| Tsintaosaurus | |
|---|---|
 | |
| Holotype skull with broken crest | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Subfamily: | †Lambeosaurinae |
| Tribe: | †Tsintaosaurini |
| Genus: | †Tsintaosaurus Young,1958[1] |
| Type species | |
| †Tsintaosaurus spinorhinus | |
Tsintaosaurus (/sɪntaʊˈsɔːrəs/;sic for theold transliteration "Tsingtao",[2] meaning "Qingdao lizard") is agenus ofhadrosauriddinosaur fromChina. It was about 8.3 metres (27 ft) long and weighed 2.5 tonnes (2.8 short tons).[3] Thetype species isTsintaosaurus spinorhinus, first described by Chinese paleontologistC. C. Young in 1958.
As a hadrosaur,Tsintaosaurus had the characteristic 'duck bill' snout and a battery of powerfulteeth 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 and traveled in herds.
In 1950, atHsikou, nearChingkangkou, inLaiyang,Shandong, in the eastern part ofChina, various remains of large hadrosaurids were uncovered. In 1958 these were described by Chinese paleontologistYang Zhongjian ("C.C. Young") as thetype speciesTsintaosaurus spinorhinus. The generic name is derived from the city ofQingdao, earlier often transliterated as "Tsintao". Thespecific name means "with a nose spine", fromLatinspina, and Greek ῥίς,rhis, "nose", in reference to the distinctive crest on the snout.[1]
Theholotype, IVPP AS V725, was discovered in a layer of theJingangkou Formation, part of theWangshi Group dating from theCampanian. It consists of a partial skeleton with skull. Theparatype 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 toTsintaosaurus, others were named as aTanius chingkankouensis Yang 1958; also aTanius laiyangensis Zhen 1976 exists. The latter two species are today either consideredjunior synonyms ornomina dubia. Later researchers would refer a larger part of the material toTsintaosaurus.
Tsintaosaurus was originally reconstructed with aunicorn-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 B. Weishampel andJack Horner cast doubt on the presence of the crest, suggesting that it was actually a brokennasal 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 hadrosaurTanius. However, in 1993Éric 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 andTsintaosaurus is likely a distinct genus.[4]
A new reconstruction in 2013, byAlbert Prieto-Márquez andJonathan Wagner and based on the identification of specimen IVPP V829, a praemaxilla, as aTsintaosaurus 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.[5]
The new reconstruction by Prieto-Márquez and Wagner also led to a new hypothesis about the internal air passages of the crest. Yang had assumed that the tubular hollowing in the preserved part of the holotype would have served as the main intake of air. This was rejected by Prieto-Márquez and Wagner who pointed out that the tube was closed at its lower end and that with lambeosaurines in general the air passages are located in a more forward position, the bony nostrils being completely enclosed by the praemaxillae. They assumed thatTsintaosaurus would have had a standard lambeosaurine arrangement in the snout, the air, when inhaling, entering the skull through the pairedpseudonares, the "fake nostrils" of the praemaxillae behind the upper beak. From there the air would have been transported through paired passages below the median processes of the praemaxillae to the top of the crest, subsequently entering a common median chamber within the lobe. The rear of the chamber was formed by the nasal bones and probably homologous to thenasal cavity. The chamber was divided into two smaller cavities, one at the front, the other at the rear, by curved median processes of the praemaxillae, forming hooks around a passage between the cavities. From the rear cavity the air was transported to below, towards the internal skull cavity. Although it is usually assumed that a single passage served for this purpose, Prieto-Márquez and Wagner saw indications in the form of the nasal that there were paired downward passages, to the inside of the lateral processes of the praemaxillae. From this they concluded that the entire airflow was likely separated, the common medium chamber probably being divided into a left and right section by a cartilaginous septum.[5]
The conclusion that the tubular structure in the rear nasal bones was not an air passage, forced Prieto-Márquez and Wagner to find an alternative explanation of its function. They suggested that it would have served to lessen the weight of the crest, such a tube combining relative strength with a low bone mass.Tsintaosaurus would have differed in this from more derived lambeosaurines, which have a front extension of the frontal bone, in the form of a bone sheet, supporting the crest.[5]
Apart from the crest, Prieto-Márquez and Wagner identified several other distinctive traits (autapomorphies) ofTsintaosaurus. 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. Thesupratemporal fenestra is, transversely, wider than long.[5]
Tsintaosaurus may form aclade inLambeosaurinae with the European generaPararhabdodon andKoutalisaurus (probable synonym ofPararhabdodon).[6]
The position ofTsintaosaurus in the evolutionary tree according to a 2013 study by Prieto-Márquez e.a. is indicated by this cladogram:[7]
A study of dinosaur eggs in successive layers of the Wangshi Series of Shandong province, of which the Jingangkou Formation is the most recent layer, shows that the region was one of high dinosaur diversity and that the climate had become drier from the preceding Jiangjunding Formation.[8]
