Tianyuraptor

Live reconstruction of Tianyuraptor ostromi

• Liaoning (China), Yixian Formation

• Tianyuraptor ostromi

Tianyuraptor is a genus theropod dinosaur from the group of Dromaeosauridae. So far, a single, nearly complete skeleton is known, which dates from the Jehol Group in western Liaoning (China) and to the middle Cretaceous ( Barremian ) is dated.

The only way Tianyuraptor ostromi was described by Zheng and colleagues in 2009. Unlike other Dromaeosauriden Tianyuraptor has unusually short arms and a relatively small wishbone ( furcula ) on. He is regarded as a basal (original ) Dromaeosauride and could basalste the representatives of Dromaeosauriden subgroup Microraptorinae be.

Features

Tianyuraptor was a medium-sized Dromaeosauride. The only known specimen was not yet fully grown, as evidenced by the degree of fusion of different skeletal parts. Unlike many other finds from the Jehol Group missing remains of soft tissue or feathers.

The skull was large and longer than the femur ( thigh bone). The tail was about 4.8 times longer than the femur, and thus relatively long, similar to other Microraptorinen. The cervical vertebrae were about the same as the vertebrae - unlike other Microraptorinen that showed proportionally longer neck vertebrae. An important autapomorphy, that is a feature by which the species of related genera can distinguish, shows up in the middle caudal vertebrae, which were more than twice as long as the posterior dorsal vertebrae.

Tianyuraptor showed very short and thin arms, which accounted for only 53% of hindlimb length. Other Dromaeosauriden show, in contrast, very long arms, which usually accounted for over 70% of hindlimb length. Another autapomorphy, the proportion very long hind legs, which were about three times as long as the dorsal spine. The tibiotarsus (lower leg and upper foot bones ) was 135 % of the femur length ratio significantly greater than in other similarly large Dromaeosauriden.

The wishbone ( furcula ) was extremely slim and very small, so it was only a fifth of the length of the femur. The shoulder blade ( scapula ) was relatively short and robust, it was not fused with the coracoid ( coracoid ). The approximately rectangular coracoid lacked the large window that showed other Microraptorinen.

System

Tianyuraptor considered a very basal Dromaeosauride. Thus, this genus shows some features that the Unenlagiinen - were typical, but absent in the Dromaeosauriden Laurasias - basal Dromaeosauriden Gondwana. Dromaeosauriden from the Jehol Group Liaoning how Sinornithosaurus, Microraptor and Graciliraptor are summarized within the monophyletic taxon Microraptorinae. Tianyuraptor showed some synapomorphies (shared derived characteristics) of the Microraptorinen, such as significantly reduced phalanx III -2. However, many Microraptorinen - synapomorphies were missing Tianyuraptor, including the large oval window of the Croacoiden.

Tianyuraptor could thus have been the basalste Microraptorine. While in some Microraptorinen the ability to glide or even the active flight is believed to show the short arms and the small leg of Tianyuraptor that this genus was not capable of flight. If Tianyuraptor was actually an early Microraptorine, which could indicate that evolved the ability to fly the Microraptorinen independently of other groups such as the birds. However, one other idea, according Tianyuraptor could also have been no Microraptorine, but the representatives of all basalste dromaeosaurid Laurasias with the exception of Microraptorinae.

Fund and naming

The only known skeleton ( holotype, specimen number STM1 -3) was discovered in Ling Yuan in western Liaoning. Stratigraphically the Fund comes from the Lower Cretaceous Yixian Formation. The Fund is a nearly complete skeleton, probably the only the rear three vertebrae of the tail missing.

The name refers to the Tianyuraptor Tianyu Museum of Nature, which kept the fossil; raptor is Latin for " robbers ". The Artepitheth ostromi honors the paleontologist John Ostrom major who has made ​​outstanding contributions to important work on Dromaeosauriden.