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How one Sordes evolved into Dorygnathus via Cacibupteryx

Monday, March 9, 2015 10:35

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I have seen images of three
more or less complete Sordes (Sharov 1971, Oxfordian/Kimmeridgian) specimens (Figs. 1-3). Unfortunately only the holotype PIN 2585/3 (Fig.1) was described (Sharov 1971). Later Unwin and Bakhurina (1994) echoed Sharov’s findings, that Sordes had wing membranes attached to the legs and another membrane (uropatagium) between the legs, but their tracings were, at best, outlines. No one else who has actually seen this taxon has further described the holotype in more detail with precise tracings. And it’s been almost 45 years!

Figure 2. Sordes holotype, PIN 2585/3. Soft tissue in abundance, but the skull is largely gone.

Figure 1. Sordes holotype, PIN 2585/3. Soft tissue in abundance, but the skull is largely gone.

The Sordes paratype PIN 2470/1 (Fig. 2) includes a fish and lots of hair. (Unwin 2006 reports that nine specimens of Sordes were found in the 1960s), all undescribed at present.

Figure 4. The third Sordes specimen PIN number unknown. That is a small fish in the middle. Lots of soft tissue here.

Figure 2. The paratype of Sordes specimen PIN 2470/1). That is a small fish in the middle. Lots of soft tissue here.

A third specimen
of Sordes (PIN 2585-25) is also well known and shows the skull in lateral view. Soft tissue is present here, but much less extensive. Even less well known are the five or six other specimens (among them: PIN 104/73, PIN 2585/36, PIN 2585/37) Are they just bits and pieces? Does anyone know? Are they published anywhere? I have a note into the PIN for more info, but so far no reply.

Figure 2. The PIN 2585-25 specimen of Sordes.

Figure 3. A third specimen of Sordes, PIN 2585-25.

The three specimens have all been identified as Sordes, but they nest in three distinct nodes on the large pterosaur tree, phylogenetically closer to other taxa than to each other (Fig. 4).

Figure 4. The three Sordes specimens to scale. They are close, but not identical. Shown above each is a closer sister taxon. Click to enlarge.

The Cacibupteryx connection
Cacibupteryx caribensisi (Gasparini, Fernández, and de la Fuente, 2004) Oxfordian, Late Jurassic ~160 mya was considered a rhamphorhychid and a scaphognathid, but it nests as a very basal dorygnathid. Derived from a sister to Sordes, Cacibupteryx phylogenetically preceded all specimens of Dorygnathus.

Figure 4. Cacibupteryx to scale with the 2585/36 specimen attributed to Sordes. These two nest together in the large pterosaur tree.

Figure 5. Cacibupteryx ( IGO-V 208) to scale with the 2585/36 specimen attributed to Sordes. These two nest together in the large pterosaur tree, not quite with Sordes. These two were contemporaries, both from the Tropic of Capricorn, not a world apart, as they are now, but part of the supercontinent Pangaea prior to the appearance of the North Atlantic.

The Jianchangopterus connection
The holotype of Sordes (Fig. 4) nests with Jianchangopterus, at the the base of Pterorhynchus + the Wukongopteridae not far from the base of Scaphognathus and its many descendants. So with one Sordes at the base of all dorygnathids and one Sordes near the base of all scaphognathids, that means Sordes is the last common ancestor of all pterodactyloid-grade pterosaurs in the large pterosaur tree — still pretty far from any pterodactyloid-grade pterosaurs, which had four separate origins.

One wonders
why the other six specimens of Sordes have not been released. Are they just scraps? It’s been fifty years since their discovery. It’s time those specimens were presented and all three Sordes specimens were reintroduced in an academic publication. Since the three well-preserved specimens attributed to Sordes nest close to one another, but are not conspecific or even congeneric on the cladogram. doubt may be cast on the identity of the remaining specimens. We’ll have to see…

References
Cheng X, Wang X-L, Jiang S-X and Kellner AWA 2012. A new scaphognathid pterosaur from western Liaoning, China. Historical Biology iFirst article available online 29 Nov 2011, 1-11. doi:10.1080/08912963.2011.635423
Gasparini, Z, Fernández M and de la Fuente M 2004. A new pterosaur from the Jurassic of Cuba. Palaeontology 47(4): 919–927. doi:10.1111/j.0031-0239.2004.00399
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.
Zhou C-F 2014. Cranial morphology of a Scaphognathus-like pterosaur, Jianchangnathus robustus, based on a new fossil from the Tiaojishan Formation of western Liaoning, China. Journal of Vertebrate Paleontology 34(3):597-605.