| Yutyrannus | |
|---|---|
.jpg) | |
| Restored skeletons mounted in fighting poses | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Tyrannosauroidea |
| Family: | †Proceratosauridae |
| Genus: | †Yutyrannus Xuet al., 2012 |
| Species: | †Y. huali |
| Binomial name | |
| †Yutyrannus huali Xuet al., 2012 | |
Yutyrannus (Simplified Chinese : 华丽羽王龙Traditional Chinese : 華麗羽王龍Pinyin : Huà Lì Yǔ Wáng Lóng meaning "feathered tyrant") is agenus ofproceratosauridtyrannosauroid dinosaur which contains a single knownspecies,Yutyrannus huali. This species lived during the earlyCretaceous period in what is now northeasternChina.[1] Threefossils ofYutyrannus huali — all found in the rock beds ofLiaoning Province — are the largest-known dinosaur specimens that preserve direct evidence offeathers.[2]
Yutyrannus huali was named and scientifically described in 2012 byXu Xinget al. The name is derived fromMandarin Chineseyǔ (羽, "feather") and Latinised Greektyrannos (τύραννος, "tyrant"), a reference to its classification as a feathered member of theTyrannosauroidea. Thespecific name consists of the Mandarinhuáli (华丽 simplified, 華麗 traditional, "beautiful"), in reference to the perceived beauty of theplumage.[1]
Yutyrannus is known from three nearly complete fossil specimens (an adult, a subadult and a juvenile) acquired from a fossil dealer who claimed all three had their provenance in a single quarry at Batu Yingzi inLiaoning Province, China. They were thus probably found in a layer of theYixian Formation, dating from theAptian, approximately 125 million years old.[1] The specimens had been cut into pieces about the size of bath mats, which could be carried by two people.[3]
Theholotype, ZCDM V5000, is the largest specimen, consisting of a nearly complete skeleton with a skull, compressed on a slab, of an adult individual. Theparatypes are the two other specimens: ZCDM V5001 consisting of a skeleton of a smaller individual and part of the same slab as the holotype; and ELDM V1001, a juvenile estimated to have been eight years younger than the holotype. The fossils are part of the collections of theZhucheng Dinosaur Museum and theErlianhaote Dinosaur Museum but have been prepared by theInstitute of Vertebrate Paleontology and Paleoanthropology, under the guidance of Xu.[1]
Yutyrannus was a largebipedal predator. The holotype and oldest-known specimen has an estimated length of 9 metres (29.5 ft) and an estimated weight of about 1,414 kilograms (3,117 lb).[1] In 2016,Gregory S. Paul gave lower estimations of 7.5 metres (24.6 ft) and 1.1 tonnes (1.2 short tons).[4] Its skull has an estimated length of 90.5 centimetres (35.6 in). The skulls of the paratypes are 80 centimetres (31 in) and 63 centimetres (25 in) long and their weights have been estimated at 596 kilograms (1,314 lb) and 493 kilograms (1,087 lb), respectively.[1]
The describers established some diagnostic traits ofYutyrannus, in which it differs from its direct relatives. The snout features a high midline crest, formed by thenasals and thepremaxillae and which is covered by large pneumatic recesses. Thepostorbital bone has a small secondary process, jutting into the upper hind corner of the eye socket. The outer side of the main body of the postorbital is hollowed out. In the lower jaw, the external mandibular fenestra, the main opening in the outer side, is mainly located in thesurangular.[1]
The described specimens ofYutyrannus contain direct evidence of feathers in the form of fossil imprints. The feathers were long, up to 20 centimetres (7.9 in), and filamentous. Because the quality of the preservation was low, it could not be established whether the filaments were simple or compound, broad or narrow. The feathers covered various parts of the body. With the holotype they were present on the pelvis and near the foot. Specimen ZCDM V5000 had feathers on the tail pointing backwards under an angle of 30 degrees with the tail axis. The smallest specimen showed 20-centimetre-long (7.9 in) filaments on the neck and 16-centimetre-long (6.3 in) feathers at the upper arm.[1] While it has been known since 2004, upon the description ofDilong, that at least some tyrannosauroids possessed filamentous "stage 1" feathers,[5] according to the feather typology ofRichard Prum,Y. huali is currently the largest-known species of dinosaur with direct evidence of feathers, forty times heavier than the previous record holder,Beipiaosaurus.[1][6]
