Yi (dinosaur)

The first and only known specimen of Yi qi was a fossil of an adult individual found by a farmer, Wang Jianrong, in a quarry near Mutoudeng Village (Qinglong County, Hebei). Wang sold the fossil to the Shandong Tianyu Museum of Nature in 2007, at which point Ding Xiaoqing, a technician at the museum, began further preparation of the fossil. Because many of the unique features and soft tissues of the specimen were uncovered by museum staff during preparation rather than amateur fossil sellers before the purchase, the scientists who studied it were confident that the specimen was authentic and unaltered, which was confirmed by a CAT scan. The initial study of Yi was published in the journal Nature. ==Description==

Yi qi is known only from a single partial skeleton (holotype specimen STM ) currently in the collections of the . The fossil was compressed and is visible on a stone plate and a counterplate. It is largely articulated, including the skull, lower jaws, neck, and limb bones, but lacking most of the backbone, pelvis, and tail. Yi was a relatively small animal, estimated to weigh about . Like other scansoriopterygids, the head was short and blunt-snouted, with a downturned lower jaw. Its few teeth were present only in the tips of the jaws, with the four upper front teeth per side being the largest and slightly forward-pointing, and the front lower teeth being angled even more strongly forward. However, in bats, the membrane stretches between the fingers only, no styliform wrist bone being present. Ossified styliform bones are found, however, in the wings of some modern gliding animals like flying squirrels. The greater glider, and the prehistoric gliding rodent Eomys quercyi, also have a similarly long cartilaginous styliform element. On twelve positions the fossil was checked by an electron microscope for the presence of melanosomes, pigment-bearing organelles. All nine feather locations showed eumelanosomes. In the head feathers also phaeomelanosomes were present. On the membranes, only one observation had a positive result, of phaeomelanosomes. The eumelanosomes of the calf feathers were exceptionally large. ==Classification==

Yi was placed in the Scansoriopterygidae, a group of maniraptoran theropods. A cladistic analysis failed to resolve its exact relationships with the other known scansoriopterygids, Epidendrosaurus and Epidexipteryx. In the analysis the Scansoriopterygidae was recovered as the most basal clade of the Paraves. ==Paleobiology==

Yi qi, and presumably other scansoriopterygids, possessed a type of wing unknown among any other prehistoric bird relatives. 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. The membranous wings of Yi qi are unique among dinosaurs and difficult to interpret. 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. Also it is hard to explain the styliform element outside a flight context. The presence of a long styliform bone adding support to the membrane, found only in other animals that glide, suggests that Yi qi was specialized for gliding flight. 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 only indication of powered flight comes from the researchers who conducted the initial study of the only known Yi specimen, who concluded that its mode of flight should be considered uncertain. ==Paleoecology==

The only known Yi qi fossil was found in rocks assigned to the Tiaojishan Formation, dating to the Callovian-Oxfordian age of the Middle-Late Jurassic, This is the same formation (and around the same age) as the other known scansoriopterygids Epidexipteryx and Scansoriopteryx. 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. Based on the Tiajishan's plant life, its climate would have been subtropical to temperate, warm and humid. 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 mammaliaform species Arboroharamiya jenkinsi. ==See also==