18 février 2017

Sharovipteryx


Un reptile qui avait des ailes sur ses pattes... postérieures? Incroyable! C'est pourtant vrai:

Sharovipteryx, from the Mid Triassic of Kyrgyzstan had the oddest "wings" of any fossil reptile, stuck to its hind limbs. This unique delta-winged creature glided effortlessly between the trees of its forest home. It was a design that would never again reappear in nature.

(...) The animal is known from only one specimen, or the holotype, the specimen upon which the species description is based. It is an articulated skeleton, quite complete and well-preserved so it is somewhat easy to produce a confident bodily reconstruction of the creature.

This fossil shows a 25-centimeter animal, very thin and narrowly built with a small, 1.9-centimeter skull. The teeth were spaced widely apart in the animal's jaws. It had wide, five-toed feet and lengthy legs in proportion to its body. Skin impressions from the holotype show it was covered in overlapping, lizard-like scales. The characteristic hind leg "wing" membrane is made of skin, with no scale cover.  

(...) Sharovipteryx's "wing" membrane must have been unique not because it was such a one-off but because of the anatomy of the creature itself and the time during which it lived. According to Mark Witton, it is not that the gliding mechanism was inefficient. Instead, to develop this wing configuration, he believes that the animal's ancestors had to start out as climbers with enormously elongated back legs that splayed out to the sides. From here it was just a matter of leaping from tree to tree, just like any other gliding arboreal animal, either living or extinct. That is, an animal with the same configuration as Sharovipteryx, or possibly a relative or ancestor.

A long-legged biped without this kind of leg rotation could never develop this system. The protorosaurs themselves never made it past the Triassic, hence the end of this odd gliding system. According to Witton, the long-legged Sharovipteryx was not just an evolutionary oddball but also a member of an evolutionary line that would prove to be unlucky.



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