Yinlong

Skull of Yinlong

• China

Yinlong is a genus of bird Beck dinosaur ( Ornithischia ) from the group of ceratopsians. He is the oldest and most primitive known members of this group. It also shows some characteristics of the Pachycephalosauria and thus underpins the presumed close relationship of these two groups of dinosaurs. Yinlong lived in the Upper Jurassic in East Asia. Only species described is downsi Y. Xu et al., 2006.

Features

From Yinlong been a single, complete down to the tip of the tail specimen was found. But it had probably not yet fully grown a length of 1.2 meters, was. The hind legs were heavy and strong, the front legs, which reached only 40 % of the length of the hind limbs, thin and delicate. Presumably Yinlong moved away biped.

There was a Rostralknochen, which clearly classifies this dinosaur as a representative of Ceratopsia At the top of the upper jaw. The squamosal ( squamosal ) is characterized by a series of small bony bumps, which is also a feature of Pachycephalosauria. It forms a narrow neck shield, as opposed to the later ceratopsians the parietal ( parietal ) is not involved in the neck shield.

At the premaxillary bone ( premaxilla ) are per side and three on the upper jaw (maxilla ) per page 13 teeth. The teeth of the premaxillary bone are significantly larger, the second tooth is slightly serrated. The maxillary teeth are close together and are chisel-shaped. Due to the closed jaw teeth of the lower jaw can be hardly seen, but the front is much smaller than the rear.

In the area of the fuselage were seven gastroliths, with 1 to 1.5 centimeters in diameter, found everyone. Compared with the proportions of the animal they are strikingly large, similar to the Psittacosauridae.

Discovery and dating

The fossil remains of Yinlong were discovered in the Shishugou Formation in the Djungarian pool in the Chinese province of Xinjiang and first described in 2006 by Xu Xing. The genus name is derived from the Chinese words Yǐn (Chinese隐/隐'hidden' ) and Lóng (龙/龙, dragon '). This is an allusion to the film Crouching Tiger, Hidden Dragon, which was partially filmed near the locality. Long ( = " Dragon" ) is also a common name component in dinosaurs that have been found in China, such as Dilong or guanlong. Type species and only known species is Y. downsi, the specific epithet honors the deceased shortly before designation paleontologists Will Downs.

The finds are dated to the early Upper Jurassic in the Oxfordian to an age of about 163-157 million years. Yinlong is the oldest -known ceratopsian, which this group is about 20 million years older than previously thought.

System

Characteristics such as the Rostralknochen classify Yinlong clearly representing the Ceratopsia. From other Ceratopsia but it differs inter alia by a proportionately smaller head, the reduced width of Jugale ( a skull bone ), the exclusion of the parietal bone from the neck shield and other features in the structure of the skull. Therefore, the first describer classify him as basalsten representative of this dinosaur group.

The same time, Yinlong but also features the Pachycephalosauria on, a predominantly common in the Upper Cretaceous dinosaur group stubborn. Even before the discovery Yinlongs were Ceratopsia and Pachycephalosauria related as closely and have been summarized as Marginocephalia. Due to the high specialization of both groups of dinosaurs, this relationship was weak but so far secured only by morphological features. According to Erstbeschreibern the monophyly of Marginocephalia is clearly borne out by the Fund of Yinlong.

The second, but surprising conclusion of the describer is that Yinlong also has similarities with the Heterodontosauridae. In most recent classifications, as well as in Weishampel et al. (2004), the Heterodontosauridae a form- rich dinosaur group to be reckoned with, among others, Iguanodon and the Hadrosauridae be attributed to ornithopods. According to these classifications ornithopods and Marginocephalia regarded as sister groups. Xu et al. however, summarize the Marginocephalia and Heterodontosauridae as Heterodontosauriformes and perform skull features ( the temporal region and the region in front of the eye) and features in the construction of the teeth (such as the enlarged teeth of the premaxillary bone) as similarities. Xu et al. present a phylogenetic analysis, according to which the Heterodontosauriformes are embedded in the ornithopods. That would make the ornithopods in the traditional sense (without the Marginocephalia ) to a paraphyletic group. Whether passing through this point of view, remains to be seen.