What is happening between the legs of Sordes?

The hind limbs and soft tissues of Sordes.

Figure 1. Click to enlarge. The hind limbs and soft tissues of Sordes. Above, color-coded areas. Below the insitu fossil. Pay no attention to the little Sordes-like impression beneeath the right foot. It is likely an illusion. The disarticulated ulna and radius are not indicated here.

The Problem
The holotype of Sordes (Sharov 1971, Fig. 1) presented lots of interesting soft tissue preservation, including hair, wing membranes and uropatagia. Unwin and Bakhurina (1994) further described the various soft tissues, promoting a unique structure, the uropatagium, which they reported as a membrane stretched between the hind limbs and pedal digit 5 tips, without contacting the tail. They also reported the wing membrane had a deep chord with a trailing edge that contacted the ankle.  Unfortunately not much detail has been published on this all-important area to demonstrate these observations. Both published illustrations were mere small outlines with Sharov (1971) adding texture and Unwin and Bakhurina (1994) adding halftone dots.

What Are People Seeing Here?
In Figure 1 The soft tissues at the margins of these soft tissue structures are clear to see. Unfortunately, these soft tissues do not continue to contact the legs, either medially or laterally. In fact, there appears to be a large open space between both legs and the tail. Earlier workers graphically filled in these areas. The question is: is there more soft tissue impressed in the matrix in these open spaces? Or is that just the matrix itself?

An Alternate Proposal
Earlier I noted here and here that the right wing was largely complete and preserved a narrow chord wing, narrow at the elbow with a fuselage fillet. The ulna and radius of the left wing appear to be disarticulated and drifted posteriorly. The green area (Fig. 1) appears to be disarticulated wing membrane, twisted and folded, starting left of the left leg and continuing between the legs. No other pterosaur uropatagia are this substantial, this structured and this shape. So, what is the correct interpretation?

The alternate model has not been criticized, but it has also not been accepted. I’d like those who hold to the traditional model to produce some sort of interpretation of the various hair balls and membranes like the one above (Fig. 1). The Sordes holotype has colored so much thinking about pterosaurs that it would be GREAT if someone could translate this fossil in detail for a better understanding. OR, if someone could come up with just one more example of a wing membrane attached to the ankle with a single uropatagium spanning the hind limbs.

I’ve been waiting for this since 1994. Let’s not be shy now. Words won’t cut it. Cartoon outlines won’t cut it. Bring out the hirez tracings with circles and arrows and let’s settle this issue.

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.

Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeonntologica Polonica 56(1): 99-111.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277–301.
Sharov AG 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

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