| Yi qi|
Temporal range: Late Jurassic, 160Ma
Xu et al., 2015
|Species:||† Y. qi|
| Yi qi|
Xu et al., 2015
Yi is a genus of gliding scansoriopterygid dinosaurs. Its only species, Yi qi (Mandarin pronunciation: [î tɕʰǐ]) (from Chinese: 翼; pinyin: yì; literally: "wing" and 奇; qí; "strange"), is known from a single fossil specimen of an adult individual found in late Jurassic period rocks in Hebei, China. It was a small, tree-dwelling (arboreal) animal, and glided from branch to branch. Like other scansoriopterygids, it possessed an unusual, elongated third finger, that helped to support a membranous gliding plane made of skin. The planes of Yi qi were also supported by a long, bony strut attached to the wrist. This modified wrist bone and membrane-based plane is unique among all known dinosaurs, and made Yi qi similar in appearance to mammals such as sugar gliders.
Yi qi is known only from a single partial skeleton (STM 31-2) currently in the collections of the Shandong Tianyu Museum of Nature. It was a relatively small animal, estimated to weigh about 380 grams (0.84 lb).
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 upper front teeth being the largest and slightly forward-pointing, and the front lower teeth were angled even more strongly forward. The long, slender forelimbs were similar, overall, to those of most other paravian dinosaurs. Like other scansoriopterygid dinosaurs, the first finger was shortest and the third was the longest. Unlike all other known dinosaurs, a long, pointed wrist bone known as a "styliform element", exceeding the ulna in length, extended backward from the forelimb bones. This styliform, an adaptation to help support the membrane, may have been a newly evolved wrist bone, or a calcified rod of cartilage.
The only known specimen of Yi qi preserved a heavy covering of feathers. Unusually based on its classification as an advanced theropod in the clade Pennaraptora (a group containing theropods with advanced, bird-like feathers), the feathers were all very simple in structure and "paintbrush-like", with long quill-like bases topped by sprays of thinner filaments. The feathers covered most of the body, starting near the tip of the snout. The head and neck feathers were long and formed a thick coat, and the body feathers were even longer and denser, making it difficult for scientists to study their detailed structure. Small patches of skin were also preserved between the fingers and the styliform bone, indicating that unlike all other known dinosaurs, the planes of Yi qi were formed by a skin membrane rather than flight feathers. The membrane stretched between the shorter fingers, the elongated third finger, the styliform bone, and possibly connected to the torso, though the inner part of the wing membrane was not preserved in the only known fossil. This would have given the animal an appearance similar to modern sugar gliders, in an example of convergent evolution. However, in bats, the membrane stretches between the fingers, not a styliform wrist bone. Styliform bones are also found in the wings of some modern gliding animals like flying squirrels, the Greater glider, and the prehistoric gliding rodent Eomys quercyi.
The strange membranous wings of Yi qi are unique among dinosaurs and difficult to interpret. 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, and the cumbersome nature of the styliform, make it more likely that Yi qi was an exclusive glider. At best, the researchers who conducted the initial study of the only known Yi specimen concluded that its mode of flight should be considered uncertain.
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 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, dated to between 165 and 153 million years ago. 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, as well as the early tree-dwelling mammal species Arboroharamiya jenkinsi.
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). 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. The initial study of Yi was published in the journal Nature and appeared on the Internet 29 April 2015. 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.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 Xu, X.; Zheng, X.; Sullivan, C.; Wang, X.; Xing, L.; Wang, Y.; Zhang, X.; o’Connor, J. K.; Zhang, F.; Pan, Y. (2015). "A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings". Nature. doi:10.1038/nature14423.
- ↑ Wilford, John Noble (April 29, 2015). "Small Jurassic Dinosaur May Have Flown Without Feathers". New York Times. Retrieved April 29, 2015.
- ↑ Zhang, H.; Wang, M.; Liu, X. (2008). "Constraints on the upper boundary age of the Tiaojishan Formation volcanic rocks in West Liaoning-North Hebei by LA-ICP-MS dating". Chinese Science Bulletin 53 (22): 3574. doi:10.1007/s11434-008-0287-4.
- ↑ Wang Yongdonga, Saiki Ken'ichi, Zhang Wuc & Zheng Shaolin (2006). "Biodiversity and palaeoclimate of the Middle Jurassic floras from the Tiaojishan Formation in western Liaoning, China". Progress in Natural Science 16: 222–230. doi:10.1080/10020070612330087.