Graciliraptor
Live reconstruction
- Liaoning, China ( Yixian Formation)
- Graciliraptor lujiatunensis
Graciliraptor was a genus of small carnivorous dinosaur from the group of Dromaeosauridae. So far, a single fragmentary skeleton is known from the Yixian Formation ( Jehol Group) of Liaoning Province and dates about 128 million years old is ( Hauterivian, Lower Cretaceous ). The only known species is Graciliraptor lujiatunensis. Graciliraptor was an early and original representatives of Dromaeosauridae, who was closely related to Sinornithosaurus and Microraptor and forms with them a designated as Microraptorinae group. From other Dromaeosauriden he differed mainly by the very slender skeleton.
Features
Graciliraptor was a small Dromaeosauridae with a length of about 1.1 meters and a weight of about 3.3 kg. In the only known copy of it was probably an adult individual, to which the partial fusion of talus ( astragalus ) and calcaneus ( calcaneus ) points. Like all Dromaeosauriden had Graciliraptor disproportionately long arms, the characteristic enlarged sickle- claw on the second toe rods and braces like the vertebrae of the tail. These braces are extremely elongated spinous processes ( postal and prezygapophyses and chevron bones). The discovery of an intact, horizontal S -shaped curved tail of Velociraptor shows that the tail despite these efforts a considerable lateral mobility exhibited in larger Dromaeosauriden. However, the tail of smaller Dromaeosauriden seems to have been fixed, after which point out the very straight tails in different Microraptor fossils. Although springs are in the fossil record at Graciliraptor, saith the detection of feathers in a variety of other Dromaeosauriden including Microraptor and Sinornithosaurus that all members of the group were feathered including Graciliraptor.
The arm bones are almost completely preserved. The Elle ( ulna ) makes 86 % of the length of the humerus from (humerus ), making it longer than other Dromaeosauriden. The radius ( radius) is 53 % of the thickness of the ulna very thin, like Microraptor, Sinornithosaurus and modern birds, but unlike most other theropods, only show small differences in the thickness of these two bones. The hand is proportionally longer than other Dromaeosauriden and makes 130 % of the length of the humerus. An original feature for example, was arctometatarsale configuration of the foot bones; so touched the second and fourth metatarsals and the third pushed backwards.
As the name implies, Graciliraptor is among the theropods grazilsten at all. Various affiliated with this very slender skeleton characteristics to distinguish this species from other genera used ( autapomorphies ): So the middle caudal vertebrae were extremely long and thin; also the tibiotarsus ( under foot ) and most of the foot bones, especially the phalanx III-1 were, relative to its maximum width very slim. Other autapomorphies include the rectangular cross section of the proximal (upper) tibia shaft and the second metatarsal ( metatarsal II), which was than all the other metatarsal bones more robust.
Fund and naming
The only known skeleton was discovered near the village Lujiatun, in the Town of Beipiao in western Liaoning. The site belongs to the lowest layer member of the Yixian Formation, a formation of the Jehol Group. The Fund ( holotype, specimen number IVPP V 13474 ) is preserved in the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and consists of a fragmentary lower jaw (maxilla ) with some teeth, almost complete right arm and the fragmentary left arm, the majority of the left lower leg ( tibiotarsus ) and of the right tibiotarsus and thigh bone (femur ), the partial left and right foot, and 10 caudal vertebrae.
The fossil was described in 2004 by Xing Xu and Wang Xiaolin first time scientifically. The name Graciliraptor (Latin gracilis - " Slim " raptor - " Robbers" ) means something like " graceful predator " and refers to the very slender legs and tail of this theropod. The species name lujiatunensis has the village Lujiatun in whose area the fossil was discovered.