Scathing book review – Pterosaurs (Witton 2013) – finger mistakes

Earlier here and elsewhere in this blog we looked at the various mistakes and oversights promoted by Mark Witton (2013) in his new book, “Pterosaurs.” Today we’ll look at the configuration of the three free fingers and the many problems with Witton’s proposed configuration (Fig. 1).

Figure 1. Here Witton promotes the idea that pterosaur metacarpals were pressed back to back with the palmar side anterior, the pteroid articulating with the preaxial carpal and the elbow overextended.

Figure 1. Here Witton (2013) promotes the idea that pterosaur metacarpals were pressed back to back with their palmar sides anterior, the pteroid articulating with the preaxial carpal and the elbow overextended. None of these are supported by fossil evidence. 

Witton (2013) promotes the traditional idea that the dorsal surfaces of the three free fingers were appressed to the anterior surface (the former dorsal surface) of the axially rotated metacarpal 4. This means the free fingers would be oriented palmar side anterior during flight (Fig. 1) and extended palmar side ventro-posterior during terrestrial locomotion. Such a configuration  allows no room for the extensor tendons, especially the big one for the wing finger (Fig. 2). Moreover, posterior fingers do not match known pterosaur hand ichnites.

The actual orientation and configuration of the three fee fingers is shown below (Fig. 2).

Figure 2. The hand of the most primitive pterosaur with only metacarpal 3 attached to metacarpal 4. This provides room for extensor tendons. It also enables lateral finger extension during terrestrial locomotion and medial grappling during tree clinging. Crushing rotates the unguals anteriorly in this case. The extensor tendon process would bang into digit 2 when fully extended in the Witton model.

Figure 2. The hand of the most primitive pterosaur with only metacarpal 3 attached to metacarpal 4. This provides room for extensor tendons. It also enables lateral finger extension during terrestrial locomotion and medial grappling during tree clinging. Crushing rotates the unguals anteriorly in this case. The extensor tendon process would bang into digit 2 when fully extended in the Witton model.

The actual configuration is supported by evidence.
The present configuration provides room for the extensor tendons and permits the extensor tendon process to move unimpeded whenever fully extended in flight. With the free fingers facing palmar side down, like all other tetrapods, during terrestrial locomotion the fingers would extend laterally, matching ichnites. During tree clinging the fingers would grapple medially rather than, as Witton proposes, opening anteriorly, in a “begging” configuration.

The metacarpal “drawbridge”
The connection between metacarpals 3 and 4 produces a hinge. That’s why the metacarpus sometimes swings up during taphonomy to give the impression of the configuration that Witton proposes, as if the “drawbridge” was raised.

Pterosaur-fingers

Figure 3. Pterosaur wrist and hand images from Witton (2013). Neither demonstrates the palmar side forward configuration. The lower Pteranodon image is in posterior view and the stacking of the metacarpals is therefore anterior, away from the viewer, as in the Peters configuration. The wing finger of the Pteranodon would have been in the Z-axis, toward the viewer, but it was disarticulated during burial. Bennett (1991, 2000) thought metacarpal 4 was axially rotated during taphonomy. Not so. Green = flexor tendons. Red = extensor tendons.

So, where did Witton get his configuration?
From Bennett (2008), and this Santanadactylus specimen (Fig. 4, ignoring, apparently all others).

Santanadactylus hand and fingers

Figure 4. Santanadactylus hand with metacarpals preserved at a 45 degree angle to the anterior face of metacarpal 4. This demonstrates the drawbridge effect in which Bennett elevates metacarpals 1-3, raising the drawbridge. Actually, the drawbridge was down in life. Imagine what would happen to fingers 1-3 when the wing finger was extended! And where were the extensor tendons? Only lowering the drawbridge solves all these problems.

The Santandactylus specimen preserves metacarpals 1-3 raised, like a drawbridge to about 45 degrees, but this is a taphonomic artifact. Bennett’s (2008) configuration further raised the metacarpus to appress against metacarpal 4, palmar side anterior. Peters’s (2002) configuration lowers the metacarpus on its hinge, palmar side down. This provides room for the large extensor tendon and the extensor tendon process of the wing finger when it is fully extended in flight. This also matches all undisturbed pterosaur fossils (Fig. 2).

