Sinornithosaurus

Sinornithosaurus millenii in Hong Kong Science Museum

• Liaoning (China), Yixian Formation

Sinornithosaurus is a genus theropod dinosaur from the group of Dromaeosauridae. Findings of this animal come from the Yixian Formation ( Lower Cretaceous ) from the Chinese province of Liaoning. Sinornithosaurus was a very bird -like feathered dromaeosaurid, who distinguished himself by the proportionally longest arms of all theropods. According to a recent study suggests that animal hunted its prey probably with poison. This early and basal ( original ) Dromaeosauride applies mostly as a representative of Dromaeosauriden subgroup Microraptorinae. At least two previously known skeletons, which are attributed to two types, and Sinornithosaurus millenii Sinornithosaurus haoiana. Another skeleton, nicknamed "Dave" may also belong to this genus.

Features

Sinornithosaurus was a small Dromaeosauride. The type specimen was estimated to 128 cm long and 5 kg in weight, with the skull about 15.2 cm and the femur ( thigh bone) was about 14.8 cm long.

The skull of the type specimen is nearly complete, although most of the bones of the discovery no longer in anatomical network. As with all Dromaeosauriden the skull was slightly built and showed a large skull and a narrow snout. The snout was about 7.5 cm long and proportionally shorter than in Velociraptor and Deinonychus. The arms were the longest in the ratio of all non-avian theropods, and are estimated at 80 % of hindlimb length. The metatarsals showed a arctometatarsale position: So touched the second and fourth metatarsals and the third pushed back so this was visible from the front, only in the lower part of the midfoot. This feature can be found at Dromaeosauriden otherwise only in Microraptor.

Autapomorphies, ie qualities enabling the species of other genera can distinguish, can be found in various parts of the skeleton: The antorbitale fossa ( fossa ) in front of the large eye sockets was great as with other Dromaeosauriden, but showed, in contrast to other genera in the front area a number of similar ornament pits and hills. The coracoid ( coracoid ) shows a window which, however, was now also detected in Microraptor. Other diagnostic features include, among others, the large breastbone ( sternum) with a.

In particular, the shoulder girdle showed strong similarities to the earlier birds and supports the theory that the Dromaeosauridae was more closely related to birds than any other known dinosaur groups. For example, was the wishbone ( furcula ) boomerang shaped similarly, similar to Archaeopteryx, but unlike for example in Velociraptor. Other very bird-like features can be found in the pelvis and hind leg region.

Springs and possible toxic bite

The type specimen of Sinornithosaurus millenii shows 30 to 45 mm long and 1-3 mm wide filament structures that are interpreted as springs. The discovery shows both wispy feathers in the filaments converge at a point, as well as filaments that run along a central stem. The possible Sinornithosaurus fund NGMC 91 ( "Dave" ) shows feathers all over the body, with the exception of the lower portions of the legs.

A recent study by Gong and colleagues ( 2009) discovered in the type specimen of Sinornithosaurus millenii evidence of a poisonous bite: Sun, showing the skeleton next to an unusual dentition notched teeth, a cavity, which represented probably a poison gland, as well as a channel of this poison gland led to the tooth base. These features are analogous to today's poisonous lizards. The researchers suggest that Sinornithosaurus and related Dromaeosauriden hunting could have made on birds.

Another team of scientists led by Federico Gianechini published a study in 2010, which raises doubts as to the toxicity of Sinornithosaurus. They showed that notches in the teeth are by no means unique in this genus, but also in many other theropods occur, especially with other representatives of the Dromaeosauridae. Furthermore, they noticed that the teeth are not, as alleged by Gong and his team were exceptionally long, but had merely slipped out of the tooth sockets, an artifact that occurs frequently flattened fossils at. Ultimately, they could the presence of a chamber for poison glands, such as Gong and his team it postulated not verify.

In the same issue of the journal Gong and colleagues responded to the criticism. They admitted that ridged teeth were quite common among theropods (although they remarked that in they were probably widespread only in the feathered Maniraptora ). They then hypothesized that poison a primitive feature of all Archosauria, if not could have been even all reptiles, which had been preserved only in a few lines of development. They also resisted the statement that the teeth in the holotype of Sinornithosaurus had been driven far from the jaw, while admitting that the teeth are not in their natural position. Gong continued to claim that some undescribed specimens, whose teeth are preserved in association with the jaw, show the same tooth length.

Discoveries and naming

The first Fund ( holotype, IVPP copy number ) comes from Sihetun, a famous locality for fossil fish, birds and dinosaurs in western Liaoning. Stratigraphically, the skeleton comes from the layer 6 of the lower Yixian Formation of the Jehol Group. 1999, the Fund by Xu, Wang and Wu Sinornithosaurus as described millenii scientifically. Sinornithosaurus ( gr sinai, lat Sinae - " Chinese"; ornis gr - " bird"; sauros gr - " lizard" ) means something like " bird Similar dinosaurs from China " while the Artepitheth millenii (Latin Millennium ) points to the discovery of this animal just before the turn of the millennium.

A second type, Sinornithosaurus haoiana ( " Hao 's Sinornithosaurus " ), was described by Liu and colleagues in 2004. It is based on a new skeleton that differences Sinornithosaurus millenii in the skull and pelvis shows.

A further möglicherer Sinornithosaurus - Fund ( copy number NGMC 91) was described in 2001 by Qiang and colleagues and is nicknamed "Dave". The find was discovered in the quarry Fanzhangzi, 20 km south-west of Ling yuan in Liaoning. This skeleton is complete and handed in the anatomical network on two stone plates, the first stone slab shows the bone and the second specimens of the bone. When disassembling the column outlet plate when collecting fossils, however, most of the very brittle bones are broken, which is why many anatomical details can not be adequately investigated. "Dave" shows some differences to Sinornithosaurus, such as an unusually bent first metatarsal bone - however, these differences could be attributed in part to individuals of different ages. Near the left foot of the skeleton is a fossil of the small fish Lycoptera.