Yi (dinosaur)

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Yi
Temporal range:
Middle–Late Jurassic, 164–159  Ma
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Yi qi fossil.jpg
Replica fossil of Y. qi
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family:† Scansoriopterygidae
Genus:† Yi
Xu et al., 2015
Type species
Yi qi
Xu et al., 2015
Species
  • Y. qiXu et al., 2015

Yi is a genus of scansoriopterygid dinosaurs from the Late Jurassic of China. Its only species, Yi qi (Mandarin pronunciation: [î tɕʰǐ] ; from Chinese :翼; pinyin :yì; lit.'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. It was a small, possibly tree-dwelling (arboreal) animal. Like other scansoriopterygids, Yi possessed an unusual, elongated third finger, that appears to have 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 might have resulted in wings similar in appearance to those of bats.

Discovery and naming

Skeletal diagram showing known elements Yi qi Headden.png
Skeletal diagram showing known elements

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. This was confirmed by a CAT scan. The initial study of Yi was published in the journal Nature .

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. They named and described the type species Yi qi. The generic name Yi means "wing" in Mandarin. The specific name qi means "strange". [1] Yi is notable for having the shortest generic name of any dinosaur, containing only two letters. 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. (It shares this distinction with the great evening bat Ia io.)

Description

Size of the type specimen compared with a human Yi scale.png
Size of the type specimen compared with a human

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 ]. 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 380 grams (0.84 lb). [1]

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. [1] 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 both the third finger and 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. It was slightly curved and tapered at its outer end. [1]

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. All these structures were rather stiff. [1] 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. The longest feathers, with a length of about six centimetres, were present behind the upper arm and the shinbone. The metatarsus of the foot had a feather covering also. [1]

Life restoration Yiqi NT.jpg
Life restoration

Small patches of wrinkled 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. [1] 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. [1] This would have given the animal an appearance similar to modern bats, in an example of convergent evolution. [1] [2] 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. [1]

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. [1]

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. [1]

Paleobiology

Life restoration by Emily Willoughby Yi qi restoration.jpg
Life restoration by Emily Willoughby

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. 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. [1]

The authors proposed three main models for the wing configuration. In the "bat model", the styliform element would have pointed straight to the rear, a membrane connecting styliform and torso. This would have resulted in a broad wing. A variant of the bat model might be the "pterosaur model" in which the styliform bone would have been directed obliquely to the outside, with a narrower wing as a result. The second main possibility is the "maniraptor model", in which the styliform element was pointing towards the body, reinforcing the trailing edge of a narrow membrane, possibly widened by feathers, on the top or the underside, sticking out. A last configuration would be the "frog model", the styliform bone enlarging a membranous hand plane, like that used by flying frogs. In this last case, no membrane would have formed an inner wing but possibly the arm feathers would have generated some lift. [1]

A preliminary analysis was made of the flight characteristics of the bat model and the maniraptor model. For both models it was assumed that the wingspan was about sixty centimetres (24 in). The narrow wing of the maniraptor model would have resulted in a 320 cm2 (50 sq in) wing surface with a wing loading of 1.19 g/cm2 (2.4 lb/sq ft). For the broad bat model wing these values would have been 638 cm2 (98.9 sq in) and 0.6 g/cm2 (1.2 lb/sq ft) respectively. In both cases the wing loading is well below the critical 2.5 g/cm2 (25 kg/m2; 5.1 lb/sq ft) upper limit for bird flight. The maniraptor model loading is typical for ducks, though these have a relatively larger wingspan and a lower aspect ratio. 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. A problem for the hypothesis that Yi was specialised for gliding flight, resides in the fact that because of it having a forelimb wing, instead of a gliding skin along its torso as with most gliders, its center of mass seems to be behind its control and main lift surfaces, causing flight instability. This problem might have been lessened by a short fleshy tail and long tail feathers, as known from its relative Epidexipteryx . Its stability might also have been improved by a few flapping movements of its wings. A modern analogue is the kākāpō, that likewise glides from trees but also flaps to control its descent. [1]

