Sharovipteryx miribilis (Sharov 1971) Norian, Late Triassic, ~210 mya was originally considered a pseudosuchian, then a prolacertiform (Peters 2000). Here it nests as a lizard derived from a sister to Cosesaurus. Sharovipteryx is a sister to Longisquama and pterosaurs.
Distinct from Cosesaurus, the skull of Sharovipteryx had an upturned premaxilla with procumbent teeth. The naris was enlarged and a single smaller antorbital fenestra was present. The postorbital was higher relative to the orbit. The rostrum was straighter. The ventral mandible was more convex. The teeth were more varied in shape, with rear teeth having several cusps for cracking insects. Long hyoids emerged from the base of the throat.
The cervicals were hyper-elongated. The dorsals were shortened. Several dorsals joined the sacral series in response to the increase in stress of the bipedal configuration. The caudals were lengthened. The dorsal ribs extended horizontally creating a wide but shallow torso.
The coracoid was straighter. The entire forelimb was reduced. The humerus was robust with a large deltopectoral crest. The ulna and radius were also robust, but shorter than the metacarpus. Digit IV was discovered by Sharov (1971) extending back to the pelvis. The other digits, long considered missing, are identified below.
The ilium was hyper-elongated, both anteriorly and posteriorly. The puboischium was deeper than in Cosesaurus. The prepubis was straighter. The hind limbs were extremely long with a femur longer than the torso. The distal femur had a short anterior extension to prevent overextension of the tibia. The metatarsals spread apart, unlike other fenestrasaurs. Digit V was further elongated.
Various extradermal membranes surrounded Sharovipteryx. The neck skin was 6x wider than the cervicals and able to be spread even wider by extension of the hyoids. Fiber-supported uropatagia extended from the hind limbs, from digit V to the base of the tail. Smaller membranes extended anterior to the femur and at the base of the tibia. Webbing was between the toes. Elongated fibers tipped the tail. Fiber-embedded membranes were also preserved in the damaged areas around the forelimbs. See below.
With its diminutive forelimbs, Sharovipteryx would seem to be dissimilar to pterosaurs, but the rest of its traits find no better match. With such long hind limbs, Sharovipteryx was unable to walk quadrupedally, but leaping between trees was greatly improved. It is widely held that pterosaurs were ALL quadrupedal, but Cosesaurus and Sharovipteryx were facultative and obligate bipeds respectively. Even Scleromochlus, the preferred pterosaur sister taxon of Bennett (1996), Senter (2003) and Hone and Benton (2008), was a biped, so it is strange that Hone and Benton (2007) objected when Peters (2000) presented fenestrasaurs as bipeds. |
