Bakhurina and Unwin 2004, an attempt at reconstructing the flight apparatus of a Triassic pterosaur

Famous for their deep chord wing membrane model
Unwin and Bakhurina (1994) were incredibly and regretfully influential for their Nature paper on Sordes, which essentially reposted Sharov’s (1971) observations of a deep chord wing membrane and a cruropatagium stretching between the hind limbs (not involving the tail).

At first glance it does look like Sordes had a deep chord wing membrane and a cruropatagium stretched between the hind limbs (Fig. 1). Unfortunately none of these three paleontologists realized the illusion of the depth of the wing membrane and the cruropatagium was caused by the posterior dislocation of the left ulna and radius. These bones brought with them enough wing membrane to get tangled around the ankles, which you can see here.

Another view
Peters (2002) noted that the wing membranes of Sordes were not as deep as Sharov (1971) and Unwin and Bakhurina (1994) had reported, due to geological faults misinterpreted as membrane borders. The dislocations of the ulna and radius were not noted then, but one of the faults included one of the bones of the antebrachium.

Figure 1. Basal pterosaur wing membranes based on the Sordes illusion, from Bakhurina and Unwin (2004).

Figure 1. Basal pterosaur wing membranes based on the Sordes illusion, from Bakhurina and Unwin (2004). Colors added.

Following the publication of Peters (2002) and eager to add support to their earlier observations, Bakhurina and Unwin (2004) reported on a specimen (MCSNB 8950) that Wild (1993) had attributed to Eudimorphodon. This is the specimen in which the pterosaur sternal complex was first observed to subdivide into four fused elements: two overlapping clavicles, an interclavicle and a sternum (Fig. 4). More to the point of this post, wing membrane soft tissue is also preserved (Fig. 2) in MCSNB 8950.

Top: image from Bakhurina and Unwin (2004). Middle: Key areas highlighted by  Bakhurina and Unwin (2004) that purport to show wing membrane edge on top of uropatagium (blue) and uropatagium directed toward metatarsal 5 (red). Bottom: highlighted areas placed back into the erased areas in the top image. These parts merely fill in missing areas of the wing membrane trailing edge. The uropatagia are not visible.

Figure 2. Top: image from Bakhurina and Unwin (2004) the wing membranes of MCSNB 8950. Middle: Key areas highlighted by Bakhurina and Unwin (2004) that purport to show wing membrane edge on top of the cruropatagium (blue) and uropatagium directed toward metatarsal 5 (red). Bottom: highlighted areas placed back into the erased areas in the top image. These parts merely fill in missing areas of the wing membrane trailing edge. The uropatagia are not delineated in their illustration. By their own account the  purported uropatagium does  not contact the tips of pedal digit 5. So why is it reconstructed that way in figure 1? fe = free edge of wing membrane according to Bakhurina and Unwin (2006). This appears to be a groove artifact like other grooves in the specimen and the illustration overemphasizes fiber differences.

For some reason, Bakhurina and Unwin (2004) cut out or erased parts of the wing membrane they considered important enough to enlarge and focus on (Fig. 2). When the enlarged regions are reduced and graphically returned to their original locations (using their own drawings) these areas of focus repair the holes and make it look like one continuous wing was present, as appears to be the case here (Fig. 3). They agree that a portion of the wing membrane spans the hind limbs by coincidence. They didn’t realize that much the same thing happened in the Sordes fossil.

Hoping to recapture the illusion of the slight V-shape in their uropatagium, Bakhurina and Unwin (2004) drew their “area X” as symmetrical as possible in closeup, even emphasizing the right right side a bit more. However, replaced into its original location, the asymmetry is strongly left (between 1:3 and 1:4), which adds doubt to their hypothesis.

Everywhere else uropatagia are paired and separate
In all pterosaurs, including MCSNB 8950 and Sordes, the uropatagia are paired, as in SharovipteryxThese two specimens (MCSNB 8950 and Sordes) are the only ones in which a cruropatagium have been observed (and only by Unwin and Bakhurin among all paleontologists). Both observations are readily dismissed with other more tenable interpretations (Fig. 3) that take into account dislocated bones and membranes due to taphonomy.

MCSNB 8950 colorized wings and uropatagia on the insitu fossil.

Figure 3. MCSNB 8950 colorized wings and uropatagia on the insitu fossil. Other than the uropatagia, which Bakhurina and Unwin ignored, this interpretation matches their own. They agree that a portion of the wing membrane spans the hind limbs by coincidence. Much the same thing happened in the Sordes fossil.

