Sinosauropteryx

***Sinosauropteryx*** was a cat-sized theropod dinosaur that lived in the Yixian Formation of China. It was the first non-avialan dinosaur to be discovered with evidence of feathers, (which were more like mammalian fur or a living stuffed animal rather than feathers of modern birds) and the first dinosaur for which color was partially determined. This was achieved by examining shapes of preserved melanosomes on one of the dinosaur's fossils, and it was revealed that *Sinosauropteryx* appeared to be russet-colored, with white stripes on the tail. Otherwise, *Sinosauropteryx* appears to be a typical theropod dinosaur, with shore forearms and a long tail.

Traces of color cells in the fossils of this small hunter show that its tail had a pattern of light and dark bands.

## Description

Sinosauropteryx was a small bipedal theropod, noted for its short arms, large first finger (thumbs), and long tail. The taxon includes some of the smallest known adult non-avian theropod specimens, with the holotype specimen measuring only 68 cm (27 in) in length, including the tail. However, this individual was relatively young. The longest known specimen reaches up to 1.07 m (3.5 ft) in length, with an estimated weight of 0.55 kg (1.2 lb).

Sinosauropteryx was anatomically similar to Compsognathus, differing from its European relatives in its proportions. The skull of Sinosauropteryx was 15% longer than its thigh bones, unlike in Compsognathus, where the skull and thigh bones are approximately equivalent in length. The arms of Sinosauropteryx (humerus and radius) were only 30% the length of its legs (thigh bone and shin), compared to 40% in Compsognathus. Additionally, Sinosauropteryx had several features unique among all other theropods. It had 64 vertebrae in its tail. This high number made its tail the longest relative to body length of any theropod. Its hands were long compared to its arms, about 84% to 91% of the length of the rest of the arm (humerus and radius), and half the length of the foot. The first and second digits were about the same length, with a large claw on the first digit. The first fingers were large, being both longer and thicker than either of the bones of the forearm. The teeth differed slightly (they were heterodont) based on position: those near the tips of the upper jaws (on the premaxillae) were slender and lacked serrations, while those behind them (on the maxillae) were serrated and laterally compressed. The teeth of the lower jaws were similarly differentiated.

A pigmented area in the abdomen of the holotype has been suggested as possible traces of organs, and was interpreted as the liver by John Ruben and colleagues, which they described as part of a crocodilian-like "hepatic piston" respiratory system. A later study, while agreeing that the pigmented area represented something originally inside the body, found no defined structure and noted that any organs would have been distorted by the processes that flattened the skeleton into an essentially two-dimensional form. Dark pigment is also present in the eye region of the holotype and another specimen.

## Discovery

The first fossil specimen of the dinosaur later named **Sinosauropteryx** prima was uncovered at China in August 1996 by Li Yumin. Yumin was a farmer and part-time fossil hunter who often prospected around Liaoning Province to acquire fossils to sell to individuals and museums. Yumin recognized the unique quality of the specimen, which was separated into two slabs, and sold the slabs to two separate museums in China: the National Geological Museum in Beijing, and the Nanjing Institute of Geology and Paleontology. The director of the Beijing museum, Ji Qiang, recognized the importance of the find, as did visiting Canadian palaeontologist Phil Currie and artist Michael Skrepnick, who became aware of the fossil by chance as they explored the Beijing museum's collections after leading a fossil tour of the area during the first week of October, 1996. Currie recognized the significance of the fossil immediately. As The New York Times quoted him, "When I saw this slab of siltstone mixed with volcanic ash in which the creature is embedded, I was bowled over." When originally described, the authors named Sinosauropteryx, meaning "Chinese Reptilian Wing.

## Classification

Despite its feathers, most palaeontologists do not consider Sinosauropteryx to be a bird. Phylogenetically, the genus is only distantly related to the clade Aves, usually defined as Archaeopteryx lithographica plus modern birds. The scientists who described Sinosauropteryx, however, used a character-based, or apomorphic, definition of the Class Aves, in which any animal with feathers is considered to be a bird. They argued that the filamentous plumes of Sinosauropteryx represent true feathers with a rachis and barbs, and thus that Sinosauropteryx should be considered a true bird. They classified the genus as belonging to a new biological order, Sinosauropterygiformes, family Sinosauropterygidae, within the subclass Sauriurae. These proposals have not been accepted, and Sinosauropteryx is generally classified in the family of Compsognathidae, a group of small-bodied long-tailed Coelurosaurian theropods known from the Late Jurassic and Early Cretaceous of Asia, Europe, and South America.

Below is a cladogram showing the placement of Sinosauropteryx within Coelurosauria by Senter et al. in 2012.

