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Sinocalliopteryx (meaning 'Chinese beautiful feather') is a genus of compsognathid dinosaur from the Lower Cretaceous Yixian Formation of China (Jianshangou Beds, dating to 124.6 Ma). While similar to the related Huaxiagnathus, Sinocalliopteryx is larger, and at 2.37 meters (7.78 ft) in length, it is the largest known compsognathid genus, and the large size of this "giant compsognathid" lent Sinocalliopteryx its specific name, S. gigas, meaning 'giant.'[1] Sinocalliopteryx is also distinguished from Huaxiagnathus, as well as other compsognathids, by its relatively long hands in relation to its arms, which were also longer overall than in most compsognathids, a feature possibly related to its size.

DescriptionEdit

Sinocalliopteryx was a bipedal predator. The preserved length of the holotype specimen is 237 centimetres. Its weight was estimated by Gregory S. Paul in 2010 at twenty kilogrammes.[1] Sinocalliopteryx is distinguished from Huaxiagnathus, as well as other compsognathids, by its relatively long hands in relation to its arms. The arms and hindlimbs were also longer overall than in other compsognathids, a feature possibly related to its size.

Sinocalliopteryx had an elongated head with a pointed snout, showing a convex upper profile. There were four teeth in the premaxilla which were small but exceptionally had denticles on their front edges. Only six, larger, teeth were present in the maxilla of the holotype specimen but the number of its tooth positions could not be adequately determined. Specimen CAGS-IG-T1 preserves ten maxillary tooth sockets with room for one or two more in damaged areas. The jugal was a strongly built element with a high-rising front branch that formed part of the lower front edge of the eye socket. The lower jaw lacked an opening in its outer side.[2][3]

The vertebral column consisted of eleven cervical, twelve dorsal, five sacral and at least forty-nine caudal vertebrae. The point of the tail is missing. In the tail, the spines and chevrons strongly inclined to the back. The gastralia had very short lateral segments.[2]

The arm had a short humerus and also the lower arm was short and elegant with an ulna showing only a weakly developed olecranon process on its back upper end. The hand was very elongated though, as long as the ulna and upper arm combined. The second metacarpal was expanded at the top at the side of the first metacarpal, making the entire metacarpus more compact. The second claw was elongated, as long as the thumb claw. The third metacarpal was rather short and carried a thin, third, finger.[2]

In the pelvis there was a little notch in the front edge of the ilium. The relatively long shaft of the ischium curved downwards. The hindlimb was elongated, largely because of a long lower leg, having 90% of the length of the thighbone. The foot was also long, especially in the metatarsus.[2]

Like many other theropods of the Yixian Formation, Sinocalliopteryx was preserved with "protofeathers," simple filamentous integument (hairlike structures covering the skin), very similar to that found in Sinosauropteryx. The integument of Sinocalliopteryx differ in length across the body, with the longest protofeathers covering the hips, base of the tail, and back of the thighs. These longest protofeathers measured up to ten centimeters (4 in) in length. Interestingly, protofeathers were also found on the metatarsus (upper part of the foot). While these were not nearly as long or modern as the corresponding feathers of "four-winged" dinosaurs such as Microraptor and Pedopenna, they do indicate that foot-feathers or similar structures first arose in dinosaurs much more basal or "primitive" than previously known.

Discovery and speciesEdit

The type species Sinocalliopteryx gigas was named and described in 2007 by Ji Shu'an, Ji Qiang, Lü Junchang and Yuan Chongxi. The generic name is derived from Sinae, Latin for the Chinese and Greek καλός, kalos, "beautiful", and πτέρυξ, pteryx, "feather". The large size of this "giant compsognathid" lent Sinocalliopteryx its specific name, gigas, meaning 'giant'.[2]

The holotype, JMP-V-05-8-01, was discovered at Hengdaozi, in Sihetun, in Liaoning Province, from the Jianshangou Beds of the Yixian Formation dating from the Barremian-Aptian, about 125 million years old. It consists of a nearly complete skeleton with skull, compressed on a single plate, of an adult individual. Extensive remains of protofeathers have been preserved.[2] In 2012 a second specimen was described, CAGS-IG-T1, of an individual larger than the holotype. The skull was about 10% longer, the feet about a third, a difference explained by positive allometry. The specimen consists of a partial skull, tail, hands, feet and ribcage. It shows filaments on the tail.

PhylogenyEdit

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