Added note:
I’m hearing that my notes hear are not swaying the experts. Please see the conversations below and check out this link to pterosaur finger flexion.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.

Advertisements

8 thoughts on “Scathing book review – Pterosaurs (Witton 2013) – finger mistakes

  1. This article should not be titled ‘Scathing book review’ – I think that this is massively dishonest of you, presumably done as an effort to get people to visit your site. It should be titled ‘My alternative interpretations of what professional scientists have said’, seriously.

  2. It – is – an alternative interpretation, evidence based. I show evidence to back up my position for every problem in the book. And there’s more to come. Your support of Witton’s misinterpretations is astounding. And, just to be fair, Darren, you are still invited, as you always have been, to have a discussion about anything in particular. Let’s do it via email.

    BTW, there is no profit in more people visiting my site, except, perhaps, to expose them to alternative interpretations. And the numbers haven’t jumped.

  3. If you are implying that I’m supporting Witton for any reasons other than those linked to assessment of evidence, well, you’re wrong. My point here is that it is utterly dishonest and unfair of you to title your articles ‘Scathing book review’ when all you’re doing is saying “I disagree with what all other pterosaur workers say about everything, because I have my own unique interpretations of the evidence”. As per previous discussions, you miss or ignore the point that I (and, I think, all of my colleagues) disagree with your interpretations because we find them wanting or erroneous, not because we’re idiots who slavishly adhere to tradition and the literature for the sake of it.

    As for the specifics of this article – no, I don’t think you’re right at all. As Bennett and Witton argue, pterosaur fossils show, again and again and again, that the ‘ventral’ (= flexor) surfaces of the free digits were indeed directed anteriorly, not ventrally as you’re saying, and that the metacarpals are indeed ‘stacked’ vertically against mcIV. You simply assert that Bennett (2008) was unable to see taphonomic distortion when, in fact, there’s no evidence of this; furthermore, he effectively demonstrated that the ‘palmar surface faces anteriorly’ is not a problem as goes the musculature and ligament anatomy. Readers should know that your assertions are simply assertions – nothing more. As goes the trackways, it’s misleading to imply that there’s a problem: animals can move their limbs at the shoulder and elbow joint and we have good reason to think that pterosaurs could easily achieve a posture that matches the tracks.

    Your criticism of Witton thus reflects your own adherence to a pet hypothesis that appears to be erroneous: Witton is not wrong nor worthy of “scathing” criticism here.

    Bennett, S. C. 2008. Morphological evolution of the wing of pterosaurs: myology and function. Zitteliana B 28, 127-11.

  4. Wow. I am totally amazed that evidence means nothing to you.
    To your point, we can match pterosaurs to tracks, indeed. They just don’t put their fingers so far out in front of their shoulders that the only thrust vector is backwards.
    And the palmar surface anterior … you really think that provides room for extensor tendons and all the other things pterosaurs need and do? I looked at Bennett 2008 here:
    https://pterosaurheresies.wordpress.com/2011/08/22/which-way-did-pterosaur-fingers-flex/
    His digit 3 was dorsal in one drawing, ventral in another. Let’s play that as digit 1 was supposed to be dorsal. And in the anterior view his extensor [slight modification here] (= flexor because Bennett reversed those) tendon 4 rode ventral to the stack of metacarpals 1-3 as they adhered to metacarpal 4, even though the extensor tendon actually rotates right into the middle of the stack (although Bennett 2008 adjusts that ventrally). And let’s hope that in those pterosaurs in which metacarpals 1, 2 and 3 in sum were deeper than metacarpal 4 the extensor tendon had the good since to somehow go around them. And let’s hope that pterosaurs only had to flex their fingers once in their lives, because where their extensors would have been, they were glued to metacarpal 4. And why do all the basal pterosaurs, preserved undisturbed in situ have their drawbridges down? That goes for Pteranodon too. See images above and elsewhere.