## Headline text

aail. In a later paper, Ji, Ji and colleagues changed their opinion and suggested GMV 2124 is probably a new taxon. In 2007, Gishlick and Gauthier supported their conclusion and tentatively re-classified this specimen as *Sinosauropteryx? sp.*, though it may belong in a new genus.

*Sinosauropteryx* is important because it had feather-like structures, yet was not very closely related to the previous "first bird" *Archaeopteryx*. There are many dinosaur families that were more closely related to *Archaeopteryx* than *Sinosauropteryx* was, including the deinonychosaurians, the oviraptorosaurians, and the therizinosauroids. This indicates that feathers may have been a characteristic of many theropod dinosaurs, not just the obviously bird-like ones, making it possible that equally distant animals such as *Ornitholestes*, *Coelurus*, and *Compsognathus* had feathers as well, although their close proximity to the origin of feathers and the presence of scales on *Juravenator* and *Tyrannosaurus* make the distribution of feathers in primitive coelurosaurs extremely difficult to estimate accurately.

Most paleontologists do not consider *Sinosauropteryx* to be a bird, because phylogenetically, it lies far from the *clade* Aves, usually defined as *Archaeopteryx* + modern birds. The scientists who discovered and described *Sinosauropteryx*, however, used a character-based (apomorphy) definition of the Class Aves, that is, any animal with feathers is a bird. They argued that the filamentous plumes of *Sinosauropteryx* represent true feathers with a rachis and barbs, and therefore that *Sinosauropteryx* should be considered a true bird. They classified it as belonging to a new biological order, **Sinosauropterygiformes**, family **Sinosauropterygidae**, within the subclass Sauriurae.

## Paleobiology

### Diet

The specimen **NIGP 127587** was preserved with the remains of a lizard (complete with skull) in its stomach, indicating that small, fast-moving animals made up part of the diet of *Sinosauropteryx prima*. Numerous lizards of this type had previously been found in the same rocks as *Sinosauropteryx* but have yet to be described.

Another possible *Sinosauropteryx* specimen, GMV 2124 (*Sinosauropteryx? sp.*), was found with three mammal jaws in its stomach region. Hurum, Luo & Kielan-Jaworowska identified two of these jaws as belonging to *Zhangheotherium* and the third to *Sinobaatar*, showing that these two mammals were part of the animal's diet. Interestingly, *Zhangheotherium* is known to have had a venom-secreting spur, like the modern platypus, showing that they fed on possibly venomous mammals.

### Reproduction

In the same specimen of *S. prima* that preserved the complete stomach contents including a lizard (NIGP 127587), several small eggs were also discovered in the abdomen. Two eggs were preserved just in front of and above the pubic boot, and several more may lie underneath them on the slab. It is unlikely that these were eaten by the animal, as they were in the wrong part of the body cavity for the egg shells to have remained intact. It is more likely that these are unlaid eggs produced by the animal itself.

Each egg measured 36 millimeters (1.4 inch) long by 26 mm (1 in) wide. The total length of this individual was 1.07 m (3.5 ft).

### Feathers

All specimens of *Sinosauropteryx* preserve integumentary structures (filaments arising from the skin) which most paleontologists interpret as very primitive feathers. These short, down-like filaments are preserved all along the back half of the skull, arms, neck, back, and top and bottom of the tail. Additional patches of feathers have been identified on the sides of the body, and paleontologist Chen, Dong and Zheng proposed that the density of the feathers on the back and the randomness of the patches elsewhere on the body indicated the animals would have been fully feathered in life, with the ventral feathers having been removed by decomposition.

The filaments are preserved with a gap between the bones, which several authors have noted corresponds closely to the expected amount of skin and muscle tissue that would have been present in life. The feathers adhere close to the bone on the skull and end of the tail, where little to no muscle was present, and the gap increases over the back vertebrae, where more musculature would be expected, indicating that the filaments were external to the skin and do not correspond with sub-cutaneous structures.

The random positioning of the filaments and often "wavy" lines of preservation indicate that they were soft and pliable in life. Examination with microscopes shows that each individual filament appears dark along the edges and light internally, suggesting that they were hollow, like modern feathers. Compared to modern mammals the filaments were quite coarse, with each individual strand much larger and thicker than the corresponding hairs of similarly sized mammals.

The length of the filaments varied across the body. They were shortest just in front of the eyes, with a length of 13 mm. Going further down the body, the filaments rapidly increase in length until reaching 35 mm long over the shoulder blades. The length remains uniform over the back, until beyond the hips, when the filaments lengthen again and reach their maximum length midway down the tail at 40 mm. The filaments on the underside of the tail are shorter overall and decrease in length more rapidly than those on the dorsal surface. By the 25th tail vertebrae, the filaments on the underside reach a length of only 35 mm. The longest feathers present on the forearm measured 14 mm.

Though the feathers are too dense to isolate a single structure for examination, several studies have suggested that the presence of two distinct types of filament (thick and thin) interspersed with each other, the tendancy for the thick filaments to appear 'stiffer' than thin filaments, and the tendancy of thin fillaments to lie parallel to each other but at angles to nearby thick filaments, suggests that the individual feathers consisted of a central quill (*rachis*) with thinner *barbs* branching off from it, similar to but more primitive in structure than modern bird feathers. Overall, the filaments most closely resemble the "plumules" or down-like feathers of some modern birds, with a thick central quill and long, thin barbs. The same structures are seen in other fossils from the Yixian Formation, including *Confuciusornis*.

#### Coloration

The fossils of *Sinosauropteryx* have shown an alternation of lighter and darker bands preserved on the tail, which may give an indication of what the animal looked like in life. Chen and colleagues initially interpreted this banding pattern as an artifact of the splitting between the main slab and counter-slab in which the original specimen was preserved. However, in a 2002 lecture and corresponding abstract for the Society of Vertebrate Paleontology, paleontologist Nick Longrich suggested that these specimens actually preserve remnants of the original coloration pattern the animal would have exhibited in life. He argued that the dark, banded stains on the tail were too evenly spaced to have been caused by random separation of the fossil slabs, and that they represent fossilized pigments present in the feathers. Additionally, rather than an artifact of preservation or decomposition, the presence of dark feathers along only the top of the body may also reflect the color pattern in life, indicating that *Sinosauropteryx prima* was countershaded with dark coloration on its back and lighter coloration on its underside, with bands or stripes on the tail for camouflage.

#### Controversy

Some researchers have interpreted the filamentous impressions around *Sinosauropteryx* fossils as remains of collagen fibers, rather than primitive feathers. Since they are clearly external to the body, these researchers have proposed that the fibers formed a frill on the back of the animal and underside of its tail, similar to some modern aquatic lizards.

This would refute the proposal that *Sinosauropteryx* is the most basal known theropod genus with feathers, and also questions the current theory of feather origins itself. It calls into question the idea that the first feathers evolved not for flight but for insulation, and that they made their first appearance in relatively basal dinosaur lineages that later evolved into modern birds.

## Paleoecology

*Sinosauropteryx*, as a Yixian Formation dinosaur, is a member of the Jehol Biota, the assemblage of organisms found in the Yixian Formation and overlying Jiufotang Formation. The Yixian Formation is composed largely of volcanic rocks such as andesite and basalt. Between the volcanic layers are several beds of sedimentary rocks representing deposition in a lake. The freshwater lake strata of the Yixian Formation have preserved a wide variety of plants, invertebrates, and vertebrates. Gymnosperm forests were extensive, with a few early flowering plants as well. Ostracods and insects were diverse, and bivalves and gastropods were abundant. Mammals and birds are also well known from the formation. The setting was subject to periodic mortality events including volcanic eruptions, wildfires, and noxious gases erupting from the lakes. The climate has been interpreted as temperate, with distinct wet and dry seasons. The yearly temperature during this time period averaged about Template:Convert, indicating a temperate climate with unusually cold winters for the generally warm Mesozoic era, possibly due to northern China's high latitude during this time.

## JPInstitute.com Description

Sinosauropteryx has been called one of the most exciting scientific discoveries in decades. This Chinese fossil clearly shows defined feathers around much of this little dinosaur! It was a small, swift hunter that could not fly, but it seems to demonstrate that dinosaurs were beginning to look and act more like birds. It may be related to the little dinosaur, Compsognathus.

Sinosauropteryx continues to be a very important fossil for a number of reasons. First, and perhaps most importantly, it is a critical piece of evidence supporting the argument that birds descended from dinosaurs. Additionally, depending on its exact classification, it shows that at least some non-avian coelurosaurs were feathered.

The exact use of the feathers will be debated for some time. They are clearly not flight feathers, but they may have been used for insulation, courtship display, individual identification, or a combination of all of these.

## Dinosaur Field Guide Description

Sinosauropteryx ("Chinese lizard wing) was probably the most important dinosaur discovered in the 1990s. Before it was found, paleontologists had shown that birds were the descendants of theropods, meat-eating dinosaurs. However, they did not know when certain bird-like features first appeared. That's because many of the things that make birds special among all living animals are soft features that don't fossilize well. One of these soft features is feathers. Some paleontologists suspected that many of the theropod dinosaurs were actually covered by feathers or fuzz, but they could not find proof. Then, in 1996, an amazing discovery was made in northeastern China. In a series of rocks called the Yixian Formation, the skeleton of a small theropod was found. This little dinosaur was very similar to Compsognathus, a slightly older dinosaur from Germany. The bones of the skeleton were complete, but the most interesting thing about the fossil was the traces of small fibers surrounding the bones. These fibers turned out to be protofeathers, a simple type of body covering that developed into feathers in birds and their closest relatives. Since 1996, many feathered dinosaurs have been found in the Yixian Formation, but Sinosauropteryx is the most primitive of the feathered dinosaurs found to date. Because the Yixian dig has revealed that Sinosauropteryx, as well as its more advanced relatives, had feathers or protofeathers, paleontologists now realize that almost all the advanced meat-eating dinosaurs had this covering. This includes not only little dinosaurs like troodonts (see Sinornithoides) and alvarezsaurs (see Shuvuuia), but also medium-sized forms like ostrich dinosaurs (see Pelecanimimus and Gallimimus), oviraptorosaurs (see Oviraptor and Caudipteryx), and dromaeosaur raptors (see Sinornithosaurus, Velociraptor, and Deinonychus). Even Tyrannosaurus, Gorgosaurus, and the other tyrant dinosaurs which are more advanced than Sinosauropteryx) probably had protofeathers when they were hatchlings, but some scientists think that they might have shed these as they grew up. You might wonder why the Yixian Formation was able to preserve the soft features of these dinosaurs, while other rocks did not. The mud that became the Yixian Formation is very fine-grained- that is, the particles that make it up are very small. Because of this, small details were not blurred out. Also, because these dinosaurs were preserved in a quiet lake-like environment, rather than in muds dumped by a flooding river or sands blown around by sandstorms, the bodies of the dinosaurs were not damaged before they were covered over with mud. Thanks to this lucky circumstance, we now know much more about the outsides of these dinosaurs!

### Fun Facts

Although its name means "Chinese lizard wing," Sinosauropteryx did not have wings, nor could it fly. In fact, its warms were so short that they could barely scratch its knee!

### Trivia

The scientists who discovered Sinosauropteryx at first thought that dinosaurs could not have feathers, so they called it a bird.

## Appearance in other media

### *Jurassic Park*

* Sinosauropteryx appeared in Jurassic World: Alive as a common dinosaur.
* Sinosauropteryx appeared in Jurassic Park III: Park Builder.
* Sinosauropteryx appears in Jurassic World Evolution 2, via the Feathered Species Pack, released March 30th, 2023.

## Links

http://web.archive.org/web/20031008004155fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_sinos.html#

## References

1. ↑ Ji, S., Gao, C., Liu, J., Meng, Q., and Ji, Q. (2007). "New material of *Sinosauropteryx* (Theropoda: Compsognathidae) from western Liaoning, China." *Acta Geologica Sinica (English Edition)* **81**(2):177-182.
2. ↑ Gishlick & Gauthier (2007). "On the manual morphology of *Compsognathus longipes* and its bearing on the diagnosis of Compsognathidae." *Zoological Journal of the Linnean Society*, **149**: 569–581.
3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 Cite error: Invalid `<ref>` tag; no text was provided for refs named `chenetal1998`
4. ↑ Ji, Q., and Ji, S. (1997). "Advances in *Sinosauropteryx* Research." *Chinese Geology*, **7**: 30-32.
5. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `jiji1996`
6. ↑ Hurum, Jørn H.; Luo, Zhe-Xi & Kielan-Jaworowska, Zofia (2006): Were mammals originally venomous? *Acta Palaeontologica Polonica* **51**(1): 1–11.PDF fulltext
7. ↑ Currie, P.J. and Chen, P.-j. (2001). "Anatomy of *Sinosauropteryx prima* from Liaoning, northeastern China." *Canadian Journal of Earth Sciences*, **38**(1): 705-727.
8. ↑ Longrich, N. (2002). "*Sinosauropteryx* systematics." *62nd Annual Meeting of the Society of Vertebrate Paletontology*, 80A.
9. ↑ Lingham-Soliar, T *et al.* (2007) *Proc. R. Soc. Lond. B* doi:10.1098/rspb.2007.0352.
10. ↑ Access : Bald dino casts doubt on feather theory : Nature News
11. ↑ 11.0 11.1 Cite error: Invalid `<ref>` tag; no text was provided for refs named `zhou2006`
12. ↑ Wang, Y.; Zheng, S.; Yang, X.; Zhang, W.; and Ni, Q. (2006). "The biodiversity and palaeoclimate of conifer floras from the Early Cretaceous deposits in western Liaoning, northeast China." *International Symposium on Cretaceous Major Geological Events and Earth System*. p. 56A.
13. ↑ Template:Cite journal