Sinosauropteryx

Sinosauropteryx (meaning 'Chinese reptilian wing', simplified Chinese: 中华龙鸟; traditional Chinese: 中華龍鳥; pinyin: Zhōnghuá lóng niǎo; literally: 'Chinese dragon bird') is a compsognathid dinosaur. Described in 1996, it was the first dinosaur taxon outside of Avialae (birds and their immediate relatives) to be found with evidence of feathers. It was covered with a coat of very simple filament-like feathers. Structures that indicate colouration have also been preserved in some of its feathers, which makes Sinosauropteryx the first non-avialian dinosaurs where colouration has been determined. The colouration includes a reddish and light banded tail. Some contention has arisen with an alternative interpretation of the filamentous impression as remains of collagen fibres, but this has not been widely accepted. Sinosauropteryx was a small theropod with an unusually long tail and short arms. The longest known specimen reaches up to 1.07 metres (3.51 feet) in length, with an estimated weight of 0.55 kilograms (1.21 pounds) It was a close relative of the similar but older genus Compsognathus, both genera belonging to the family Compsognathidae. Only one species of Sinosauropteryx has been named: S. prima, meaning 'first' in reference to its status as the first feathered non-avialian dinosaur species discovered. Three specimens have been described. The third specimen previously assigned to this genus represents either a second, as-yet unnamed species or a distinct, related genus. Sinosauropteryx lived in what is now northeastern China during the early Cretaceous period. It was among the first dinosaurs discovered from the Yixian Formation in Liaoning Province, and was a member of the Jehol Biota. Well-preserved fossils of this species illustrate many aspects of its biology, such as its diet and reproduction. 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. All described specimens of Sinosauropteryx preserve integumentary structures (filaments arising from the skin) which most palaeontologists interpret as very primitive type of feathers. These short, down-like filaments are preserved along the back half of the skull, the arms, neck, back, and top and bottom of the tail. Additional patches of feathers have been identified on the sides of the body, and palaeontologists 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 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.