Graciliraptor
| Graciliraptor | ||||||||||||
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Live reconstruction |
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Hauterivium ) | ||||||||||||
| 128 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Graciliraptor | ||||||||||||
| Xu & Wang , 2004 | ||||||||||||
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Graciliraptor was a genus of small carnivorous dinosaurs belonging to the Dromaeosauridae group . So far, a single fragmentary skeleton is known that comes from the Yixian formation ( Jehol group ) in the Chinese province of Liaoning and is about 128 million years old ( Hauterivium , Lower Cretaceous ). The only known species is Graciliraptor lujiatunensis . Graciliraptor was an early and original representative of the Dromaeosauridae, which was closely related to Sinornithosaurus and Microraptor and with these forms a group called Microraptorinae. It differed from other dromaeosaurids mainly in its very slender skeleton structure.
features
Graciliraptor was a small Dromaeosauridae with a length of about 1.1 meters and a weight of about 3.3 kg. The only known specimen was probably an adult, as indicated by the partial fusion of the talus (astragalus) and heel bone (calcaneus). Like all dromaeosaurids, Graciliraptor had proportionally long arms, the characteristic enlarged sickle claw on the second toe and rod-like struts of the caudal vertebrae. These struts are extremely elongated vertebral processes (post- and prezygapophyses as well as chevron bones ). The discovery of an intact, horizontally S-shaped curved tail of Velociraptor shows that the tail of larger dromaeosaurids exhibited considerable lateral mobility despite these struts. However, the tail of smaller dromaeosaurids seems to have been rigid, as indicated by the very straight tails in various Microraptor fossils. Although feathers in Graciliraptor are not known to be fossilized, evidence of feathers in a variety of other dromaeosaurids including Microraptor and Sinornithosaurus suggests that all members of the group including Graciliraptor were feathered.
Almost all of the arm bones have survived. The Elle (ulna) makes 86% of the length of the humerus from (humerus) and is therefore longer than for other Dromaeosauriden. The spoke (radius) is very thin at 53% of the thickness of the ulna, as in Microraptor , Sinornithosaurus and modern birds, but unlike most other theropods, which show only slight differences in the thickness of these two bones. The hand is proportionally longer than other dromaeosaurids and makes up 130% of the length of the humerus. An original feature was, for example, the approximately arctometatarsal configuration of the metatarsal bones with a triangular cross section of the lower ( distal ) part and upward ( proximad ) tapering upper part of the third (middle) metatarsal. However, in contrast to the “real” arctometatarsus, the fourth (outer) metatarsal is the slimmest of the three metatarsals.
As the name suggests, Graciliraptor is one of the most graceful theropods of all. Various features associated with this very slender skeleton structure are used to distinguish this genus from other genera ( autapomorphies ): The middle caudal vertebrae were extremely long and thin; the tibiotarsus (lower leg) and most of the bones of the foot, especially the phalanx III-1, were very slender relative to their maximum width. Further autapomorphies include the rectangular cross-section of the proximal (upper) tibia shaft and the second metatarsal bone (metatarsal II), which was significantly more robust than all other metatarsal bones.
Find and naming
The only known skeleton was found near Lujiatun Village, in the Beipiao City area of western Liaoning. The site belongs to the lowest layer of the Yixian formation , a formation of the Jehol group . The find ( holotype , copy number IVPP V 13474) is kept in the Institute for Vertebrate Paleontology and Paleoanthropology in Beijing and consists of a fragmentary lower jaw (maxilla) with some teeth, the almost complete right arm and the fragmentary left arm, most of the left lower leg ( Tibiotarsus) as well as the right tibiotarsus and thigh bone (femur), the partial left and right foot, as well as 10 caudal vertebrae.
The fossil was first scientifically described in 2004 by Xing Xu and Xiaolin Wang . The name Graciliraptor ( Latin gracilis - "slim", raptor - "predator") means something like "graceful predator" and refers to the very slender legs and tail of this theropod. The species name lujiatunensis refers to the village of Lujiatun, in the vicinity of which the fossil was discovered.
supporting documents
literature
- Xing Xu , Xiao-Lin Wang: A New Dromaeosaur (Dinosauria: Theropoda) from the Early Cretaceous Yixian Formation of Western Liaoning. In: Vertebrata PalAsiatica. Vol. 42, No. 2, pp. 111-119, (PDF; 294 kB) .
Individual evidence
- ^ Graciliraptor. In: The Paleobiology Database. Retrieved May 11, 2010 .
- ^ Alan H. Turner, Diego Pol, Julia A. Clarke, Gregory M. Erickson, Mark A. Norell : A Basal Dromaeosaurid and Size Evolution Preceding Avian Flight. In: Science . Vol. 317, No. 5843, 2007, pp. 1378-1381, doi : 10.1126 / science.1144066 , digitized version (PDF; 507.41 kB) , Supporting Online Material (PDF; 755.11 kB) .
- ^ Mark A. Norell, Peter J. Makovicky : Important features of the dromaeosaurid skeleton. 2, Information from newly collected specimens of Velociraptor mongoliensis (= American Museum Novitates. No. 3282, ISSN 0003-0082 ). American Museum of Natural History, New York NY 1999, online .
- ↑ Sunny H. Hwang, Mark A. Norell, Ji Qiang, Gao Kequin: New specimens of Microraptor zhaoianus (Theropoda: Dromaeosauridae) from northeastern China (= American Museum Novitates. No. 3381). American Museum of Natural History, New York NY 2002, online .
- ^ Alan H. Turner, Peter J. Makovicky, Mark A. Norell: Feather Quill Knobs in the Dinosaur Velociraptor. In: Science. Vol. 317, No. 5845, 2007, p. 1721, doi : 10.1126 / science.1145076 .
- ↑ Xing Xu: Deinonychosaurian Fossils from the Jehol Group of Western Liaoning and the Coelurosaurian Evolution. Chinese Academy of Sciences, Beijing 2002 (dissertation).