The Hands of Sharovipteryx

The hands of Sharovipteryx have been considered “missing” since Sharov (1971) did not illustrate them, other than finger 4 of the left hand.

Sharov's illustration of finger 4.

Figure 1. Sharov’s illustration of finger 4.

I Blame It on Soft Tissue
Sharovipteryx preserves soft tissue from it s scaly snout to its webbed toes. Soft tissue also obscured the hands on the counterplate. Here (Fig. 2) I traced what faint impressions remained of the fingers using DGS (digital graphic segregation). Yes, it’s difficult to discern. Whether illusions or not, both hands matched each other and their ratios and patterns matched or were transitional between those of sister taxa, Cosesaurus and Longisquama.

The pectoral girdle and forelimbs of Sharovipteryx.

Figure 2. The pectoral girdle and forelimbs of Sharovipteryx. Both sides match each other and fit neatly into their phylogenetic node between sisters Cosesaurus and Longisquama.

Reconstruction
The reconstructed hand of Sharovipteryx (Fig. 3) had the appearance of a stunted limb, with a reduced yet robust humerus and radius+ulna. Certainly neither supination nor pronation was possible. A pteroid was retained. Unlike the other basal fenestrasaurs, all four metacarpals were subequal in length. Metacarpal 4 was more robust than the others and its terminal articular surface was expanded, as in pterosaurs. Digit 4 was also more  robust, especially proximally, as in pterosaurs. The claws were sharp, but not especially trenchant. The PILs (parallel interphalangeal lines) were continuous across all four digits indicating that all the phalanges flexed as phalangeal sets, as in other tetrapods, other than Longisquama and pterosaurs.

The reconstructed hand of Sharovipteryx.

Figure 3. The reconstructed hand of Sharovipteryx. The proximal elements were reduced. Despite the appearance here of a rotated metacarpal 4, the PILs remained continuous indicating that digit 4 probably had not rotated (as in pterosaurs and Longisquama), but remained a part of the flexion set. Even so metacarpal 4 was enlarged relative to the others, so the wing-making process had begun. 

Evolutionary Significance
Even though Sharovipteryx is the sole representative of a distinct fenestrasaur branch in which the hind limbs were emphasized, the forelimbs were de-emphasized and the neck was elongated, it still demonstrated traits illustrating the evolution of pterosaurian traits beyond those of Cosesaurus, but not  to the level of Longisquama.

Usefulness?
Were the hands of Sharovipteryx useless vestiges? Or were they important canards used aerodynamically to affect pitch control? The hands of Sharovipteryx were likely trailed by soft tissue membranes, since both taxa in its phylogenetic bracket (Cosesaurus and Longisquama) had such membranes. With a robust stem-like coracoid, Sharovipteryx was able to flap its arms, providing only a small amount of thrust. Thrust vectoring would have been most useful to raise the front of the body during a landing in order to stall the large hind-leg wing and execute a gentle two-point landing. It is hard to imagine the small hands of Sharovipteryx used to cling to tree trunks, but perhaps they did so if Sharovipteryx bellied up to a big one.

 

Figure 2. Sharovipteryx mirabilis in various views. No pycnofibers added yet. Click to learn more.

Figure 4. Sharovipteryx mirabilis in various views. Trailing membrane on the hand is guesswork based on phylogenetic bracketing. Click to learn more.

Was Metacarpal 4 Rotated?
Good question. Hard to tell. Some evidence points one way. Other evidence does not. Perhaps this stage is the transition one. That makes sense for several reasons.

We’ll look at the skull next…

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
Dyke GJ, Nudds RL and Rayner JMV 2006. 
Flight of Sharovipteryx mirabilis: the world’s first delta-winged glider. Journal of Evolutionary Biology.
Gans C, Darevski I and Tatarinov LP 1987. Sharovipteryx, a reptilian glider?Paleobiology, October 1987, v. 13, p. 415-426.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
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].

wiki/Sharovipteryx

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