The carpus (wrist) of Pterodactylus scolopaciceps

Earlier we looked at the pectoral girdle of Pterodactylus scolopaciceps  BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991).. And even earlier we looked at that elusive (they say it doesn’t exist!) manual digit 5. Today, some more thoughts on that wonderful wrist… (Fig. 1).

Figure 1. The wrist of Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991). Manual digit 5 is a vestige, but it is there.

Figure 1. The wrist of Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991). Manual digit 5 is a vestige, but it is there.

Manual digit 5
is here. So is metacarpal 5 and distal carpal 5

Figure 1. The wrist of Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991). Manual digit 5 is a vestige, but it is there.

Figure 2. The wrist of Pterodactylus scolopaciceps BSP 1937 I 18 (Broili 1938, P. kochi n21 of Wellnhofer 1970, 1991). Manual digit 5 is a vestige, but it is there.

Metacarpals 1-3
are not pasted onto the anterior (during flight) face of the big metacarpal 4 as tradition dictates. Here mc1-3 are in their natural positions for tetrapods, palmar side down. Only metacarpal 4 is axially rotated so the wing finger folds (flexes) and extends in the place of the hand like bird and bat wings do. That means only metacarpal 3 attaches to metacarpal 4, mc2 lies between 1 and 3 and 1 hangs out in front.

Fingers 1-3
are dislocated and axially rotated anteriorly. In life they palms of the fingers would have been ventral, just like metacarpals 1-3 — not flexing anteriorly as they do here after crushing. Note the fingers are all disarticulated at the knuckle, which was a very loose joint, enabling 90 degrees of extension dorsally (in flight) or laterally (while quadrupedal for walking. Moreover, digit 3 was able to flex in the plane of the wing, like the wing. That produces manus impressions in which digit 3 is oriented posteriorly. That’s very weird for most tetrapods, but common in pterosaurs, as it indicates the quadrupedal configuration was achieved secondarily from an initial bipedal configuration.

Of added interest here….
Note the sawtooth posterior edges of the forelimb, hand and finger four where the wing membrane was attached, fed and enervated. Note also the large extensor tendon distal to the preaxial carpal. It is rarely preserved.

The preaxial carpal and pteroid
as you might remember, are former centralia having migrated to the outside (Peters 2009). We looked at analogous migrations here.

Radius and ulna
as in birds and bats, there is no pronation or supination in the pterosaur wrist and forearm. The elements are too close together to permit this. And that’s a good thing to keep the wing in the best orientation for flight. Bats and birds don’t twist their forearms either.

As you already know, every body part that disappears
goes out with a vestige.

References
Broili F 1938. Beobachtungen an Pterodactylus. Sitz-Bayerischen Akademie der Wissenschaten, zu München, Mathematischen-naturalischenAbteilung: 139–154.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.

wiki/Pterodactylus

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