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 Batuyingzi in Liaoning Province, China. They thus probably were found in a layer of the Yixian Formation, dating from the Aptian, about 125 million years old. The specimens had been cut into pieces about the size of bath mats, which could be carried by two people.
The holotype, ZCDM V5000, is the largest specimen,
consisting of a nearly complete skeleton with skull, compressed on a slab, of an adult individual. The paratypes 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 the Zhucheng Dinosaur Museum and the Erlianhaote Dinosaur Museum but have been prepared by the Institute of Vertebrate Paleontology and Paleoanthropology, under guidance of Xu.
Yutyrannus was a gigantic bipedal predator. The holotype has a known length of 9 metres (30 ft) and an estimated weight of 1,414 kg (3,120 lb). Its skull has an estimated length of 905 millimetres. The skulls of the paratypes are eighty and sixty-three centimetres long and their weights have been estimated at 596 and 493 kilogrammes 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 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.
While it has been known since 2004, upon the description of Dilong, that at least some tyrannosaurs possess filamentous “stage 1″ feathers, 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. The feathers were long, up to twenty centimetres, 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 the foot. Specimen ZCDM V5000 had feathers on the tail pointing backwards under an angle of 30° with the tail axis. The smallest specimen showed twenty-centimetre-long filaments on the neck and sixteen-centimetre-long feathers at the upper arm. Based on this distribution, 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. 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.
Yutyrannus was by the describers assigned to the Tyrannosauroidea in 2012. A cladistic analysis showed it occupied a rather basal position, below Eotyrannus in the evolutionary tree, but above forms such as Dilong, Guanlong and Sinotyrannus. Basal traits included long forelimbs with three fingers and a short, non-arctometatarsalian, foot. Derived traits include a large and deep skull, the outer side of the premaxilla having rotated upwards, a large cuneiform horn on the lacrimal in front of the eye socket, a postorbital process on the back rim of the eye socket, the squamosal and the quadratojugal forming a large process on the back rim of the infratemporal fenestra, short dorsal vertebrae, an ilium with a straight upper rim and an appending lobe, a large pubic foot and a slender ischium.
Darren Naish pointed out that the species resembles carcharodontosaurs and allosaurus such as Concavenator, especially in some for a tyrannosaurs unusual features of the skull, such as the pneumatic recesses on the snout crest, the secondary postorbital process and the form of the postorbital boss.
The presence of specimens of a different age allows to determine the ontogeny. During growth the lower legs, the feet, ilium and the forelimbs became relatively smaller. The skull on the other hand, grew more robust and deeper.
In popular culture
- In the mobile game Jurassic Park Builder, you can buy a Yutyrannus.
- in Fossil Fighters Frontier, Yutyranus elemental AR cards can be scanned.