'wing' and 奇; qí; 'strange'), is known from a single fossil specimen of an adult individual found in Middle or Late Jurassic Tiaojishan Formation of Hebei, China, approximately 159 million years ago.

Like other scansoriopterygids, Yi possessed an unusual, elongated third finger, that appears to have helped to support a membranous gliding plane made of skin.

This modified wrist bone and membrane-based plane is unique among all known dinosaurs, and might have resulted in wings similar in appearance to those of bats.

The first and only known fossil specimen of Yi qi was found by a farmer, Wang Jianrong, in a quarry near Mutoudeng Village (Qinglong County, Hebei).

The team of scientists who authored this initial study were led by Xu Xing and also included Zheng Xiaoting, Corwin Sullivan, Wang Xiaoli, Xing Lida, Wang Yan, Zhang Xiaomei, Jingmai O'Connor, Zheng Fucheng Zhang and Pan Yanhong.

Its binomial name, Yi qi, is also the shortest possible under articles 11.8.1 and 11.9.1 of the International Code of Zoological Nomenclature, at four letters.

Yi qi is known only from a single partial skeleton (holotype specimen STM 31-2) currently in the collections of the Shandong Tianyu Museum of Nature [zh].

It is largely articulated, including the skull, lower jaws, neck and limb bones but lacking most of the backbone, pelvis and tail.

This styliform, an adaptation to help support the membrane, may have been a newly evolved wrist bone, or a calcified rod of cartilage.

The greater glider, and the prehistoric gliding rodent Eomys quercyi, also have a similarly long cartilaginous styliform element.

Unlike other paravian dinosaurs, they seem to have replaced bird-like feathers with membranous wings, in what may have been one of many independent evolutionary experiments with flight close to the origin of birds.

That the arm could in principle function as a wing, is shown by being longer than the already elongated hindlimb and the sufficient thickness of its long bones.

While it is possible that some form of flapping flight was also used by this animal, the lack of evidence for large pectoral muscles—the deltopectoral crest of the humerus being small—and the cumbersome nature of the styliform, make it more likely that Yi qi was an exclusive glider.

The bat model has a loading typical for shore birds, though again their wingspan is (much) larger while their aspect ratio to the contrary is higher.

The poor gliding abilities of scansoriopterygids like Yi and Ambopteryx along with their difficulty to take-off, would have made them highly susceptible to be out-competed by more capable aerial vertebrates.

The ecosystem preserved in the Tiaojishan Formation is a forest dominated by bennettitales, ginkgo trees, conifers, and leptosporangiate ferns.

These forests surrounded large lakes in the shadow of active volcanoes, ash from which was responsible for the remarkable preservation of many of the fossils.

[5] Other vertebrate fossils found in the same rock quarry as Yi qi, which would have been close contemporaries, included salamanders like Chunerpeton tianyiensis, the flying pterosaurs Changchengopterus pani, Dendrorhynchoides mutoudengensis, and Qinglongopterus guoi, dinosaurs like Tianyulong confuciusi, basal birds like Anchiornis huxleyi, Caihong juji, and Eosinopteryx brevipenna, and finally as the early gliding[6] mammaliaform species Arboroharamiya jenkinsi.