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Ask Mark Witton; Pterosaurs and more…

I contacted Mark Witton, author of Pterosaurs, which I’ve been reading with some artist-centric questions about his book. Mark’s been great in answering, but I think we’re both a bit too busy at the moment, so this is much more a dialog than an interview. My intention was to take advantage of Mark’s artistic abilities to ask questions visually… feel free to add questions or comments.

Interpreting skeletals…

How should your skeletals be interpreted? is there any fore-shortening or are they – as I suspect – constructed on flat plans? There are a few places where this makes for potentially large differences of interpretation… as in the hand digits, the humerus and the femur.

Mark Witton: The diagrams are on 2D planes. I think the takeoff pose used in them reduced most aspects of foreshortening, as the arm, for instance, is extended to the point where all the limb bones are more-or-less operating in the same plane. This, of course, wouldn’t be the case if the limbs were folded up tightly, because pterosaur limbs – the forelimbs in particular – don’t work entirely uniaxially.


The uropatagium…


Your book gives a thorough idea of what parts of the pterosaur anatomy are open to interpretation… except the uropatagium. You draw it unattached to the tail on page 52 (left). I’m biased: it looks like a baggy squirrel suit for RedBull stunt divers. The tail-attached version feels like a real animal design. You point to papers talking about the toe and thigh attachment but not – despite ALL THAT SPACE on page 55 – anything about the tail. What’s the hard knowledge on this? a) Are there biases in the evolution (ie. probability of a membrane forming between along tail edge vs between tail and ass)? b) Are there aerodynamic considerations… wouldn’t the attached version allow for more finely-tuned flight control? The unattached version would require leg movements to alter the uropatagium’s position, but the legs are also defining the main wing surface.

Mark Witton: I guess I did forget to mention the relationship of the tail to the uropatagium. This is probably because – despite what you see in many reconstructions – there is no evidence that the tail is incorporated into the uropatagium in any pterosaur fossil. The only good uropatagium we have preserved in an early pterosaur (actually, perhaps in any pterosaur) belongs to the holotype of Sordes, in which the tail is markedly deflected laterally without any affect on the symmetry of the membrane. This is presumably because the tail was not attached to the membrane at all (this is reflected in the illustration of wing membrane distribution in chapter 5 of my book, showing a long tailed pterosaur with the tail skewed to the left). Indirect evidence for a lack of tail incorporation in early pterosaurs stems from anuronathids. These taxa have long fifth toes, which are almost certainly reflecting a broad uropatagium, but many anurognathids have very dumpy tails which cannot, for obvious reasons, be operating the posterior membrane. So yes, there may be good mechanical reasons to think the membrane was attached to the tail, but there’s no fossil evidence for it. Unwin and Bakhurina’s (1994) work on Sordes uropatagium remains the seminal work on this issue.

 As for the space on page 55, that’s up to the typesetters, not me! I could only work by my word counts and figure numbers (the former of which was already blown out of the water). If I’d have known there was free space, I’d certainly have made use of it.

The uropatagium (cont’d)…

I tried to model the uropatagium in a rough 3D sketch. I modeled a body and tail form from your skeletals, then tried three different uropatagium variations: attached, free and a partial attachment somewhere along the base of the tail. Posed as in your skeletal, there’s not much chance of getting the free version to work out (middle above). It would have to move way down to the dorsal surface, which would kill any aerodynamic function. I had to bend his tail up just make it look half-way functional. At the very least, the tail would be pressed against this u. surface much of the time. The other two versions seem more plausible imo. Sound right?

Mark Witton: I think the reason you were having trouble fitting the tail over the top of the uropatagium is that the tail base is far too thick. Check out the caudal myology reconstructions of Rhamphorhynchus by Scott Persons: http://pterosaur-net.blogspot.co.uk/2013/01/guest-post-dragon-tails-what-pterosaurs.html

There’s virtually no muscle on them whatsoever, even at the base. The characteristically big caudofemoralis of most archosaurs is all but gone. The tail is essentially a bony rod with a slither of soft-tissue around it, and would probably easily extend above the uropatagium without impacting on it. I also note that the membrane in your diagrams is does not connect along the midline of the leg, but is dorsally deflected. I don’t think any fossils show us exactly where the membrane attached with respect to the midline of the leg (some experts in animal flight may have some ideas, though), but this may also be influencing the intrusion of the tail into the uropatagium.

More soon! (‘soon’ paleontologically speaking)

Mark Witton; Pterosaurs has arrived!

My day was turning out to be the shitty culmination of a shitty week, when – dingdong! Mark Witton’s Pterosaurs alighted at my doorstep. What a beauty! I’m far from capable of reviewing it as I’ve only read the first 3 chapters (in about as many minutes), but it’s safe to say that my day is saved. More feedback later, but here a two-pointer spoiler for those of you anticipating your copies:

Mark has a gift. He presents the uncertainties of science but never shies away from making his opinion clear.  With historical cases, he complements via omission, neglecting to name the workers behind outlandish ideas, while highlighting those who were precociously on the mark. With more modern workers, he presents the ideas with open sympathy, even when discussing Peter’s hypothesis, only to summarize point for point why it seems “the most unlikely hypothesis currently under consideration”.

Similarly, he respects the complexities without allowing them to clump up the text. In a subnote, he writes: “I’ve stuck with the term “protorosaurs” at the time of writing, for the sake of brevity and readability. Readers are invited mentally substitute something like “nonarchosauriform archosauromorphs” for every use of “protorosaur” if they feel like being more taxonomically savvy.” Of course, I will now spend the rest of the week trying to slip “nonarchosauriform archosaromorph” in as many casual conversations as possible. How cool is that?

Again, Mark has a gift, and I say this as someone who never tires of telling people that anyone can draw assuming that they do, in fact, draw. Mark isn’t the craftiest of illustrators, but I wouldn’t change a single of his drawings for any pile of slickness. Mark understands illustration, and he illustrates. As opposed to visualizing. He presents a scribbled Pteranodon longiceps historically hanging off a cliff, and the reader – without reading – immediately understands that this is illustrating an outdated concept. More than any other artist currently working with palaeo subject matter, I feel mark makes use of illustration to show what might have been, instead of purporting to visualize what was. This has to do in part with a twinge of naivety in his style, but I suspect is much more indebted to the wealth of knowledge that is assessing his every pencil stroke before, during and after his hand draws it out.

I can wholeheartedly recommend the book already, but I have to return to the shittiness of my other activities. More later, if you’re interested. Leave a comment.