Tsintaosaurus

Tsintaosaurus (/tʃɪŋdaʊˈsɔrəs/; meaning "Qingdao lizard", after the old transliteration "Tsingtao") [1] is a genus of hadrosaurid dinosaur from China. It was about 10 metres (33 ft) long, 3.6 metres (12 ft) tall and weighed 3 tons.[2] The type species is Tsintaosaurus spinorhinus, first described by Chinese paleontologist C. C. Young in 1958.

A hadrosaur, Tsintaosaurus had a characteristic 'duck bill' snout and a battery of powerful teeth which it used to chew vegetation. It usually walked on all fours, but could rear up on its hind legs to scout for predators and flee when it spotted one. Like other hadrosaurs, Tsintaosaurus probably lived in herds.

Discovery and naming
In 1950, at Hsikou, near Chingkangkou, in Laiyang, Shandong, in the eastern part of China, various remains of large hadrosaurids were uncovered. In 1958 these were described by Chinese paleontologist Yang Zhongjian ("C.C. Young") as the type species Tsintaosaurus spinorhinus. The generic name is derived from the city of Qingdao, earlier often transliterated as "Tsintao". The specific name means "with a nose spine", from Latin spina, and Greek ῥίς, rhis, "nose", in reference to the distinctive crest on the snout.[3]

The holotype, IVPP AS V725, was discovered in a layer of the Jingangkou Formation dating from the Campanian. It consists of a partial skeleton with skull. The paratype is specimen IVPP V818, a skull roof. In the same area some additional partial skeletons and a large number of disarticulated skeletal elements were found. Some of these were by Yang referred to Tsintaosaurus, others were named as a Tanius chingkankouensis Yang 1958; also a Tanius laiyangensis Zhen 1976 exists. The latter two species are today either considered junior synonyms or nomina dubia. Later researchers would refer a larger part of the material to Tsintaosaurus.

Crest
Tsintaosaurus was originally reconstructed with a unicorn-like crest on its skull. The crest, as preserved, consists of an about forty centimetres long process, protruding almost vertically from the top of the rear snout. The structure is hollow and seems to have a forked upper end. Comparable structures with related species are unknown: they possess more lobe-like crests. In 1990, David Weishampel and Jack Horner cast doubt on the presence of the crest, suggesting that it was actually a broken nasal bone from the top of the snout distorted upward by a crushing of the fossil. Their study further suggested that, without the distinctive crest to distinguish it, Tsintaosaurus was actually a synonym of the similar but crestless hadrosaur Tanius. However, in 1993 Eric Buffetaut e.a., after a renewed investigation of the bones themselves, concluded that the crest was neither distorted nor an artefact of restoration; besides, a second specimen with an upright crest part had since been discovered, indicating that the crest was indeed real and Tsintaosaurus is likely a distinct genus.[4]

A new reconstruction in 2013, by Albert Prieto-Márquez and Jonathan Wagner and based on the identification of specimen IVPP V829, a praemaxilla, as a Tsintaosaurus element, came to the conclusion that the unicorn-like bone was just the rear part of a larger cranial crest that started from the tip of the snout. The front of the crest would have been formed by ascending processes of the praemaxillae. These had expanded rhomboid contact facets with the expanded upper parts of the crest processes of the nasal bones, forming the rear of the crest. The rear base of the crest was covered by outgrowths of the prefrontals. The fused nasal bones would have formed a hollow tubular structure. The height of the crest would have exceeded that of the rear skull, measured along the quadrates. Though largely vertical, the crest is directed slightly to the rear; the forward inclination of the holotype crest would be the result of a distortion of the fossil.

Other distinctive traits
Apart from the crest, Prieto-Márquez and Wagner identified several other distinctive traits (autapomorphies) of Tsintaosaurus. The rim of the upper beak is rounded and thick, wider than the transverse width of the front depression around the nostrils. As far as this depression is situated on the praemaxillae, it is at each side divided lengthwise by two ridges obliquely continuing to below and sideways. Internally, the fused nasal bones form a bony block in front of the braincase. The rear of the nasal bone is clipped by front extensions of the frontal bone, the topmost of which is elevated relative to the skull roof. The ascending branches of the praemaxillae have internal processes pointing to behind, below and slightly inside, dividing a shared chamber at the midline. The prefrontal possesses a flange, continuing from the lower part of the lacrimal bone to the lower part of the ascending process of the prefrontal, and connecting to a process on the side of the praemaxilla to form an elevation on the side of the crest base. The side and the underside of the prefrontal show deep vertical grooves. The supratemporal fenestra is, transversely, wider than long.

Classification
Tsintaosaurus may form a clade in Lambeosaurinae with the European genera Pararhabdodon and Koutalisaurus (probable synonym of Pararhabdodon).[6]

The position of Tsintaosaurus in the evolutionary tree according to a 2013 study by Prieto-Márquez e.a. is indicated by this cladogram: >