The Skull of Sharovipteryx

Apart from the hands of Sharovipteryx, the skull (Fig. 1) has given workers (including yours truly) much trouble. Although complete and largely articulated, the skull was crushed and invaded by a wasp-like, ant-like insect. My mistake (Peters 2000) was considering the large split posterior bones to be between the pterygoids, which they resemble. However, when reassembled in three-dimensions, the split disappears as the dome-like frontals and parietals come together at the midline. Not all the bones are bone-colored. Some remain wrapped in scaly skin.

DGS
I used DGS (digital graphic segregation) to identify the bones. If someone else wants to re-identify the skull bones of Sharovipteryx, please report any and all confirmations and discrepancies.

sharovipteryx-skull588

Figure 1. The skull of Sharovipteryx in situ (right) and traced left). Note the details visible in the scalation of the snout and the wrinkles (or are those pycnofibers?) of the neck, along with the breadth of the neck skin relative to the narrow cervicals. This image supersedes an earlier one.

Reconstructed Skull
Copying and pasting the skull elements recovers a skull midway between those of Cosesaurus and Longisquama + basal pterosaurs (Fig. 2). The naris was enlarged and largely posterior to the tooth-bearing portion of the premaxilla. The ascending process of the premaxilla extended to the anterior orbit. The maxilla included two longer teeth ventral to the ascending process while some of the posterior teeth were multi-cusped. The narrow snout and wide cranium afforded some degree of binocular vision. The orbit was the largest skull opening, twice the size of the antorbital fenestra (without a fossa). The naris was also larger slightly than the antorbital fenestra. The skull was domed. The dorsal rim of the postorbital was in line with the orbit dorsal rim. The palate was relatively gracile with a robust anterior pterygoid. The palatine and ectopterygoid were in contact with one another, prior to their fusion in pterosaurs to form the L-shaped ectopalatine. The dentary included procumbent anterior fangs and posterior multi-cusped teeth.

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

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

Phylogenetic Results
Despite its unique body, the reconstructed skull of Sharovipteryx offers few surprises or unexpected adornments. It appears to be a standard primitive fenestrasaur skull, a little longer than in Cosesaurus with teeth more like those of basal pterosaurs and Longisquama.

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
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
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

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

The Aerodynamics of Sharovipteryx – the Hind Wing Glider

It’s obvious that Sharovipteryx was built to be a glider. But it’s the elongated, stick-like hind legs – rather than the barely visible fore legs – that acted like wings – and that’s enough to throw most of us for a loop. What gives here?? Everyone imagined a lack of pitch control in such a creature.

To counter this pitch problem, Sharov (1971, Fig. 1) invented a membrane stretching from the back of the largely imagined arms to the front of the legs in a rather cartoonish presentation.

Various reconstructions of Sharovipteryx

Figure 1. Various reconstructions of Sharovipteryx

Gans et al. (1987) observed no membrane between the front and hind legs. Even so, experiments with paper models (Fig. 1) showed that a canard membrane would have stabilized the animal in the air and extended its glide.

Wellnhofer (1991) simply re-illustrated what had been previously published, likewise imagining front limbs supporting a canard, but not connected to the hind limbs.

Dyke et al. (2006) could find no membranes anterior to the hind legs, but imagined some that created a delta wing like certain aircraft. These authors also imagined a small delta canard wing anterior to the forelimbs for pitch control.

As you can see, there has been no loss of imagination in trying to figure out the extent of the wing membranes in Sharovipteryx. Unfortunately, there has been an embarrassing lack of attention to detail.

Figure 2. The wing membranes of Sharovipteryx.

Figure 2. The wing membranes of Sharovipteryx.

The Search for Anterior Control Membranes
While others searched in vain for anterior membranes capable of controlling pitch in Sharovipteryx, I found them (Fig. 2), either by direct observation or phylogenetic bracketing.

Neck Strakes
Two large hyoids (tongue bones) could have spread that loose preserved neck skin up to 6x their original width (3x per side, in pink, Fig. 2). This action would have created aerodynamic strakes, also found in modern jets like the F-18. Lifting and depressing the head, via the neck, would have elevated and depressed the strake, giving Sharovipteryx great pitch control.

Forelimb Canards
Both forelimbs are preserved virtually in their entirety.  When recontructed they look stunted, but they were robust with traits also found in Longisquama and Cosesaurus like an expanded distal end and a large deltopectoral crest and parallel, appressed ulna and radius. These traits also include a tiny pteroid and preaxial carpal (Fig. 2.), bones traditionally found only in pterosaurs, but also found in Cosesaurus (Peters 2009). Digit 4 was the longest (reaching to the pelvis in Sharov’s (1971) original illustration). Digit 5 was a vestige. Since sister taxa, Cosesaurus and Longsiquama had trailing edge membranes, phylogenetic bracketing permits us to add them to Sharovipteryx (Fig. 2). These would have acted like canards, small forewings capable of independent movement, but most typically extended straight out, supported by a robust scapula and coracoid. The sternal complex remains buried in Sharovipteryx, but phylogenetic bracketing indicates it had this fenestrasaur trait as well.

Pancake-like Ribs
A trait that has gone overlooked in prior reconstructions (Fig. 1) is how broad and flat the rib cage was. In dorsal view it formed a circular disc. This shape filled the area between the fore and hind limbs without the invention of a connecting membrane.

Small Anterior Leg Membranes
A small stiff membrane anterior to the femur helped fill the gap otherwise present when the straight femur met the circular dorsal ribs. Another small stiff membrane appeared at the distal tibia.

Interdigital Membranes
Between the toes membranes extended only as far as the proximal interphalangeal joints medially, further laterally, extending to ungual 4 lateral to digit 4.

Uropatagia
Aft of the hind legs, the patagia are well represented in the fossil. These fiber-embeded membranes extended to the second joint of digit 5 and to the second chevron on the tail.

Long, Flat Thighs
The elongated ilia, both fore and aft, would have supported wide thighs, at least proximally.

Summary
Far from lacking anterior pitch-control membranes, Sharovipteryx had both strakes and canards. Since the coracoids were elongated and stem-like, Sharovipteryx probably flapped its small forelimbs, generating a small amount of thrust. Primarily Sharovipteryx was a glider, and a well-controlled one! This obvious obligatory biped had to have been agile enough to land using its feet alone, as in birds. When approaching a landing spot, the anterior control surfaces would have been raised to stall the main flight membrane just prior to touch down.

More on Sharovipteryx in the next two blogs: the hands and the skull.

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].
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander, London

wiki/Sharovipteryx