A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings
The wings of birds and their closest theropod relatives share a uniform fundamental architecture, with pinnate flight feathers as the key component1, 2, 3. Here we report a new scansoriopterygid theropod, Yi qi gen. et sp. nov., based on a new specimen from the Middle–Upper Jurassic period Tiaojishan Formation of Hebei Province, China4. Yi is nested phylogenetically among winged theropods but has large stiff filamentous feathers of an unusual type on both the forelimb and hindlimb. However, the filamentous feathers of Yi resemble pinnate feathers in bearing morphologically diverse melanosomes5. Most surprisingly, Yi has a long rod-like bone extending from each wrist, and patches of membranous tissue preserved between the rod-like bones and the manual digits. Analogous features are unknown in any dinosaur but occur in various flying and gliding tetrapods6, 7, 8, 9, 10, suggesting the intriguing possibility that Yi had membranous aerodynamic surfaces totally different from the archetypal feathered wings of birds and their closest relatives. Documentation of the unique forelimbs of Yi greatly increases the morphological disparity known to exist among dinosaurs, and highlights the extraordinary breadth and richness of the evolutionary experimentation that took place close to the origin of birds.Supplementary information:
If a membrane is reconstructed lateral to the trunk, the wing is similar in outline to ........ a pterosaur wing if the styliform element is approximately laterally oriented.Extended data:
If the Xu et al interpretation is correct, then Yi qi is the perfect candidate for transitional between pterosaur and paraves.
Here are a few other references:
These wings were mutually exclusive: dinosaur or pterosaur, feathery or leathery. But Yi went for both options! It had membrane wings with a feathery covering on the leading edge. It shows that at least some dinosaurs had independently evolved the same kind of wings as pterosaurs—an extraordinary example of convergent evolution.
It is here that we enter unicorn territory — for no dinosaur, however unusual, has been found with anything like this feature. The authors are appropriately cautious, therefore, in their interpretation.http://www.theguardian.com/science/lost-worlds/2015/apr/29/bird-yi-qi-the-dinosaur-evolution-flight-feather-nature
A dinosaur called Yi qi appears to have lifted a page from pterosaurs’ flight plan. Protruding from each of the newly discovered dinosaur’s wrists was a weird rodlike bone that may have attached to a fleshy wing that helped the dinosaur glide or fly, researchers report April 29 in Nature.“We’ve never seen anything like this in a dinosaur before,” says paleontologist Sarah Werning of Stony Brook University in New York. “It’s almost like this dinosaur was pretending to be a pterosaur.”
Xu et al "identify the three manual digits of Yi and other maniraptors as II-III-IV".
The Pterosaur Model (not shown) differs from the Bat Model in having
a laterally oriented styliform element (which is redundant functionally with the elongated manual digit IV), but otherwise is nearly identical to the Bat Model.
A key weakness of the Bat and Pterosaur Models is that no membranous soft tissue is preserved lateral to the body and posterior to the humerus and ulna in the holotype of Yi qi, whereas relatively large feathers are clearly present in this region. The feathers may simply have been situated ventrally and/or dorsally on the membrane, for purposes of insulation and/or display, but their large size implies that they might then have increased the drag experienced by the animal to strongly disadvantageous levels.
The major strength of the Bat and Pterosaur Models is that the reconstructed wing has a large membranous area and represents a general type of aerodynamic apparatus that is common among volant tetrapods other than birds and their close relatives 14-19,22Kevin Padian commentary: