Sinornithosaurus

*Sinornithosaurus millenii*

* Timothy Bradley Artwork
* Robert F Walters Artwork

***Sinornithosaurus*** (derived from a combination of Latin and Greek, meaning 'Chinese bird-lizard') is a genus of feathered dromaeosaurid dinosaur from the Lower Cretaceous Period (Middle Barremian) of the Yixian Formation in what is now China. It caused a sensation because it was the fifth of the non - avian feathered dinosaur genera discovered by 1999. It was collected from the Sihetun locality of western Liaoning. It was in Layer 6, lower (Chaomidianzi) Yixian Formation, Jehol Group.

The holotype specimen is **IVPP V12811**, in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China. Another specimen, **NGMC - 91**, is probably a juvenile *Sinornithosaurus*. Qiang et al. (2001) were reluctant to name **NGMC - 91** because, although the specimen is completely articulated, almost all of the bones shattered when the fossil slabs were split, so that only the silhouettes of theses bones are clear in most of the part and counterpart. This obscured diagnostic skeletal features, which made the specimen's genus uncertain. **NGMC - 91**, also called **"Dave"**, is in the collection of the National Geological Museum of China. It was collected in Fanzhangzi quarry, near Lingyuan City, Liaoning Province, China. This is around 130km from the Sihetun locality. A specimen of the fish *Lycoptera* is also preserved near the foot of **NGMC - 91**.

Xu Xing described *Sinornithosaurus* and performed a phylogenetic analysis which demonstrates that it is basal, or primitive, among the dromaeosaurs. He has also demonstrated that features of the skull and shoulder are very similar to *Archaeopteryx* and other Avialae. Together these two facts demonstrate that the earliest dromaeosaurs were more like birds than the later dromaeosaurs were. This contradicts one argument made by critics of the theory that birds evolved from dinosaurs. See Temporal paradox (paleontology).

## Description

It was the fifth non–avian feathered dinosaur genus discovered by 1999. The original specimen was collected from the Sihetun locality of western Liaoning. It was found in the Jianshangou beds of the Yixian Formation, dated to 124.5 million years ago. Additional specimens have been found in the younger Dawangzhangzi bed, dating to around 122 million years ago. Xu Xing described *Sinornithosaurus* and performed a phylogenetic analysis which demonstrated that it is basal, or primitive, among the dromaeosaurs.
Specimens of Sinornithosaurus have preserved impressions of feathers both covering the entirety of the body and forming the wings. These feathers were indistinguishable in form from those found on birds from the same geological deposits. The body (contour) feathers were generally between 3–4.5 cm long and included two types: the first type are formed of several filaments joined into "tufts", similar to modern down feathers. The second type, including those on the arms, were composed of rows of filaments (barbs) joined along a main shaft (rachis), making them similar in structure to modern bird feathers.

However, unlike the wing feathers of flying birds, they did not have the secondary branches with tiny little hooks (barbules) that flight feathers have, which allow the flight feathers to form a continuous vane. Some scientists have suggested that the feathers might have allowed Sinornithosaurus to glide for short distances after leaping from trees.  A 2010 study indicated that Sinornithosaurus may have had feathers which varied in color significantly across different regions of the body, based on analysis of microscopic cell structures in preserved fossils.

Some paleontologists have hypothesized that Sinornithosaurus millenii had venom due to some dentitional similarities to modern venomous snakes. Lately; the possibility that this dinosaur species could be venomous is highly debated.

## Feathers

Both of the *Sinornithosaurus* specimens above preserved impressions of feathers. They were composed of filaments, and showed two features that indicate they are early feathers. First, several filaments were joined together into "tufts", similar to the way down is structured. Second, a row of filaments (*barbs*) were joined together to a main shaft (*rachis*), making them similar in structure to normal bird feathers. However, they do not have the secondary branching and tiny little hooks (*barbules*) that modern feathers have, which allow the feathers of modern birds to form a discrete vane. In NGMC - 91 the feathers covered the entire body, including the head in front of the eye, the neck, wing - like sprays on the arms, long feathers on the thighs, and a lozenge - shaped fan on the tail like that of *Archaeopteryx*.

## Classification

*Sinornithosaurus* was a member of the family Dromaeosauridae, a group of agile, predatory dinosaurs with a distinctive sickle-shaped toe claw, which also includes *Deinonychus* and *Utahraptor*. It lived about 125 million years ago in the Barremian age of the Lower Cretaceous period, which makes it among the earliest and most primitive dromaeosaurids yet discovered. The presence of vaned feathers on *Sinornithosaurus* is consistent with feather evidence from other Dromaeosaurs. see *Microraptor*, *Velociraptor*, and *Rahonavis*. see also feathered dinosaurs.