  5. Wow, I am totally amazed that you think that your pretty pictures and some vague assertions can be imagined as “evidence” to you. Quit it with the “drawbridge” thing – comparisons like this are not helpful, I actually have no idea what you mean. I think you’re correct that Bennett (2008) seems to show digit I as ventrally located in ONE of his diagrams (his Fig. 3, p. 132), but it doesn’t destroy his point, nor is he inconsistent elsewhere in the text or diagrams. In flattened pterosaurs, metacarpals I-III sometimes look as if they’re not overlapping but 3D specimens show that they are, the tendon for the wing-finger apparently passing ventral to the metacarpal I-III bundle. I’m partly basing this on a 3D wrist region I was working on some years ago.

    My main point remains, which is that – even in cases such as this, where there is some ambiguity – you are misleading naive readers by claiming that you have the ‘right’ interpretation. Above, you say stuff like we look at the “many problems with Witton’s proposed configuration”. Again, I think it’s more likely that Witton is right and that you’re wrong.

  6. Ventral indeed. I modified my earlier reply when I double-checked the lit.
    Let me help you with the drawbridge thing. Primitively the palmar side is down in tetrapods, and that includes birds, bats and pterosaurs in flight. In my view only metacarpal 4 rotated axially so that its palmar side was posterior for wing folding. Metacarpals 1-3 stayed put because they were being used in tree clinging and terrestrial locomotion where a ventral orientation in flight becomes a medial orientation, when the arms are ventral, like clapping. Hyperextension from this configuration gives you lateral finger tracks. The posterior #3 trace comes from a spherical metacarpophalangeal joint. You don’t see purported “evidence” of metacarpals 1-3 rotating up on the 3-4 hinge until metacarpal 4 gets really big in derived pterosaurs. That’s the drawbridge thing. The 3-4 connection is a hinge. With soft tissue rotted away, that hinge is free to rise and fall. By the way, the hinge rotates down when the preservation is flipped (see the holotype of Eudimorphodon).

    In Bennett’s view the entire hand supinated, raising metacarpals 1-3 to the new dorsal surface of metacarpal 4. Then or concurrently metacarpals 1-3 slid back to resume an anterior position, then glued themselves to the new anterior face (the former palmar face) of metacarpal 4. Of course, this breaks the metacarpal 3-4 connection (remember the old anterior surface of metacarpal 4 is now the new dorsal surface and metacarpal 3 is now located at the new ventral rim of metacarpal 4). Now the large extensor tendon is forced ventrally, but the extensor tendon process did not follow the extensor tendon ventrally. It stayed in the middle, where the fingers slid to. So, evidently there was a slight detour once it got around the fingers, which isn’t good engineering. Bennett’s scenario is so convoluted it’s a fairy tale. And I didn’t even bring up the fact that he promotes a knuckle-breaking reversal of flexion and extension. Well, there I did. If -I- had come up with this scenario you would have been well within your rights to have me pilloried.

    Darren, you have a fossil record in Cosesaurus in which a pteroid, prepubis, uropatagia, arm fibers, antorbital fenestra, strap-like scapula, stem-like coracoid, broad sternum in contact with the crossbars of the interclavicle, attenuated tail, elongated ilium, 4 sacrals, elongated pedal 5.1 etc, etc. are all present and yet there’s nothing else odd about its metacarpal arrangement. Cosesaurus has frilled hands that flap, but it doesn’t have wings. Disagree with half or most of this and you still have a damn good ancestor for pterosaurs. On the other hand, Bennett had to invent his ancestor from thin air. Again, if roles were reversed and -I- had invented an imaginary creature when a real one was known… well, I think you get my point.

    There’s no ambiguity. I encourage you to try your various configurations in various poses with a 3D specimen and let me know what you get. Furthermore, if you can find one small pterosaur with a small metacarpus that has metacarpals 1-3 pasted onto the anterior face of metacarpal 4, please bring it to my attention. I know of none. Currently, you’ll note that when the finger unguals point anteriorly in situ, there is always an interphalangeal break forced on it during crushing or rotting. And take another look at that Pteranodon above. It’s a great example in which the anterior face of the hand was buried first, retaining the anterior order of the fingers, with #1 deepest and the others higher in the stack. If it was preserved in the Witton/Bennett configuration we would not see this stacking, but all three would be side by side. Right?

  7. Will try and be brief in responding here, sorry if that sounds rude. Rotation of mcIV: I’m familiar with your ‘twisted wing-metacarpal’ model, but Bennett did a good job of showing that it’s not a good explanation (after all, it would necessitate twisting of the tendons as well, and that clearly didn’t happen). Your other stuff is very hard to follow – note that it’s unnecessarily insulting to refer to Bennett’s stuff as ‘a fairy tale’ – – err, did you re-read the ‘just-so story’ you just provided (the drawbridge stuff) before saying that? The point is that, whether we ‘like’ Bennett’s interpretation or not, it fits as a good explanation of what we see: digits I-III and their metacarpals are typically preserved overlapping, showing that they were indeed ‘stacked vertically’ as per what Bennett and Witton say, even in forms with a short metacarpus, including Anurognathus and Eudimorphodon. And they’re preserved this way in 3D specimens! So, you’ve decided to ignore all criticism of your ‘with a twist’ model and are just carrying on regardless?

    Cosesaurus: like virtually all of your stuff, the ‘pterosaur-like’ characters that you’re reporting are not reliably present in the actual fossil. As you know, your claim that pteroids, prepubes, uropatagia and so on are present in that fossil are _totally_ unconvincing and I’m sure that they’re another artifact of your magic-eye technique — I have to assume by now that you can appreciate this. Cosesaurus does not “have frilled hands that flap”. It might in Petersland, but there’s no reason for the rest of us to take this at all seriously. Really, come on.

    While I’m here – are you posting stuff to ‘Before Its News’ now? If you are, you shouldn’t.

  8. Earlier I noted that Bennett’s flexor and extensor tendons do not cross his dorsal and palmar carpals, like they do in all tetrapods. So that’s a problem on top of all the others. UNLESS the anterior surfaces of the preaxial carpal and pteroid are the former dorsal surfaces of the centralia (which is true), but then all the other carpals haven’t moved. But then, no centralia anchor tendons… So that’s one reason why Bennett sees odd twisting when you axially rotate metacarpal 4. What other criticisms of the twist are you referring to? I know of none. I addressed Bennett’s criticism in a manuscript that was rejected. I also addressed Bennett’s criticism online. I will be working on this again this weekend as appressed metacarpals may change things.

    You haven’t addressed the disconnection and migration of metacarpals 1-3 required in Bennett’s supination hypothesis. I know it’s tough, but that has to be addressed.

    Please provide a diagram of a “stacked vertically” metacarpus in a basal pterosaur. Verbage isn’t cutting it. Witton’s own illustration of Rhamphorhynchus demonstrates my view with a twisted mc4 and only mc3 attached to mc4, as in all other tetrapods.

    re: Cosesaurus: Ellenberger saw those hard and soft tissues before I did. Please refer me to another in detail examination of Cosesaurus that supports your position. I know of none. The stem of the 2mm prepubis is one of the strongest impressions in the fossil.

    re: Before it’s News – they asked for RSS feeds and I granted that to them.

    And to you, Darren, on a personal note, when you say that nothing is correct in my tracings of Cosesaurus, or in any of my 720+ blog posts, or in any corner of ReptileEvolution.com, (not to mention your support of c wing membranes, Bennett’s finger-cracking reversal of flexion/extension, and other strange ideas) brand you as a fringe character. Moreover if you’re the type who is unable to grant even a modicum of credit that won’t be seen in a good light either. Toss in a few kudos and you’re comments will be seen as more credible.

    If Cosesaurus is confirmed to be a good ancestral taxon by some future unbiased grad student, then you don’t want to be on the wrong side of history. And if not Cosesaurus, then Sharovipteryx, Longisquama, Kyrgyzsaurus, Pteromimus, Tanytrachelos, Macrocnemus, Langobardisaurus, Huehuecuetzpalli, etc. all better candidates than any archosaur(inform).

    It’s just such a landslide. How long can guys like you ignore and avoid this data? You can hate me and my methods all you want, but to toss out the best candidates for pterosaur ancestry because of their association with me is unwarranted.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s