their lifestyle and the extremely weak legs of bats in general. Primates, jumping rodents and flying lemurs are much better at hind limb leaping than bats are. Click here to see the video of the top 10 fastest, highest jumping animals.

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 4. 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.

Size matters!
Dimorphodon is not a large pterosaur. Even so, it is several times larger than a vampire bat (Fig. 4). Its not just the effect of gravity, which increases with the cube of height, but it’s also the cushion of air, that becomes so much more cushiony the smaller a creature gets and as it adds surface area. That’s why vampire bats can get away with forelimb leaping while pterosaurs larger than a vampire bat likely could not. And giraffe-sized pterosaurs could probably leap with their forelimbs about as high as a giraffe can leap with its forelimbs.

At least he’s consistent
Witton incorrectly pastes dorsal metacarpals 1-3 back-to-back against metacarpal 4 (now rotated palmar side posterior to enable wing folding, Fig. 1). That orients the free fingers palmside anterior during flight and all posteriorly when hyperextended during terrestrial locomotion (Fig. 1). Unfortunately that doesn’t match pterosaur handprints, which are lateral for digits 1 and 2 (sometimes anterior for digit 1) and posterior for digit 3 due to a spherical joint there. That also means when a pterosaur wants to clamber up a tree, it can’t because in Witton’s view the palms are face up, as if begging.

The better orientation is palm side down while flying (or palms medial (like clapping) when walking). That also gives all four forelimb digits plenty of room to have extensor tendons. The preferred configuration also means the fingers hyperextend laterally when walking with the exceptional digit 3 oriented backwards to match ichnites. Details here.

But not always consistent
Witton’s figure 7.10 has the palms facing each other while the pterosaur is floating. They should be palms up in his view.

Whether pterosaurs had their fingers oriented laterally or posteriorly, that’s arrived at secondarily, because no tetrapods do this plesiomorphically. Their fingers always point in the direction of travel. The secondary lateral placement of the fingers on the substrate occurred after a bipedal phase shown in Cosesaurus/Rotodactylus and emphasized in Sharovipteryx. In Witton’s hypothetical scenario, the one that ignores real fossils, pterosaurs and their ancestors were never bipeds.

Pterodactylus walk matched to tracks according to Peters

Figure x. Click to animate. Plantigrade and quadrupedal Pterodactylus walk matched to tracks

No Bipedal Footprints?
Along with the adoption of the forelimb launch, Witton (2013) rejects the bipedal capabilities of pterosaurs, first promoted by Padian (1983) and later by Peters (2000a, b, 2011). Peters (2000a, b) recognized that pterosaur tracks known at that time were all plantigrade and quadrupedal but recognized that pterosaurs anatomy could vary and that even the quadrupdal pose included having the toes directly beneath the center of gravity, the shoulder glenoid (Fig. x). That enabled the forelimbs to be raised without changing elevating the back. Witton ignored this data. He also reports there are no records of digitigrade pterosaurs, but his book includes an illustration of one (his figure 7.9) and he ignores the several digitigrade pterosaurs in other published works (Peters 2011, Fig. 5) mentioned, referenced and illustrated here, here, herehere and here.

Digitigrade pterosaur tracks

Figure 5. A pterosaur pes belonging to a large anurognathid, “Dimorphodon weintraubi,” alongside three digitigrade anurognathid tracks and a graphic representation of the phalanges within the Sauria aberrante track. Digit 5 impressing far behind the other toes is the key to identifying tracks as fenestrasaurian or pterosaurian.

Not Digitigrade? It pays to be specific here.
Witton referenced Clark et al. (1998) who reported that basal pterosaurs, like Dimorphodon, had flat feet because they could not bend the metatarsophalangeal joint due to the squared-off (butt joint) shape. Peters (2000a) showed that Cosesaurus, an ancestor to pterosaurs, had the same sort of butt-joint metatarsophalangeal joints, and that its feet exactly matched Rotodactylus tracks, but only when the proximal phalanges were all elevated (because they could not be bent), in accord with the findings, but not the conclusions of Clark et al. (1998). Peters (2000a) also showed that many pterosaurs, from Dimorphodon Pteranodon, raised the metatarsals and proximal phalanges in the same way to produce a digitigrade pes. The reduction of pedal digit 5 in derived pterosaurs led to their becoming plantigrade. Beachcomber pterosaurs also rested on their ski-pole like arms and became quadrupeds, but those forelimbs did not provide thrust due to the placement of the hands in front of the shoulder sockets.

