Xianglong

Live reconstruction of Xianglong

• Liaoning, China ( Yixian Formation)

• Xianglong zhaoi

Xianglong was a to the iguana -like ( Iguania ) scoring genus of Squamata from the Lower Cretaceous of China. The only known species is Xianglong zhaoi. It is similar to the recent kite ( Draco ), which Xianglong is however not closely related. The first description was by Li Pipeng et al. in 2007. Previously, the holotype ( specimen number 000666 LPM ) is the only known fossil of Xianglong. It is visible on a main and a back plate as well as complete and well preserved. Kept it in the Paleontological Museum of Liaoning.

With a plane spanned by elongated ribs patagium the reptile had the ability to glide. The genus name comes from the Chinese Xianglong and means something like "Flying Dragon", the epithet honors zhaoi Zhao Dayu, one of the founders of the Paleontological Museum in Liaoning.

Geological Background

The fossil was discovered in the Zhuanchengzi layer near the village Zhuangchengzi near the large village Yizhou in China's Liaoning Province. The Zhuanchengzi layer is dated to 122 million to 120 million years, sometimes for 145 bis 140 million years be specified. The Zhuangchengzi layer is part of the Yixian Formation, a formation of the Jehol Group. It consists largely of siliciclastic sedimentary rocks that came in lakes for deposition. Individual layers of tuff and basalt are the result of volcanic activity. The Yixian Formation is known for their exceptional fossil preservation, especially for the tradition of soft-tissue structures (for Xianglong the airplane skin) famous, why she and the Jehol Group are referred to collectively as Konservatlagerstätte. Especially the numerous finds of feathered dinosaurs like Sinosauropteryx and early birds like Conficiusornis have done in the last twenty years to a sudden increase of knowledge about the phylogeny of birds in the Mesozoic era.

The climate at the time of deposition was probably characterized by a change from warm, humid rainy seasons and dry seasons. Away from the lake areas the climate was generally dry. Conifers dominated the vegetation; furthermore came before ferns, horsetails, club mosses and rare early angiosperms. The good preservation of the Yixian fossils can be explained by its rapid embedding: Dead animals sank without long transport by rivers to the bottom of a lake from and were covered by fine-grained sediment. Land animals such as Xianglong remained in the same way as Lake residents receive and are found in the same layers. The most and best preserved fossils are found directly under the layers volcanically formed, as these rapidly solidified deposits underlying layers effectively sections of oxygen and so decomposition prevented by other organisms and decay.

Physique

The information on the morphology of this Gleitreptils are based on the holotype ( specimen number 000666 LPM ), the only known fossil of Xianglong zhaoi. The specimen was probably not yet fully grown, which can be identified through only slightly ossified tarsal bones and the absence of ossified carpal bones.

The fossil found is 15.5 inches long. The live weight of the individual found is estimated on the basis of comparisons with extant lizards of the genus of kites to 3.95 grams.

The entire body is consistently covered with predominantly small, granular scales; Bone plates are not recognized by the fossil.

The skull, the short, round snout and rounded temple edges are possibly more signs of a youthful age of the animal. The dorsal process of the maxilla is iguana typically located far forward; it forms with the Os jugale a rectangular structure, a hallmark of all Acrodonta with the exception of chameleons. The dentition was akrodont, so the teeth sit without root on the upper edge of the jaw. These references are in Xianglong larger teeth in the rear than in the front part of the jaw. A rod-like appendage of the hyoid bone supported the large area covered with scales Kehl fold. The front of the triangular teeth are significantly smaller than the posterior teeth and have a smaller base.

For confirmation of many of these features more fossils are needed since the rounded snouts and temporal edges might reflect only a feature of the youth stage, and many sutures ( cranial sutures ) are covered by scales.

Skeleton

The front legs of the fossil are thin and only half as long as the hind legs, similar to many recent tree-dwelling reptiles. The Elle is shorter than the radius; the two bones diverge from each other significantly. The metacarpal bones are striving apart. The fourth metacarpal is the shortest. The clavicle of Xianglong was thin, rod-shaped and curved. The fibula is much thinner than the tibia. The first toe is severely bent, the strongly elongated fifth toe is spread apart, and the fifth metatarsal is provided with two hooks. The Phalangenformel (represents the number of bones in the fingers ) is 2-3-4-5-4.

