Sinocalliopteryx, meaning “Chinese beautiful feather,” is a genus of compsognathid dinosaur from the Early Cretaceous Period (124.6 million years ago) from China. It was recovered from the Jianshangou beds of the Yixian Formation. The type species, S. gigas, meaning “giant,” was derived from the dinosaur’s large size for a compsognathid. It is also unique from 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.
Like many theropods found in the Yixian Formation, Sinocalliopteryx was preserved with “proto-feathers,” small filamentous structures covering the skin, similar to that found in Sinosauropteryx. The structures differ in length across the body, with the longest proto-feathers covering the hips, base of the tail, the back and the thighs. The longest structures measured up to 4 inches in length. Proto-feathers were also found on the upper part of the foot, indicating that foot-feathers first appeared in dinosaurs much more primitive than previously known.
The well-preserved skeleton of Sinocalliopteryx contained the partial leg of a smaller dromaeosaurid within its abdominal cavity, consisting of a complete lower leg and foot with toes and claws in their natural, articulated position. While the leg is quite large in relation to the abdominal cavity, it is clearly situated within it, lying between the ribs. Ji and colleagues, describing Sinocalliopteryx in 2007, suggested that the finding could indicate that it preyed on the smaller, bird-like dinosaur. The discovery also indicated that it 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 leg, four irregularly-shaped stones were found in the abdomen, with no similar stones present in any other portions of the skeleton or found in the surrounding rock. The rocks were most likely gastroliths similar to those found with Nqwebasaurus and Baryonyx.
While Sinocalliopteryx was similar to the related Huaxiagnathus, it was larger, and at 7.75 feet in length, it is the largest known compsognathid genus. The large size compared to its relatives is also notable, and may indicate a trend towards large size among compsognathids, which are generally well-known for their smaller size compared to other, giant theropod dinosaurs.