Xianglong (genus)
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Live reconstruction from Xianglong |
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| Xianglong | ||||||||||||
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Xianglong was one of the iguanas (Iguania) counting genus of the scalloped reptiles from the lower Cretaceous of China. The only known species is Xianglong zhaoi . It is similar to the recent kites ( Draco ), with which Xianglong is not closely related. The first description was made by Li Pipeng et al. in 2007. So far, the holotype (copy number LPM 000666) is the only known fossil from Xianglong . It is visible on a main and a counter plate and is complete and well preserved. It is kept in the Liaoning Paleontological Museum.
With a plane spanned by extended ribs patagium the reptile possessed the ability to glide . The generic name Xianglong comes from Chinese and means something like "flying dragon", the specific epithet zhaoi honors Zhao Dayu, one of the founders of the Paleontological Museum in Liaoning.
Geological background
 
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Locality of Xianglong zhaoi in China |
The fossil was discovered in the Zhuanchengzi layer near Zhuangchengzi Village, near Yizhou Township in Liaoning Province , China . The Zhuanchengzi layer is dated to 122 to 120 million years, sometimes 145 to 140 million years. The Zhuangchengzi layer belongs to the Yixian Formation , a formation of the Jehol group . It consists largely of siliciclastic sedimentary rocks that were deposited in lakes. Individual layers of tuff and basalt can be traced back to volcanic activity. The Yixian Formation is famous for its extraordinary fossil conservation, especially for the transmission of soft tissue structures (near Xianglong, the flight membrane), which is why it and the Jehol group as a whole are referred to as a conservatory . Particularly the numerous discoveries of feathered dinosaurs such as Sinosauropteryx and early birds as Confuciusornis have in the past twenty years to a sudden increase of knowledge about the evolutionary history of birds in the Mesozoic out.
The climate at the time of the deposition was probably characterized by an alternation of warm, humid rainy seasons and dry seasons. Away from the lake areas, the climate was generally drier. Conifers dominated the vegetation; furthermore, ferns , horsetail , bear moss and rarely early flowering plants occurred. The good preservation of the Yixian fossils can be explained by their rapid embedding: dead animals sank to the bottom of a lake without long transport through rivers and were covered by fine-grained sediment. Land animals like Xianglong have been preserved in the same way as lake dwellers and are found in the same strata. Most of the best preserved fossils are found directly under the volcanic layers, as these rapidly solidified deposits effectively cut off underlying layers from oxygen, preventing decomposition by other organisms and putrefaction .
anatomy
The information on the morphology of this gliding reptile is based on the holotype (specimen number LPM 000666), the only known fossil of Xianglong zhaoi . The specimen was probably not yet fully grown, which can be determined by the only slightly ossified tarsal bones and the lack of ossified carpal bones .
The fossil found is 15.5 centimeters long. The live weight of the found individual is estimated based on comparisons with recent lizards of the kite genus at 3.95 grams.
The entire body is covered with mostly small, granular scales; Bone plates are not recognizable on the fossil.
skull
The short, round snout and the rounded temple edges on the skull are possibly further signs of the animal's youthful age. As is typical for iguanas, the dorsal process of the upper jaw is located far forward; it forms a rectangular structure with the os jugale , a characteristic of all acrodonts with the exception of chameleons . The teeth were acrodontic , so the teeth sit on the upper edge of the jaw without a tooth root. Indications of this in Xianglong are larger teeth in the back than in the front part of the jaw. A rod-like extension of the hyoid bone supported the large, scale-covered throat fold. The front of the triangular teeth are significantly smaller than the rear teeth and have a smaller base.
Further fossils are necessary to confirm many of these features, as the rounded edges of the snout and temples may only represent a feature of the youth stage, and many sutures (skull sutures) are covered by scales.
skeleton
The forelegs of the fossil are thin and only half the length of the hind legs, similar to that of numerous recent tree-dwelling reptiles. The cubit is shorter than the spoke ; the two bones diverge clearly from one another. The metacarpal bones also strive away from each other. The fourth metacarpal is the shortest. The clavicle of Xianglong was thin, rod-shaped and bent. The fibula is much thinner than the shin . The first toe is strongly curved, the greatly elongated fifth toe is splayed out, and the fifth metatarsal is provided with two hooks. The phalangeal formula (represents the number of bones in your fingers) is 2-3-4-5-4.
On the 5th to the 21st of the total of 24 short, procoelic (front arched) presacral vertebrae (vertebrae in front of the sacrum ), narrow, laterally elongated transverse processes can be seen . Behind it there are two sacral vertebrae (sacral vertebrae). The tail has 50 vertebrae and makes up the majority of the total length with 9.5 by 15.5 centimeters. There is no predetermined breaking point for autotomy .
Flying skin
Perhaps the most striking feature of the fossil is the almost perfectly preserved flight membrane (patagium), which is very similar to the current genus of kites. Spread out, the span of the flight skin in the holotype would have been about 11.5 centimeters, the area of the flight skin is 16.65 square centimeters.