Cosesaurus foot in lateral view matches Rotodactylus tracks.

Figure y. Cosesaurus foot in lateral view matches Rotodactylus tracks.

Ironically,
while Witton favors the archosaur model for pterosaur origins, he rejects digitigrade pedes in pterosaurs, a trait widely found in basal dinosaurs and basal bipedal crocs.

Bipedal capability (in the manner of modern bipedal lizards), a narrow chord wing membrane and twin uropatagia solve all sorts of problems introduced and sustained by Mark Witton and the other experts he hangs with. And, there’s fossil evidence for all of this (throughout this blog and reptileevolution.com)! And none for the Witton follies.

Extension and Flexion Forelimb Limitations
Pterosaur arms cannot fully flex if they have large pteroids. The elbow joint also prevents this. Pterosaur arms cannot fully extend due to elbow limitations and the presence of the propatagium, which, as in birds, prevents overextension. These problems limit the ability of the forelimbs to flex and extend completely, like frog legs, to produce the best leap possible.

No Such Limitations in the Hind Limb
Simply leaping (or running and leaping) gets the job done so much better than an exaggerated pushup. Like birds, pterosaurs used their wings to flap and fly. That thrust can be employed during the initial hind limb leap, but not during the initial forelimb leap.

Leaping Lizard
If you want to have a good laugh while watching a rather ordinary lizard leap 3x its body length, check out this YouTube video. Just think how far a pterosaur could leap with those much longer frog-like hind limbs and elongated hips providing power at the femur, the tibia, the metatarsus and the toes in coordinated fashion, accentuated by powerful thrust provided by large flapping wings.

References
Clark J, Hopson J, Hernandez R, Fastovsk D and Montellano M. 1998. Foot posture in a primitive pterosaur. Nature 391:886-889.
Kellner AW, Costa FR, and Rodrigues T. 2012. New Evidence on the pteroid articulation and orientation in pterosaurs. Abstracts, Journal of Vertebrate Paleontology.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
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

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10 thoughts on “Scathing Book Review – Pterosaurs (Witton 2013) – Dimorphodon problems

  1. Is there any way this pterosaur could complete a pushup that would launch it into the air high enough to unfold that big wing finger before crashing to Earth.

    A good question.

    For a few pterosaurs other than this one, Habib and Cunningham have answered it doing, y’know, actual math.

    I see no math here – no attempt to figure out what forces the animal could generate and what it would need for a quadrupedal or a bipedal takeoff. This is not science.

    What I do see is that you misrepresent the scenario. Your Dimorphodon moves its wing fingers downwards while it’s pushing off. The idea is to keep them folded till the push (a downstroke) is finished and the next downstroke begins.

    • The wing finger opens automatically as the elbow extends. Like birds, only different. Moreover Mike Habib explained to me in his view the wing finger doesn’t have to open 180 degrees after launch as it is in the process while launching.

  2. Your Dimorphodon animation is nothing more than an argument from incredulity. You aren’t providing any mathematical calculations that go against Habib’s and Cunningham’s (i.e. data), you are just saying that you can’t visualise quad launch and therefore it cannot be so. This is not scientifically or logically valid.

      • But the wings do not need to be working earlier if the necessary thrust is provided to launch the body along a trajectory during which the wings can later unfold (not just for pterosaurs either, many modern birds only unfold their wings after they start to fall along their initial projectile trajectory). The maths have already been done and unless you can provide another set of biomechanical data and calculations demonstrating something contrary, your “alternate solution” will still remain a lavishly illustrated argument from incredulity. So yes, you can help me more, but it will involve specimen-based research, and a lot of physics, maybe CT scanning, force simulation, muscle reconstruction, and calculus, and to top that off, you might not like the end result. Without a robust method behind the testing and the arguments, this is all scientifically meaningless.

  3. I’m not Hercules.

    My ideas are based on data. Let’s wait for those launch tracks. And don’t forget the scaling problems. Desmodus is much smaller than Dimorphodon and Quetz. In the meantime please take a look at that YouTube video featuring a bipedal lizard from the Jayne lab. It’s pertinent. And it’s super fast.

    Pterosaurs are secondarily quadrupedal, which means they were basally bipedal and leaping with hind limbs, like Sharovipteryx, for instance. Also take a look at MPUM 6009.

