More Than Just a Pretty Propatagium

The CAGS specimen CAGS IG 02-81 originally attributed to Dendrorhynchoides (Lü et al. 2006, 18 steps different) and then to Jeholopterus (4 steps different) is neither genus, but has a suite of traits that distinguish it from both. But that’s not the point of today’s blog. We’re looking today at what appears to be an extraordinary propatagium unlike any other (Figure 1).

The CAGS specimen

Figure 1. The CAGS specimen attributed to Dendrorhynchoides and then to Jeholopterus, but is distinct from both. Note the dark triangle that appears to be a fibered propatagium (between the wrist and shoulder) more distinct than the remnants of the brachiopatagium.

A Propatagium with Aktinofibrils?
The apparent propatagium of the CAGS specimen appears to preserve all the traits of a brahiopatagium, which is unlike that of any other pterosaur. For instance, it has aktinofibrils! Elgin, Hone and Frey (2010) considered this an example of dermal shrinkage in the wing membrane. Actually the membranes are torn and folded without shrinkage. So, this is yet another one of Nature’s tricky illusions (like Sordes) deserving of a more vigorous examination.

Interpretation of bony and soft tissue elements in the CAGS specimen.

Figure 2. Interpretation of bony and soft tissue elements in the CAGS specimen. Click to see rollover image. The actual propatagia are in blue. Torn and displaced brachiopatagial elements mask both propatagia. The parts marked "distal wing elements" are below the more superficial skeletal elements. As in other anurognathids, the distal wing elements were folded over the back, so here in ventral exposure, they are preserved deeper than the rest of the skeleton after dislocation. Can you find the sternal complex? I probably underestimated the preservation of wing membrane here, much of which is beneath the body. The pteroids are relaxed here.

Layered Membranes
As you might have guessed from the title of this blog, there’s more to it than meets the eye. DGS (digital graphic segregation) enabled the separation of this odd bit of anatomy into two separate overprinting layers. One is indeed the propatagium, essentially devoid of internal details as in other pterosaurs (perhaps because it is the extensor digitorum longus as blogged earlier). The other is  a torn section of the brachiopatagium, the part of the wing with all the aktinofibrils. The apparent lack of distal wing phalanges indicates parts of the wing were torn off their phalangeal moorings. Using DGS clarifies the mystery. Critical analysis has to be done, rather than accepting face value.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Lü J-C, Ji S, Yuan C-X and Ji Q 2006. Pterosaurs from China. Geological Publishing House, Beijing, 147 pp.

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