The patagium is supported by eight greatly elongated ribs, to which collagen fibers have been found to run parallel . The second rib is the longest and thickest. It supports the " wing nose ", the edge of the patagium facing the incoming air, and is supported by the adjacent first rib. The subsequent ribs decrease in size, so the edge of the patagium tapers backwards. The rear edge is very thin and only supported by the collagen fibers as the ribs already end in front of this area. Large scales can be detected in the area of the “wing nose”; the rest of the patagium appears to be uncovered. The fossil's skin is half open; likely due to post-mortem loosening of the normally folded patagium.
Paleobiology
Unlike the majority of Squamata (Squamata) was Xianglong zhaoi an arboreal. Especially long and strongly curved claws and fingers as well as the proportions between the front and rear legs are clear adaptations to climbing.
Similar to today's kites and the fossil gliding reptiles of the Kuehneosauridae and Mecistotrachelos , Xianglong - as the earliest known scale reptile with this property - developed a patagium supported by elongated ribs. Other, comparable reptiles were Coelurosauravus , whose patagium was supported by rod-like bone processes, and the prolacertiform Sharovipteryx , whose flight membranes were stretched between the torso and limbs. The ribs were spread out for sliding; at rest they were attached to the body. The patagium of XiangLong is as wing thicker tapered at the leading edge and to the outside, a fairly rare feature under gleitfliegenden terrestrial vertebrates . The flight skin is bare and reinforced with collagen fibers; a characteristic that is otherwise only known from pterosaurs and Sharovipteryx .
The surface loading of the patagium of 0.24 grams per square centimeter results from the ratio of the surface to the estimated live weight of the animal. The sliding membrane was about three times as long as it was wide. These relationships are similar to those of fast-flying birds with good maneuverability, such as: B. the passerine birds . The co-author Xu Xing thinks that Xianglong could probably glide about 50 to 60 meters, similar distances are also given for kites.
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Tribal historical positions of sliding reptiles
according to Li et al. (2007), Fraser et al. (2007) and Mikkos Phylogeny Archive
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Systematics
Xianglong zhaoi can almost certainly be assigned to the scaled crawfish based on features such as the cervical and thoracic vertebrae, the absence of gastric ribs and the heavily modified metatarsal bone. It is believed that Xianglong was a member of the Acrodonta (group within the Iguania to which the agamas and chameleons belong), with an insecure position. The acrodonta is characterized by the acrodontic teeth that are also present in Xianglong . A cladistic investigation confirmed the assumption that Xianglong was a member of the Acrodonta; a number of physique features have been compared to other reptiles.
Flight membranes developed convergent several times within the reptiles (independently of each other), there is no closer relationship between Xianglong and other reptiles with patagium. The kites also belong to the acrodonta, but the relationship ends at the family level . Xianglong was probably not one of the agamas, which also contain 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).
Most of the information in this article comes from the first description; the following sources are also cited:
- ↑ Zhu Rixiang, Shao Ji'an, Pan Yongxin, Shi Ruiping, Shi Guanghai & Li Daming (2002): Paleomagnetic data from Early Cretaceous volcanic rocks of West Liaoning: Evidence for intracontinental rotation . Chinese Science Bulletin 47 (21), pp. 1832-1837.
- ^ Li Wen-ben (2010): Palynological assemblage from the Zhuangchengzi beds of Yixian formation in Jinjiagou, Yixian . Acta Geologica Sinica
- ↑ a b c Zonghe Zhou, Paul M. Barrett & Jason Hilton (2003): An exceptionally preserved Lower Cretaceous ecosystem . Nature 421, pp. 807-814 ( full text ; PDF; 822 kB).
- ^ Paul M. Barrett & Jason M. Hilton (2006): The Jehol Biota (Lower Cretaceous, China): new discoveries and future prospects . Integrative Zoology 1 (1), pp. 15-17 ( full text )
- ^ A b Pi-Peng Li, Ke-Qin Gao, Lian-Hai Hou & Xing Xu: A gliding lizard from the Early Cretaceous of China Supporting Information. Retrieved November 19, 2010 (additional online material for the initial description).
- ↑ a b Ker Than: Ancient Lizard Glided on Stretched Ribs. foxnews.com, March 21, 2007, archived from the original on October 16, 2012 ; Retrieved November 19, 2010 (online news).
- ^ NC Fraser, PE Olsen, AC Dooley & TR Ryan (2007): A new gliding tetrapod (Diapsida:? Archosauromorpha) from the Upper Triassic (Carnian) of Virginia . Journal of Vertebrate Paleontology 27 (2), pp. 261-265
- ↑ E. Frey, H.-D. Sues & W. Munk (1997): Gliding Mechanism in the Late Permian Reptile Coelurosauravus. Science 275, pp. 1450-1452.
- ↑ GJ Dyke, R. L. Nudds, J. M. V. Rayner (2006): Flight of Sharovipteryx mirabilis: the world's first delta-winged glider . In: Journal of Evolutionary Biology . 19 (4), pp. 1040-1043 ( full text ( memento of March 12, 2016 in the Internet Archive ).
- ↑ Wilfried Westheide & Reinhard Rieger: Special Zoology. Part 2: vertebrates or skulls. Spektrum Akademischer Verlag, Munich 2004, p. 369. ISBN 3-8274-0900-4
- ↑ Mikko Haaramo: Sauria. In: Mikko's Phylogeny Archive. Retrieved November 30, 2010 .
