Variation in Three Sordes Specimens

Uropatagium of Sordes according to Sharov 1971 and Unwin/Bakhurina 1994.

Figure A. Uropatagium of Sordes according to Sharov 1971 and Unwin/Bakhurina 1994.

Despite it’s fame and antiquity
(some 40 years after discovery) very little has been published on the first hairy pterosaur, Sordes pilosus (Sharov 1971). We’ve seen photos of three (Figs. 2, 4, 6) of the eight or nine reported specimens and Sharov’s original illustration of the holotype (Fig. A). Then there’s my own published tracing (Peters 2002) based on photos of the holotype (PIN 2585/3, Fig. 2). Other workers (Elgin et al. 2011, Unwin and Bakhurina 1994, Wellnhofer 1991) have simply lifted or retraced Sharov’s tracing of the bones and membranes, which are a little cartoony at best.

Three years ago,
for the Sordes webpage of reptileevolution.com I took the easy road out and created a chimaera, adding the head of 2585/25 (Figs. 3, 4) to the headless holotype 2585/3 (Figs. 1, 2). That’s not a good practice. In doing so one assumes that each of the contributing specimens is conspecific. That’s almost never true in pterosaurs as work with Rhamphorhynchus, Dorygnathus, Germanodactylus, Pteranodon, and Pterodactylus has already demonstrated.

Today we’ll reconstruct the three specimens (PIN 2585/3, PIN 2585/25 and a third unidentified specimen) that have been published as photos to compare and contrast them.

Figure 1. Sordes holotype 2785/3. The skull is perhaps present, but so degraded it must be considered unknown.

Figure 1. Sordes holotype PIN 2585/3. The skull is perhaps present, but so degraded it must be considered unknown. Here it is grayed out to show it is poorly known and the skull reconstruction makes it a chimaera.

The holotype PIN 2585/3 (Figure 1). is complete, but lacking a skull.

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

Figure 2. Sordes holotype, PIN 2585/3. Soft tissue in abundance, but the skull is largely gone. Click to see where the displaced radius and ulna are.

The PIN 2585/3 holotype is the only Sordes specimen for which bones were identified, which is key to specimens that preserve so much camouflaging soft tissue. The displaced arm bones that dragged the wing membrane back to the hind limbs are shown here.

Figure 2. The PIN 2585/25 specimen of Sordes. This is the specimen that shows the skull in lateral view.

Figure 3. The PIN 2585/25 specimen of Sordes. This is the specimen that shows the skull in lateral view. Scale unknown.

The second specimen PIN 2585/25 also has a short torso, in this case subequal to the skull. No soft tissue here, but a great view of the skull in lateral view.

Figure 4. Sordes specimen PIN2585/25. No soft tissue here.

Figure 4. Sordes specimen PIN2585/25. No soft tissue here.

The third specimen (no number known so far) has lots of hair, but preserves the skull in ventral view. You can still see the buried side from the inside through the mandibles,  so you can still get close on skull reconstruction.

Figure 3. PIN specimen number unknown. Scale unknown. This is the specimen that shows the  mandible in ventral view with a fish alongside.

Figure 5. PIN specimen number unknown. Scale unknown. This is the specimen that shows the mandible in ventral view with a fish alongside.

The third specimen has a longer torso, longer than the skull. The shape of the humerus is different. The wing is relatively short. The teeth are smaller. So is the antorbital fenestra.

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

Figure 6. The third Sordes specimen PIN number unknown. That is a small fish in the middle. Lots of soft tissue here.

The third specimen (Fig. 6) includes a fish alongside and lots of hair. The radius and ulna are largely buried beneath the dorsal vertebrae with only the ends exposed.

Figure 8. The three Sordes specimens. Scale for right specimen only. Others scaled to matching skull lengths.

Figure 7. The three Sordes specimens. Scale for right specimen only. Others scaled to matching skull lengths. Missing tails here are missing in the fossils. The humerus is different in each specimen.

Putting all the Sordes specimens together (Fig. 7, sorry no scale here as scale bars are unknown for two of the specimens). This form of presentation makes it easier to see the differences and similarities.

Phylogenetic analysis nests all three Sordes specimens very close to the basalmost Dorygnathus, the Donau specimen (Fig. 9). Actually, for one of them, a little too close.

Figure 8. The Donau specimen of Dorygnathus is very close to Sordes.

Figure 8. The Donau specimen of Dorygnathus is very close to Sordes.

Like the tall third specimen of Sordes, Dorygnathus has a longer torso, but not a larger sternal complex, which remains a small triangle. So, the small sternal complex that characterizes Dorygnathus (easy to distinguish from broad-chested Rhamphorhynchus), originated with Sordes.

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 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

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