Yutyrannus

Yutyrannus (meaning "feathered tyrant") is a genus of proceratosaurid tyrannosauroid dinosaur which contains a single known species, Yutyrannus huali. This species lived during the early Cretaceous period in what is now northeastern China. Three fossils of Yutyrannus huali — all found in the rock beds of Liaoning Province — are the largest-known dinosaur specimens that preserve direct evidence of feathers.

Yutyrannus huali was named and scientifically described in 2012 by Xu Xing et al. The name is derived from Mandarin Chinese yǔ (羽, "feather") and Latinised Greek tyrannos (τύραννος, "tyrant"), a reference to its classification as a feathered member of the Tyrannosauroidea. The specific name consists of the Mandarin huáli (华丽 simplified, 華麗 traditional, "beautiful"), in reference to the perceived beauty of the plumage.

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 in Liaoning Province, China. They were thus probably found in a layer of the Yixian Formation, dating from the Barremian, approximately 125 million years old.The specimens had been cut into pieces about the size of bath mats, which could be carried by two people.

Yutyrannus was a large bipedal 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.

The describers established some diagnostic traits of Yutyrannus, in which it differs from its direct relatives. The snout features a high midline crest, formed by the nasals and the premaxillae and which is covered by large pneumatic recesses. The postorbital 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 the surangular.

The described specimens of Yutyrannus 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 of Dilong, that at least some tyrannosauroids possessed filamentous "stage 1" feathers,[5] according to the feather typology of Richard 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.

Based on the distribution of the feathers, they may have covered the whole body and served in regulating 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 as Gorgosaurus, Tarbosaurus and Tyrannosaurus) on parts of the body where Yutyrannus was feathered. Since there is no positive evidence for plumage in tyrannosaurids, some researchers have suggested they may have evolved scales secondarily. 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.

It was considered possible that the integumentary structures of Yutyrannus might not represent true feathers and represent filamentous structures, being ancestral state to feathers. However, this hypothesis is now considered overturned with subsequent research that verified that the structures on various dinosaurs and pterosaurs were true feathers.