Based on the distribution of the feathers, they may have covered the whole body and served inregulating temperature, given the rather cold climate of the Yixian with an average annual temperature of 10 °C (50 °F). Alternatively, if they were restricted to the regions in which they were found, they may have served as display structures. In addition, the two adult specimens had distinctive, "wavy" crests on their snouts, on both sides of a high central crest, which were probably used for display. The presence of feathers on a large basal tyrannosauroid suggests the possibility that later tyrannosaurids were also feathered, even when adult, despite their size.[1] However, scaly skin impressions have been reported from various Late Cretaceous tyrannosaurids (such asGorgosaurus,Tarbosaurus andTyrannosaurus) on parts of the body whereYutyrannus was feathered. Since there is no positive evidence for plumage in tyrannosaurids, some researchers have suggested they may have evolved scales secondarily.[7] If scaly skin was the dominant epidermal trait of later genera, then the extent and nature of the integumentary covering may have changed over time in response to body size, a warmer climate, or other factors.[1]
It was considered possible that the integumentary structures ofYutyrannus might not represent true feathers and represent filamentous structures, being ancestral state to feathers.[8] However, this hypothesis is now considered overturned with subsequent research that verified that the structures on various dinosaurs and pterosaurs were true feathers.[1][6]
To date, allphylogenetic analyses ofYutyrannus relationships have classified it in the groupTyrannosauroidea. An initial analysis of its relationship to other tyrannosauroids showed that it was more primitive thanEotyrannus in the evolutionary tree, but more advanced than tyrannosauroids such asDilong,Guanlong andSinotyrannus. Primitive traits relative to advanced tyrannosaurs included long forelimbs with three fingers and a short foot which was not specialized for running. Advanced traits included a large and deep skull, the outer side of the premaxilla having rotated upwards, a large cuneiform horn on thelacrimal in front of the eye socket, a postorbital process on the back rim of the eye socket, thesquamosal and thequadratojugal forming a large process on the back rim of theinfratemporal fenestra, short dorsal vertebrae, anilium with a straight upper rim and an appending lobe, a large pubic foot and a slenderischium.[1]
In 2016, a phylogenetic analysis conducted by Thomas Carr and Stephen Brusatte re-examined the evolutionary relationships of the Tyrannosauroidea. Their analysis foundYutyrannus to be more basal thanDilong, placing it within the familyProceratosauridae.[9] Their cladogram is shown below:
The knowledge of specimens representing various different ages has allowed paleontologists to determine theontogeny, or change during growth, of this species. During growth the lower legs, feet, ilia and forelimbs became relatively smaller. The skull, on the other hand, grew more robust and deeper.[1]
According to a 2018 study,Yutyrannus had a simplehyoid structure, indicating it had a flattongue, like acrocodile. Based on hyoid bone comparisons between living andextinctarchosaurs, it was determined that all archosaurs would have had fixed tongues, with the exception ofbirds,pterosaurs and certainornithischians.[10]
Because the three known individuals ofYutyrannus were allegedly found together, some paleontologists, including Xu Xing, have interpreted the animal as a pack hunter. Based on the presence ofsauropod material in the quarry in which the three specimens were found, Xu has further speculated thatYutyrannus may have hunted sauropods, and that the three known individuals may have died while doing so.[11] In addition, other sauropod hunting theropods such asMapusaurus are known to have exhibited pack hunting behaviour.[12] The true cause of their death, however, remains unknown.[11] IfYutyrannus did prey on sauropods, it would have been one of two predatory animals known from the Yixian formation capable of doing so, the other being an as-of-yet undescribed large theropod known from a tooth embedded in the rib of aDongbeititan.[13]
Because the locality ofYutyrannus is uncertain, it is unknown what fauna it coexisted with. Age estimates point towardsYutyrannus originating from the Lujiatun or the Jianshangou beds of the Yixian, meaning it would have been contemporaneous of such dinosaurs asPsittacosaurus,Dongbeititan,Sinosauropteryx, andCaudipteryx. Fish such asLycoptera would also have been prevalent. Volcanic eruptions and forest fires appear to have been common in the Yixian, and the environment would have been littered with bodies of water and coniferous plants. The environment would have been comparable to the modern daytemperate rainforests of British Columbia, and would have experienced significant seasonal changes in temperature.[14]
.jpg)
.jpg)
.png)
.jpg)
