Earlier here, here, here, here and here we looked at the new book, “Pterosaurs” by Mark Witton (2013) and the many problems, mistakes and oversights that book contains. Today we’ll look at how Witton attempts to support the traditional hypothesis of a deep chord wing membrane attached at the ankle (Fig. 1). We covered that topic earlier here.
When a bad hypothesis meets good data
Witton (2013) upholds the deep chord wing membrane hypothesis. So when excellent data indicates a shallow chord with fuselage fillet (the Stromer model, Fig. 8), Witton invents excuses for it (Fig. 1), calling it “dessicated” and “shriveled.” There are no other examples of desiccated membranes in pterosaur fossils. In any case, wing membranes contained little water in life, so how could they shrink when desiccated, especially when buried underwater? Adding to the confusion, on the same page (Witton 2013: 196), he illustrates a nicely preserved uropatagium and webbed toes from the same specimen. These, strangely enough, have not suffered at all from desiccation!
To clarify things
Peters (2002) published an image (Fig. 8) of what happens when the Vienna specimen unfolds its wings. Here it is animated (Fig. 2). Witton ignored this paper.
The real wings, based on the excellent data provided by the Vienna specimen, demonstrate the membranes were stretched between the wingtip and elbow, not the ankle.
Note: In all pterosaurs (Fig. 2) the wings were functionally disconnected from the hind limbs (contra the traditional view upheld by Witton), which means pterosaurs would have no trouble running around on the ground, bipedally or quadrupedally.
Witton (2013) misinterprets the pterosaur wing membrane
Earlier here and elsewhere we looked at the true shape of pterosaur wing membranes. Unfortunately, Witton (2013) promotes a completely different view. And this is not just a matter of opinion or sides in an argument. This fact vs. fiction (Fig. 1).
Upon seeing this image (Fig. 5) promoted as a great example of a narrow-chord wing membrane, Darren Naish considered this “ambiguous” because the specimen has no torso (Fig. 8). Why do you need a torso? You have the entire wing! And it follows the Vienna Pterodactylus (Fig. 1) configuration – narrow at the elbow (and the BRI 010 specimen, see Fig. 6!). There’s no trailing membrane here that – can – extend to the ankle (Fig. 8). There’s no example of such a wing membrane anywhere, except, to some eyes, in Sordes. But that was demonstrated to be due to a disarticulated radius and ulna, which can be identified in the fossil.
Now, just to be fair and open,
Helmut Tischlinger kindly sent me a short paper (Monninger et al. 2012) describing a new Rhamphorhynchus specimen BRI 010 (Fig. 6), in which “a linear structure runs along the trailing edige from the ankle to the tip of the wing finger.” That’s exciting. If verifiable, this would support the Witton model. Unfortunately, requests for hi-rez images of this specimen have gone unanswered. But I can present the image in low resolution from the abstracts, which are available online.
Even at low resolution
we can tell that this is a Rhamphorhynchus with a well-preserved wing membrane with a trailing edge directed precisely at the elbow, as in the darkwing Rhamphorhynchus. Unfortunately the ankle has swung forward to the elbow. If the narrow-chord wing is correct, then this image needs no further explanation. If the deep-chord wing is correct we should see some sort of bending or curving toward the knee of the trailing edge (as shown in Fig. 3), but there is none.
By the text of the short paper I thought I was going to have to apologize to the pterosaur experts.
Linear structure on the trailing edge?
I can’t comment on the linear structure along the trailing edge, having never seen one, but then I haven’t seen this specimen in high resolution either. We’ll have to wait.
As part of the leading edge, the propatagium and pteroid are also important aspects of the pterosaur wing. Witton (2013) ignored the evidence and his own text that the pteroid articulated with the proximal carpal (radiale) and instead sometimes illustrated it in the cup of the preaxial carpal (Fig. 7), sometimes locating it on the radiale, sometimes on the distal carpal. His text does report the preaxial carpal articulated with the distal carpal, so why the imprecision? Witton reports the pteroid “probably articulated in a depression on the medial side of the preaxial carpal (Bennett 2007) and MAY have also contacted the proximal syncarpal (Peters 2009).” Actually, with the way the wrist bent, the pteroid would rarely if ever contact the preaxial carpal. They diverged from one another and were separated by the length of the proximal and distal carpals.
Witton did not report the pteroid and preaxial carpal were present on Cosesaurus (Peters 2009), first observed but misidentified by Ellenberger (1993) who, unfortunately, flipped that manus over in order to have digit 2 longer than the lateral digits.
Anyway, a series of errors over time ultimately brings us to the truth of what is actually happening with the wings of pterosaurs, a configuration first envisioned by Stromer in 1910 (Fig. 8b).
Monninger S, Frey E and Tischlinger H 2012. Supporting structures in the flight membrane of pterosaurs. EAVP abstracts, Teruel, España. Royo-Torres, R., Gascó, F. and Alcalá, L., coordinators. 10th Annual Meeting of the European Association of Vertebrate Palaeontologists. ¡Fundamental! 20: 1–290.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.