Sinosauropteryx was a small bipedal theropod, noted for its short arms, large first finger (thumbs), and long tail.

[3] A pigmented area in the abdomen of the holotype has been suggested as possible traces of organs,[2] and was interpreted as the liver by John Ruben and colleagues, which they described as part of a crocodilian-like "hepatic piston" respiratory system.

[6] 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.

[2] All described specimens of Sinosauropteryx preserve integumentary structures (filaments arising from the skin) which most palaeontologists interpret as a primitive type of feathers.

[2] 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 are closest 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 subcutaneous structures.

Microscopic examination shows that individual filaments appear dark along the edges and light internally, suggesting that they were hollow, like modern feathers.

[2] Though the feathers are too dense to isolate a single structure for examination, several studies have suggested the presence of two distinct filament types (thick and thin) interspersed with each other.

[3] 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.

In addition, the thick filaments preserve no evidence of Calcium phosphate, the mineral which modern feather quills are made of.

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.

[2] However, Longrich suggested in his 2002 presentation for the Society of Vertebrate Paleontology that these specimens actually preserve remnants of the colouration pattern the animal would have exhibited in life.

By examining melanosome structure and distribution, Zhang and colleagues were able to confirm the presence of light and dark bands of colour in the tail feathers of Sinosauropteryx like that of a Red panda.

From the presence of phaeomelanosomes, spherical melanosomes that make and store red pigment, they concluded that the darker feathers of Sinosauropteryx were chestnut or reddish brown in colour.

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.

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.

However, Currie brought a photograph to the 1996 meeting of the Society of Vertebrate Paleontology at the American Museum of Natural History in New York, causing crowds of palaeontologists to gather and discuss the new discovery.

The news reportedly left palaeontologist John Ostrom, who in the 1970s had pioneered the theory that birds evolved from dinosaurs, "in a state of shock.

[3][19] Feduccia's frill argument was followed up in several other publications, in which researchers interpreted the filamentous impressions around Sinosauropteryx fossils as remains of collagen fibres rather than primitive feathers.

Since the structures are clearly external to the body, these researchers have proposed that the fibres formed a frill on the back of the animal and underside of its tail, similar to some modern aquatic lizards.

However, this claim was also unsupported, with Smithwick et al. finding no evidence of the beaded structures which collagen hypothesis proponents identified on the specimens.

The study proposes that some areas of the fossil preserved in three dimensions cast shadows which would have resembled beaded structures in low quality photographs.

However, Smithwick et al.'s study noted that, after further preparation, this irregular surface was simply a layer of sediment with a different color than the rest of the slab.

Purported features of collagen fibers were in fact misidentified shadows formed by scratches or irregular sediment, a misidentification perpetuated by the low quality of early Sinosauropteryx photographs.

[1] These proposals have not been accepted, and Sinosauropteryx is generally classified in the family Compsognathidae,[2][3][14] a group of small-bodied long-tailed coelurosaurian theropods known from the Late Jurassic and Early Cretaceous of Asia, Europe, and South America.

Siamraptor Siamotyrannus Streptospondylus Xuanhanosaurus Poekilopleuron Piveteausaurus Piatnitzkysaurus Marshosaurus Leshansaurus Eustreptospondylus Condorraptor Asfaltovenator Sciurumimus Nedcolbertia Magnosaurus Duriavenator Afrovenator Compsognathus longipes Compsognathus corallestris Torvosaurus tanneri Torvosaurus gurneyi Megalosaurus Scipionyx Wiehenvenator Iberospinus Baryonychinae Spinosaurinae Allosauroidea (Incl.

[28] However, in a 2002 presentation and abstract for the Society of Vertebrate Paleontology, Nick Longrich showed that this specimen differs in several anatomical aspects from the others, including its relatively large size, proportionally longer shins, and shorter tail.

They found that it was a small primitive bird with a relatively high skull, blunt rostrum and a slightly high premaxilla; that the antorbital fenestra was elliptical but not enlarged, the dentary was robust, the surangular was narrow and elongated, and the dentition is extremely well developed and acute; that there are over 50 extremely elongated caudals, constituting 60% of the body length, and the forelimb is extremely short with a short and thick humerus; the pubis was elongated and extremely inflated at its distal end and the ischium is broad; the hind limb was long and robust, the tibia is only slightly longer than the femur, the tarsals are separated, and the metatarsals are relatively robust with unfused proximal ends; the feathers are short, small, and uniform; many ornament the top of the skull, cervical, and dorsal regions, in addition to the dorsal and ventral caudal region.

[1] The specimen NIGP 127587 was preserved with the remains of a lizard in its gut region, indicating that small, fast-moving animals made up part of the diet of Sinosauropteryx prima.

Hurum, Luo, and Kielan-Jaworowska (2006) 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.