Here  (Fig. 3) is an alternate interpretation. The light blue is one continuous wing. The purple is the other wing. The green represents uropatagia. There are parallel scratches in the fossil. I don’t think it’s clear that the area below the line in the wing represents a different sort of tissue/fiber. Similar grooves define the uropatagia shown here (Fig. 3) in green.

MCSNB 8950 reconstructed and compared to the unrelated holotype of Eudimorphodon. The sternal complex is shown in various colors delineating its component parts.

Figure 4. Click to enlarge. MCSNB 8950 reconstructed and compared to the unrelated holotype of Eudimorphodon. The sternal complex of MCSNB 8950 is shown in various colors delineating its component parts. Unfortunately the skull is missing in MCSNB 8950. The distal wing and lower hind limb are missing in the Eudimorphodon holotype. Embryo pterosaurs demonstrate that if MCSNB 8950 were a juvenile, it would have been virtually identical to the larger taxon.

Bakhurina and Unwin (2004) interpreted the soft tissue of MCSNB 8950 as they had in Sordes (Fig. 1), as evidence for the mythological deep chord wing membrane attached to the lateral ankles and a cruropatagium stretched between the hind limbs and terminating on the tips of pedal digit 5. Bakhurina and Unwin’s own evidence does not demonstrate the continuation of the cruropatagium to the tips of pedal digit 5, but only, at best, to the ankles, as in other pterosaurs. Here (Figs. 2, 3, 5) this is demonstrated as a coincidence from displacement, as in Sordes (Fig. 5).

The paired uropatagia and displaced wing membrane in the holotype of Sordes pilosus.

Figure 5. Click to enlarge and see the rollover image. The paired uropatagia and displaced wing membrane in the holotype of Sordes pilosus. Note the area between the wing membrane and uropatagia is blank matrix, which argues against the Unwin/Bakhurina model.

Moreover, Bakhurina and Unwin (2004) made the same mistake as Wild (1993) in attributing MCSNB 8950 to Eudimorphodon, ignoring the disparate anatomy. In the larger pterosaur tree MCSNB 8950 nests as a basal anurognathid, alongside those with a robust tail vertebra, like Peteinosaurus, MCSNB 3359, another Triassic pterosaur. Embryo pterosaurs demonstrate that if MCSNB 8950 were a juvenile, it would have been virtually identical to the larger taxon.

Typical of Dr. Unwin, published work (Peters 2002) disputing Sharov (1971) and Unwin and Bakhurina (1994) was not cited in his reference list. So, this is a continuing problem when opposing views are not cited and tested. If opposing views are readily dismissed they should be, with evidence to the contrary. At present we can only wonder why pertinent published work was excluded. This demonstrates weakness in an argument if the opposing view cannot be explained away with better data, as it is here.

In Dr. Unwin’s view and in the views of many other traditional pterosaur workers, the twin uropatagia that are present in Sharovipteryx became sealed at the midline in basal (long-tailed) pterosaurs only to be split again in short-tailed pterosaurs like Pterodactylus. Everyone, including David Attenborough, has bought into this. As you can see from the above demonstration, this is an illusion.

The Unwin/Bakhurina influence is wide ranging
Elgin, Hone and Frey (2011) bought into the Unwin/Bakhurina hypothesis. Earlier and here we were able to dismiss the evidence they presented, which included the untenable concept of “tissue shrinkage” to explain away the obvious situation in Pterodactylus. Palmar and Dyke (2011) also adopted a deep chord wing membrane and uropatagium model. Earlier and here we were able to dismiss the evidence they presented. Kellner et al. (2010) likewise followed suite and that evidence was dismissed here.

Sometimes you just have to raise your hand when something doesn’t make sense and for which there is no evidence. The power of the paradigm and the professor is mighty.

Decoupling
Because the wing membranes become narrow at the elbow and the uropatagia are split, pterosaur wings are decoupled from their legs and they are freed from the imaginary shackles put upon them by well-meaning but misguided pterosaur experts who continue to disfigure our favorite pterosaurs, also discussed more recently here in a discussion of an IMAX feature film starring David Attenborough.

Doggone it,
we need a Pterosaur Renaissance to pull us out of the quagmire created by these tail-dragging experts.

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
Bakhurina NN and Unwin DM 2004. Reconstructing the flight apparatus of Eudimorphodon. Rivista Museo civico di Scienze Naturali “Enrico Caffi” Bergamo 22 2003:5-8.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeonntologica Polonica 56(1): 99-111.
Kellner AWA, Wang X, Tischlinger H, Campos DA, Hone DWE and Meng X 2010. The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane. Proc Royal Soc B 277: 321–329.
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.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95–120.

wiki/Sordes
wiki/Eudimorphodon

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