Longisquama wings

Everyone agrees
that the anterior half of Longisquama is known because it is plainly visible. Everyone agrees that a pair of forelimbs is visible. Sharov (1970) illustrated fingers, but was stymied from completing that task because the two hands are preserved one on top of the other with the fingers intermingled. You can see that chaotic preservation here.

DGS
(digital graphic segregation) is a useful method to segregate one Longisquama hand from another and fingers from one another. Once that is done, phalangeal lengths can be matched for validity and accuracy. Ultimately a reconstruction can be produced (Fig. 1). It is readily apparent that the in situ chaos as preserved is difficult to trace, but not impossible. Anyone can do it with enough resolution and patience.

Figure 1. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized, as in pterosaurs.

Figure 1. Longisquama left and right manus traced using DGS then reconstructed (below). This is a very large hand for a fenestrasaur and manual digit 4 is oversized, as in pterosaurs. Yes, membranes are preserved trailing the manus, just as plumes and other membranes are preserved elsewhere.

The importance of overcoming a chaotic preservation
to retrieve an orderly reconstruction is well illustrated by this example (Fig. 1). The fact that corresponding phalanges on both hands are equal in length self-validates the tracing. Here the phalanges are numbered and their images were copied and pasted to produce the reconstruction. Also note the shapes of the scapula and coracoid, perfect for flapping. There’s a nice sternal complex in there too. Only fenestrasaurs, including pterosaurs, have those.

The size of the manus,
relative to the humerus and antebrachium, the proportions of the phalanges, the presence of a trailing membrane and of preaxial carpals (including a pteroid) all indicate a close relationship to pterosaurs and other fenestrasaurs. No other tetrapods share these traits.

Figure 2. Click to animate. Longisquama flapping and wagging its tail.

Figure 2. Click to animate. Longisquama flapping and wagging its tail.

Scientists have been looking
for a non-flying reptile with large hands that could be a pterosaur ancestor. This is it (fig. 2), only the fingers are a little curled up and relative to the torso the entire forelimb is short, as in the sister to Longisquama, Sharovipteryx.

References
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 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

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