*Sinornithosaurus* is known from at least two species. *S. millenii* ("millennium Chinese bird-lizard") is the type species, described in 1999. A second species, *S. haoiana* ("Hao's Chinese bird-lizard") was described by Liu *et al.* in 2004 based on a new specimen which differed from *S. millenii* in features of the skull and hips. An incredibly well-preserved microraptorian nicknamed "Dave" (specimen NGMC 91) may represent a third species of *Sinornithosaurus*, or a juvenile.

## Discovery

*Sinornithosaurus* was discovered by Xu Xing, Wang Xiaolin and Wu Xiaochun of the Institute of Vertebrate Paleontology and Paleoanthropology of Beijing. An almost-complete fossil with feather impressions, was recovered from Liaoning Province, China, in the Yixian Formation; the same incredibly rich location where four dinosaurs with feathers were discovered previously, *Protarchaeopteryx*, *Sinosauropteryx*, *Caudipteryx*, and *Beipiaosaurus*.

## JPInstitute.com Description

Sinornithosaurus was a feathered raptor that lived in China. This is a very important fossil because it clearly shows the feathers on this member of the family that includes Velociraptor and Dromaeosaurus. It was a small, quick, and agile hunter that probably ate small dinosaurs, lizards, and reptiles. It did not have wings and its feathers were probably used for keeping it warm, for showing off, or to help identify it to its friends.

Sinornithosaurus shows a number of very bird-like features; its shoulder is designed so that it can be moved in the same way that a bird flaps its wings and a number of pelvic features are similar to those found in birds. The feather-like filaments seem to cover the entire body of the animal. Since this is a basal member of the dromaeosauridae, it has caused a re-evaluation of the evolutionary process of later dromaeosaurids.

## Dinosaur Field Guide Description

Sinornithosaurus ( "Chinese bird lizard") is one of the oldest known dromaeosaurs, or raptors. This was an early relative of Velociraptor and Deinonychus. Like Velociraptor, it was a fairly small dinosaur, but it was probably very dangerous. It had sharp, curved teeth in its jaws, long grasping hands at the end of long arms, and a killer sickle claw on the second toe of each foot. What makes Sinornithosaurus more famous, though, is that fact that it was "fuzzy"! All over the body of Sinornithosaurus were long filaments. These structures were protofeathers, a fuzzy body covering that eventually evolved into true feathers. Both protofeathers and true feathers are "soft" features that do not fossilize easily. But the fine grained mud of the Yixian Formation. where Sinornithosaurus was found, was able to preserve the soft features of the dinosaurs, other animals, and plants that died there. Other theropods found in the Yixian Formation include Beipiaosaurus, Caudipteryx, Confuciusornis, and Sinosauropteryx. They all were found to have either protofeathers or true feathers. Before these finds, scientists thought that raptor dinosaurs like Deinonychus and Velociraptor were covered only in scales. This is because the rocks where they were found did not preserve their soft body coverings. Now, with the discovery of Sinornithosaurus and the other theropods found in the Yixian), we know that raptors and all the other advanced, bird-like
meat-eating dinosaurs were covered with either fuzzy protofeathers or true feathers.

### Fun Facts

A raptor from Montana that was very similar in size to Sinornithosaurus was named Bambiraptor because its long legs reminded the discovery of the fictional deer Bambi.

### Trivia

The first detailed study of the body covering of Sinornithosaurus was
published in March 2001. It showed that much of this little dinosaur was covered by down, like the fluff on the body of baby chicks. Some of this dinosaur's protofeathers, however were longer shafts with branches coming off of them, like the feathers of modern adult birds.

## Links

http://web.archive.org/web/20040214163933fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_sinor.html#

## References

1. ↑ Swisher, Carl C., Wang, Yuan-qing, Wang, Xiao-lin, Xu, Xing, Wang, Yuan. (1999). "Cretaceous age for the feathered dinosaurs of Liaoning, China". *Nature* 400:58-61 1 July 1999.
2. ↑ 2.0 2.1 Qiang, Ji, Norell, Mark A., Gao, Ke-Qin, Ji, Shu-An, Ren, Dong. (2001) "The distribution of integumentary structures in a feathered dinosaur" "Nature" 410:1084-1087 26 April 2001.
3. ↑ Xu, Xing, Wang, Xiao-Lin, Wu, Xiao-Chun. (1999) "A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China" "Nature" 401:262-266 16 September 1999.
4. ↑ Xu, Xing, Wu, Xiao-Chun. (2001). "Cranial morphology of *Sinornithosaurus millenii* Xu *et al.* 1999 (Dinosauria:Theropoda:Dromaeosauridae) from the Yixian Formation of Liaoning, China". *Canadian Journal of Earth Sciences* 38:1739-1752 (2001)