Most pterosaur fossils are incomplete, crushed and disarticulated. By contrast, Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991, Fig. 1) is just the opposite, complete, uncrushed and articulated. (This specimen is commonly considered P. kochi, but the holotype of P. kochi lies outside the Pterodactylus clade and is also basal to the Germanodactylus clade.)
Figure 1. Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi No. 21 of Wellnhofer 1970, 1991) complete, articulated and including soft tissue.
That elusive and some would say mythical manual digit 5
So, if pterosaurs had five manual digits, as shown on many other specimens, this specimen should show them complete, uncrushed and articulated.
And it does! Can you see them (Fig. 2)?
Figure 2. Metacarpi of n21. Can you see the vestiges of digit 5 on these images? If not, see figure 3. Note the position of the preaxial carpal, leaning distally while flexed. Extension of the elbow would pull this bone medially by way of extensor tendons.
If you can’t see the vestiges of manual digit 5, please see the next image (Fig. 3) in which the elements are colorized. The posterodorsal position of this digit documents the axial rotation of metacarpal 4, which enables the pterosaur wing to fold in the plane of the wing. This disproves Bennett’s (2008) ghastly hypothesis that the forelimb pronated then finger 4 hyperhyperhyperextended to enable folding against the posterior (former dorsal) side of the hand. Ouch!!
Figure 3. Colorized digit 5 elements including ungual, two other phalanges, metacarpal and carpal 5. Manual digit 5 is present on both metacarpals. All the elements match one another. On the lower image (the right one) digit 5 (or at least the ungual) is rotated axially about 180 degrees, perhaps due to disarticulation.
And here’s a closeup. Note the presence of carpal 5 (pink), metacarpal 5 (green), and three phalanges including the ungual, as in Cosesaurus and other tritosaurs.
Even in primitive snakes some sort of vestige of hind limbs is preserved. So, while digit 5 was shrinking from Cosesaurus to pterosaurs, it remained a vestige in many, if not all pterosaurs, just sitting there, like a human appendix.
Figure 4. Pterodactylus manual digit 5 vestige. Sorry for the over enlargement. Someday someone should take a sharper image of this.
Tomorrow we’ll take another look at n21, a perfect Pterodactylus and find the wingtip unguals.
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
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Broili F 1938. Beobachtungen an Pterodactylus. Sitz-Bayerischen Akademie der Wissenschaten, zu München, Mathematischen-naturalischenAbteilung: 139–154.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
The Pterosaur Heresies 