On 5 to 21 of a total of 24 short, procoelous (front vaulted ) Präsakralwirbel ( vertebrae before the sacrum ) narrow, laterally elongated transverse processes are visible. Behind it are two sacral vertebrae ( sacral vertebrae ). The tail has 50 vertebrae and makes 9.5 by 15.5 centimeters, the majority of the total length of. There is no predetermined breaking point for autotomy available.

Patagium

Perhaps the most striking feature of the fossil is the almost perfectly preserved flight membrane ( patagium ), which is quite similar also present at today's genre of kites. Would spread the span of the wing membrane with the holotype be about 11.5 inches, the area of ​​the wing membrane amounts to 16.65 square centimeters.

The patagium is supported by eight highly elongated ribs, which run parallel collagen fibers were detected. The second rib is the longest and thickest. It supports the " leading edge " that the air flowing facing edge of the Patagiums, and is supported by the adjacent first rib. Remove the ribs from the following in size, thus the edge of the Patagiums tapers to the rear. The trailing edge is very thin and supported only by the collagen fibers, since the ribs already in front of this area. In the area of ​​" leading edge " can be detected large scales; the rest of the Patagiums seems to be uncovered. The wing membrane of the fossil is half open; probably due to the postmortem relaxation of the normally folded Patagiums.

Paleobiology

Unlike the majority of the Squamata ( Squamata ) Xianglong was zhaoi an arboreal. Especially long and strongly curved claws and fingers as well as the proportions between the front and hind legs are unique adaptations to climbing.

Similar to today's kites and fossil Gleitreptilien the Kuehneosauridae and Mecistotrachelos had Xianglong - developed a system based on extended ribs patagium - as the earliest known to date Schuppenkriechtier with this property. Further, comparable reptiles were Coelurosauravus whose patagium, however, was supported by rod-like bone appendages, and the prolacertiforme Sharovipteryx whose flight membranes were stretched between torso and limbs. For sliding the ribs were spread; at rest, they were applied to the body. The patagium of Xianglong is pointed as a wing on the leading edge thicker and outward, a fairly rare feature among gleitfliegenden terrestrial vertebrates. The wing membrane is reinforced naked and collagen fibers; a feature which is only known from pterodactyls and Sharovipteryx otherwise.

The surface load of the Patagiums of 0.24 grams per square centimeter is obtained from the ratio of the area to the estimated live weight of the animal. The Gleitmembran was about three times as long as wide. These relations are similar to those of fast-flying birds with good maneuverability, such as the passerines. The Miterstbeschreiber Xu Xing believes that Xianglong probably could glide about 50 to 60 meters wide, similar ranges are specified for kites.

Thalattosauria

Archosauromorpha, including Sharovipteryx ( Prolacertiformes ) and Mecistotrachelos (unstable position)

Kuehneosauridae

Maromoretta

Sphenodontia

Pleurodonta

Xianglong

Agamas, including Draco

Chameleons

More Squamata

System

Xianglong zhaoi attributable almost certainly the Schuppenkriechtieren, on the basis of characteristics such as the procoelous cervical and thoracic vertebrae, lack of Gastralrippen and the heavily modified metatarsal. It is believed that Xianglong a member of the Acrodonta ( group within the Iguania to the Agamas and the Chameleons belong ) was an uncertain position. The Acrodonta is characterized by the akrodonte dentition is also present in Xianglong. A cladistic study could confirm the assumption, the Xianglong was a member of the Acrodonta; several features of the physique with other reptiles were compared.

Flight membranes developed within the reptile several times convergently ( independently ), there is no close relationship between Xianglong and other reptiles with patagium. Although the kite also belong to Acrodonta, but the relationship ends at the family level. Xianglong probably was not the Agamas, which also contain the kites.

Swell

• Pi - Peng Li, Ke - Qin Gao, Lian- Hai Hou Xing & Xu (2007): A gliding lizard from the Early Cretaceous of China. Proceedings of the National Academy of Sciences 104 (13 ), pp. 5507-5509 ( full text, PDF, 1.5 MB).

The information in this article originate for the most part the original description, in addition, the following sources are cited: