Sinocalliopteryx

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.' 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.

Paleobiology
Like many other theropods of the Yixian Formation, Sinocalliopteryx was preserved with "protofeathers," simple filamentous integument (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 10 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 primitive than previously known.

The well-preserved skeleton of Sinocalliopteryx contained the partial leg of a dromaeosaurid within the abdominal cavity, comprised of a complete lower leg and foot with toes and claws in their natural, articulated position. While the leg is very large in relation to the abdominal cavity, it is clearly situated within it, lying between the ribs. Ji and colleagues, who described Sinocalliopteryx in 2007, suggested that this could indicate it preyed upon the smaller, bird-like dinosaur. This discovery indicated that Sinocalliopteryx may have been an agile, active, "fierce" predator, especially since other compsognathids have been found with (presumably fast-moving) lizards and small mammals in their abdominal cavities.

In addition to the dromaeosaurid leg, four irregularly-shaped stones were found in the abdomen, with no similar stones present in any other portions of the skeleton or embedded in the surrounding rock. The authors interpreted these as gastroliths (gizzard stones) similar to those found with Nqwebasaurus and Baryonyx. Other theropods, such as Caudipteryx and a Mongolian ornithomimid, were also found with gastoliths, though in those cases the stones were much more numerous and smaller in size. Ji and colleagues speculated that, since the later two dinosaurs were probably primarily herbivores, the number and size of gastroliths may correspond with diet; that is, herbivores ingested many small stones, while carnivores ingested only a few larger stones to aid in digestion.

The large size of Sinocalliopteryx compared to its relatives is also notable, and may indicate a trend towards large size among compsognathids (a group well-known for their small size compared to other, giant theropod dinosaurs), similar to the trends towards larger sizes in other dinosaurian lineages.