Sharovipteryx

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Sharovipteryx
Fossil range: Early Triassic

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Infraclass:	Archosauromorpha
Order:	Prolacertiformes
Family:	Sharovipterygidae Tatarinov, 1989
Genus:	Sharovipteryx

Binomial name

Sharovipteryx mirabilis
(Sharov, 1971)

Synonyms

Podopteryx mirabilis Sharov, 1971

Sharovipteryx ("Sharov's wing", previously known as Podopteryx, "foot wing"), was among the earliest gliding reptiles, from the early Triassic period. It was approximately eight inches long, with an extremely long tail, and weighed about 7.5 grams. It may have been related — or perhaps even ancestral — to pterosaurs,^[1] although this remains controversial. Unlike pterosaurs, its main flight membrane was stretched between long back legs rather than its very short front limbs.

Sharovipteryx mirabilis.

Alternate skeletal interpretation by David Peters.

If Sharovipteryx was a relative of pterosaurs, then its membrane may have stretched to its front legs, or it may have had a separate membrane joined to its front limbs alone. Although front wing membranes have not been seen, the fingers have been traced by Peters^[2] and they show similarities to Cosesaurus and Longisquama and to a lesser extent, pterosaurs. Some scenarios have it as a leaping animal, which would spring up in the air and then control its fall with its "wings". This fits well with the belief that pterosaurs evolved from running, leaping ancestors, because some scientists believe they lacked adaptations for living in trees. However, others suggest that Sharovipteryx would run up a tree on its sharply clawed rear legs (its overall design seems poor for climbing), and then spring into the air. The forelimbs seem too short for quadrupedal running or climbing. Such a configuration was probably necessary in order to free the forelimbs from the task of walking and allow them to become something else.

Sharovipteryx was a biped in the manner of living lizards capable of bipedal running, except that Sharovipteryx had a better pelvis, more sacaral vertebrae, longer hind limbs, a shorter torso and a thinner tail than any living lizard. The dimunition of the tail muscles and the increase in the pelvic muscles shows that Sharovipteryx was on its way toward a pterosaur-like metabolism, probably homeothermic. It was not depending on torso undulations for locomotion and therefore not subject to Carrier's Restraint on breathing while running.

Scharovipteryx as delta-wing glider

In 2006, Dyke et al.^[3] published a study on possible gliding techniques for Sharovipteryx. The authors found that the wing membrane, which stretched between its very long hind legs and tail, would have allowed it to glide in a manner similar to delta wing aircraft. If the tiny front limbs also supported a membrane, they could have acted as a very efficient means of controlling pitch stability, very much like a canard. Without a forewing, the authors find, controlled gliding would have been very difficult (unfortunately, the area around the forelimbs was completely prepared away in the only known fossil, destroying any possible trace of a membrane there). Another membrane, the wrinkled skin of the neck, is preserved 6 times wider than the slender cervical vertebrae. Slender and long ceratobranchial bones invade the neck from the throat. If the ceratobranchials spread laterally, as they do in some living lizards, then the wrinkled neck skin could expand laterally, forming aerodynamic strakes, as found on modern fighter jets. Together with the canards on the forelimbs, these anterior membranes may have formed excellent control surfaces for gliding.

Sharov in 1971^[4] illustrated the finger tips to the elongated digit IV in both hands. Another study by Peters in 2006 found all the fingers of both hands, and argued that if canard wings were present, they were not as imagined by the Dyke study, which did not observe the fingers.

[edit] 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. (2006). "The Front Half of Sharovipteryx" Prehistoric Times 76: 10-11.
^ Dyke, G.J., Nudds, R.L. and Rayner, J.M.V. (2006). "Flight of Sharovipteryx mirabilis: the world's first delta-winged glider." Journal of Evolutionary Biology.
^ Sharov, A.G. 1971. New flying reptiles fro the Mesozoic of Kazakhstan and Kirghizia. - Trudy of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].