The best ‘Sordes’ uropatagium… is another overlooked wing

This much talked about, but rarely seen ‘Sordes’ specimen
(Fig. 1), has been known for decades. It made a brief appearance some 30 years ago at an SVP talk by David Unwin where it caused quite a stir. I haven’t seen it again since.

Today this rare ‘tail-less’ specimen made another brief appearance
in an online Palaeontological Assocation talk “Resolving the pterosaur bauplan using a quantitative taphonomic approach” by Rachel Belben (2012, video link), one of Unwin’s students.

Not one, but two similar Sordes specimens
were presented by Unwin at SVP decades ago. Both appeared to have a distinct uropatagium stretched bat-like between the sprawling hind limbs (Figs. 1, 2). Everyone wondered whether that membrane was 1) above or below the cloaca, 2) attached or not attached to the tail, and 3) what sort of precursor taxa would gradually develop such a membrane controlled by hyperflexed lateral toes. In bats, of course, the vaguely similar calcar arises from the ankle. The toes are not involved.

Sharov 1971
first described and figured the Sordes holotype (Fig. 2, upper right) with a small drawing that appeared to clearly show a uropatagium stretched between the hind limbs and controlled by those odd Tanystropheus-like elongated lateral toes.

Unwin and Bakhurina 1994
brought this odd bit of flight membrane to a wider audience with a short paper in Nature. Their drawing (Fig. 2 middle right) paid less attention to detail.

Peters 1995
disputed the uropatagium, considering it a displaced wing membrane. That critical hypothesis was presented again in Peters 2002 (Fig. 2, left and bottom).

Elgin, Hone and Frey 2012
sided with Sharov, Unwin and Bakhurina, also paying little attention to the specimen.

Back in 2011,
the uropatagium of the Sordes holotype showed up here with another tracing (Fig. 5) that showed the displaced radius + ulna and its displaced membrane.

A new tracing of the rare specimen
(Fig. 4) shows the purported uropatagium extending far beyond the hind limb. That indicates a problem! This is not a uropatagium. Maybe that’s why we haven’t seen this rare specimen for 30 years. A closer examination reveals a series of pterosaur arm bones beneath the hind limb elements. Arm bones or not, this ‘uropatagium’ is a brachiopatagium, a wing membrane, complete with aktinofibrils (Fig. 5).

Adding what little is known
to the large pterosaur tree (LPT, 256 taxa) nests the rare specimen not with Sordes, but with the tiny flightless anurognathid PIN 2585/4 specimen that shares the plate with the holotype of Sordes, PIN 2585/3 (Fig. 2). We looked at that rarely seen specimen earlier here.

Distinct from the flightless PIN 2585/4 anurognathid specimen,
this one has large, robust wings.

In summary
this rarely seen specimen

1. is not Sordes
2. does not present a uropatagium
3. can now explain why a Sordes-like tail is absent here
4. evidently has never been carefully examined before
5. has fooled pterosaur experts for decades
6. is one source of pterosaur mythology that many pterosaur workers and their minions continue to believe in fifty years after its original description.

Someone please tell Rachel Belben
so she can wash her hands of this decades-old error and start fresh.

The Sordes uropatagium is a misinterpretation.
We need to bury this mistake and forget it. Stop promoting and believing this myth. It has been exposed.

References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeonntologica Polonica 56(1): 99-111.
Peters D 1995. Wing shape in pterosaurs. Nature 374, 315-316.
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.

wiki/Sordes