    It’s not just the bones, which do get large in the forelimbs of derived pterosaurs, but the muscle mass supporting the hind limbs, which has been underplayed. Hind limb launch gets those forelimbs flapping and producing thrust along with the hind limb leap/dash. The forelimb delays the deployment of the forelimbs a little to late in my opinion.

    Habib is going to break down tenth of a second by tenth of a second, the actions he proposes. Let’s see if that still makes sense when that becomes available.

    • “The forelimb delays the deployment of the forelimbs a little to late in my opinion.”

      Just. Stop. Now. Science is not about opinions. If you are going to be making claims you better have every bit of data in place. If you’re not Hercules, you’ll have to work out enough until there are no heavier weights at the gym that you can’t lift.

      Everything you’ve been saying, maybe it sounds different to you, but to the rest of us, sounds like an incredibly elaborate “I can’t envision it, therefore it could not happen.”

      The running lizard is not pertinent enough. An organism can have the same bones and muscles, but if those bones and muscles have a radically different structure, the organisms they belong to need to be treated on their own terms. The structure and physics of the elements involved must be examined. Even slight changes in the position of a muscle or the shape of a bone can have profound changes in locomotion. You can’t get from that lizard to pterosaurs without doing the maths.

      As far as launch tracks, ok, let’s wait, but I wonder how you will take the evidence if, just if, you are shown to be wrong.

  4. I see you salivating at the thought of me being wrong… but I’ve changed many things on the site and blog as the best data comes in. I have no problem with change. I do have a problem with bizarre and unduplicated 35 mph forelimb launches on anything bigger than Desmodus.

    • You just don’t get it, do you? I am not “salivating at the thought of being wrong”, I am concerned about the air of absolute confidence you hold when you dismiss every pterosaur worker as wrong on every count whilst employing very shaky reasoning and methodologies.
      Maybe everyone is wrong and you’re right, that’s always a possibility, but if that’s the case, your evidence needs to be to be very solid and backed up several times over with different lines of evidence. Until I see a mathematical calculation that runs contrary to Cunningham and Habib, until I see more than an animation and the claim that being unable to visualise something makes it false, then it would be wise not to make such grandiose claims to know some great truth that only you are privy to and the rest of the world seeks to suppress.
      You say that you have changed your views, but I rarely see you admit to it. Furthermore, those views that you no longer hold, you once held them with the exact same absolute confidence that you hold your newer, yet equally tenuous views with. You use what to everyone else looks like the exact same methodology to derive your evidence now that you used then, despite it giving you varying results. I would like to know, in objective, methodological terms, what is the difference between what you are doing now compared to what you were doing then, and how you can justify its repeatability despite nobody being able to reproduce your results, and you producing unbelievably variable results.
      Numerous people have generously offered input on cladistic analysis, physiology, biomechanics, evolutionary theory, logic, and philosophy of science, and every time you have dismissed it or pretend like you never saw it. This ‘everyone else is wrong’, ‘me against the world’, ‘fount of absolute truth’ attitude is precisely what irks so many of us, not the possibility that, e.g., pterosaurs are lizards or that pterosaurs did not launch from their forelimbs. The hypotheses are only peripheral to the matter at hand, i.e., your methodology and attitude towards other scientists. It is good to have hypotheses that go against the grain, but also be aware of what science demands from its evidence. It must be as solid as possible, free of logical or mathematical faults, with reliable, repeatable testing performed as directly upon the object of inquiry as possible. And the scientist must hold him or herself with humility and acceptence that science exists beyond the scientist, that there will always be a possibility of being wrong, and that there are other scientists with different backgrounds, strengths, and insights.

  5. I don’t see any leeway here for an alternate hypothesis in your view. Just because the math is over my head, and likely over many other heads, doesn’t mean the calculation might be off, perhaps missing some important factor. For instance, earlier Habib thought the power came from the snap of metacarpal 4 against the substrate. He cheated the three fingers to make them smaller, not realizing metacarpal 4 doesn’t contact the substrate. What part of that has changed?

    And that’s not even the critical factor from both sides of the argument.

    You think I have dismissed all suggestions for improvement. Not so. I have only dismissed the bad and Herculean suggestions. Then there are my suggestions for taxon inclusion. Which scientists have adopted those? Why aren’t you chasing after them?

    Finally, I appreciate your readership. Let’s just see what happens in the future.

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