In 2020, T. Alexander Dececchi and colleagues found that, though Yi and other scansoriopterygids were gliding arboreal animals, they had notorious deficiencies in flapping behaviors such as WAIR (Wing-assisted incline running) or taking-off from ground compared to other small paravians, and had similar gliding abilities to those of nearly-sized mammalian gliders, such as bats. Their results suggest that scansoriopterygids might have been specialized maniraptorans in mainly closed forests. While the high glide speed and average glide ratios would have been more efficient for travelling across small gaps in the canopy, longer flights would have been less efficient with higher predation risks. 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. Moreover, their likely specialist life-style may have further contributed to this disadvantage. [3]

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, [1] dated to approximately 159 million years ago. [4] 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. [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 . [1]

See also

Related Research Articles

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Archaeopteryx, sometimes referred to by its German name, "Urvogel" is a genus of bird-like dinosaurs. The name derives from the ancient Greek ἀρχαῖος (archaīos), meaning "ancient", and πτέρυξ (ptéryx), meaning "feather" or "wing". Between the late 19th century and the early 21st century, Archaeopteryx was generally accepted by palaeontologists and popular reference books as the oldest-known bird. Older potential avialans have since been identified, including Anchiornis, Xiaotingia, and Aurornis.

<i>Protarchaeopteryx</i> Extinct genus of dinosaurs

Protarchaeopteryx is a genus of turkey-sized feathered theropod dinosaur from China. Known from the Jianshangou bed of the Yixian Formation, it lived during the early Aptian age of the Early Cretaceous, approximately 124.6 million years ago. It was probably a herbivore or omnivore, although its hands were very similar to those of small carnivorous dinosaurs. It appears to be one of the most basal members of the Oviraptorosauria, closely related to Incisivosaurus, or a taxon slightly less closely related to birds than oviraptorosaurs were.

<i>Microraptor</i> Extinct genus of dinosaurs

Microraptor is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation, 125 to 120 million years ago. Three species have been named, though further study has suggested that all of them represent variation in a single species, which is properly called M. zhaoianus. Cryptovolans, initially described as another four-winged dinosaur, is usually considered to be a synonym of Microraptor.

<span class="mw-page-title-main">Maniraptora</span> Clade of dinosaurs

Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, Oviraptorosauria, and Therizinosauria. Ornitholestes and the Alvarezsauroidea are also often included. Together with the next closest sister group, the Ornithomimosauria, Maniraptora comprises the more inclusive clade Maniraptoriformes. Maniraptorans first appear in the fossil record during the Jurassic Period, and survive today as living birds.

<span class="mw-page-title-main">Patagium</span> Membranous structure that assists an animal in gliding or flight

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<i>Yixianosaurus</i> Extinct genus of dinosaurs

Yixianosaurus is a maniraptoran theropod dinosaur genus from the Early Cretaceous of China.

<i>Scansoriopteryx</i> Extinct genus of dinosaurs

Scansoriopteryx is a genus of maniraptoran dinosaur. Described from only a single juvenile fossil specimen found in Liaoning, China, Scansoriopteryx is a sparrow-sized animal that shows adaptations in the foot indicating an arboreal (tree-dwelling) lifestyle. It possessed an unusual, elongated third finger which may have supported a membranous wing, much like the related Yi qi. The type specimen of Scansoriopteryx also contains the fossilized impression of feathers.

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<span class="mw-page-title-main">Paraves</span> Clade of all dinosaurs that are more closely related to birds than to oviraptorosaurs

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<i>Epidexipteryx</i> Extinct genus of dinosaurs

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<i>Anchiornis</i> Extinct genus of dinosaurs

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<i>Eosinopteryx</i> Extinct genus of dinosaurs

Eosinopteryx is an extinct genus of theropod dinosaurs known to the Late Jurassic epoch of China. It contains a single species, Eosinopteryx brevipenna.

<i>Aurornis</i> Extinct genus of dinosaurs

Aurornis is an extinct genus of anchiornithid theropod dinosaurs from the Jurassic period of China. The genus Aurornis contains a single known species, Aurornis xui. Aurornis xui may be the most basal ("primitive") avialan dinosaur known to date, and it is one of the earliest avialans found to date. The fossil evidence for the animal pre-dates that of Archaeopteryx lithographica, often considered the earliest bird species, by about 10 million years.

<i>Serikornis</i> Extinct genus of dinosaurs

Serikornis is a genus of small, feathered anchiornithid dinosaur from the Upper Jurassic Tiaojishan Formation of Liaoning, China. It is represented by the type species Serikornis sungei.

<span class="mw-page-title-main">Anchiornithidae</span> Extinct family of dinosaurs

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<i>Caihong</i> Extinct genus of dinosaurs

Caihong is a genus of small paravian theropod dinosaur from China that lived during the Late Jurassic period.

<i>Ambopteryx</i> Genus of scansoriopterygid dinosaur

Ambopteryx is a genus of scansoriopterygid dinosaur from the Oxfordian stage of the Late Jurassic of China. It is the second dinosaur to be found with both feathers and bat-like membranous wings. Yi, the first such dinosaur, was described in 2015 and is the sister taxon to Ambopteryx. The holotype specimen is thought to be a sub-adult or adult. The specimen is estimated to have had a body length of 32 centimetres (13 in) and a weight of 306 grams (10.8 oz). The genus includes one species, Ambopteryx longibrachium.

Cascocauda is an extinct genus of anurognathid pterosaur from the Late–⁠Middle Jurassic Tiaojishan Formation of Hebei Province, China. The genus contains a single species, C. rong, known from a complete skeleton belonging to a juvenile individual preserved with extensive soft-tissues, including wing membranes and a dense covering of pycnofibres. Some of these pycnofibres appear to be branched, resembling the feathers of maniraptoran theropod dinosaurs, and suggesting that pterosaur pycnofibres may be closely related to feathers in dinosaurs.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Xu, Xing; Zheng, Xiaoting; Sullivan, Corwin; Wang, Xiaoli; Xing, Lida; Wang, Yan; Zhang, Xiaomei; O’Connor, Jingmai K.; Zhang, Fucheng & Pan, Yanhong (7 May 2015). "A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings". Nature. 521 (7550): 70–73. Bibcode:2015Natur.521...70X. doi:10.1038/nature14423. PMID   25924069. S2CID   205243599.
  2. ↑ Wilford, John Noble (April 29, 2015). "Small Jurassic Dinosaur May Have Flown Without Feathers". The New York Times . Archived from the original on 2 November 2017. Retrieved April 29, 2015.
  3. ↑ Dececchi, T. Alexander; Roy, Arindam; Pittman, Michael; Kaye, Thomas G.; Xu, Xing; Habib, Michael B.; Larsson, Hans C. E.; Wang, Xiaoli & Zheng, Xiaoting (2020). "Aerodynamics Show Membrane-Winged Theropods Were a Poor Gliding Dead-end". iScience. 23 (101574): 101574. Bibcode:2020iSci...23j1574D. doi: 10.1016/j.isci.2020.101574 . PMC   7756141 . PMID   33376962.
  4. ↑ Yu, Zhiqiang; He, Huaiyu; Li, Gang; Deng, Chenglong; Wang, Hai-Bing; Zhang, Xinxin; Yang, Qing; Xia, Xiao-Ping; Zhou, Zhonghe & Zhu, Rixiang (2019). "SIMS U-Pb geochronology for the Jurassic Yanliao Biota from Bawanggou section, Qinglong (northern Hebei Province, China)". International Geology Review. 63 (3): 265–275. doi:10.1080/00206814.2019.1707127. S2CID   212957272.
  5. ↑ Wang, Yongdong; Saiki, Ken'ichi; Zhang, Wu & Zheng, Shaolin (2006). "Biodiversity and palaeoclimate of the Middle Jurassic floras from the Tiaojishan Formation in western Liaoning, China". Progress in Natural Science. 16 (9): 222–230. doi:10.1080/10020070612330087A (inactive 31 January 2024). Archived from the original on 13 February 2021. Retrieved 29 May 2020.{{cite journal}}: CS1 maint: DOI inactive as of January 2024 (link)
  6. ↑ Han, Gang; Mao, Fangyuan; Bi, Shundong; Wang, Yuanqing & Meng, Jin (2017). "A Jurassic gliding euharamiyidan mammal with an ear of five auditory bones". Nature. 551 (7681): 451–456. Bibcode:2017Natur.551..451H. doi:10.1038/nature24483. PMID   29132143. S2CID   4466953.
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