Anatomy ofSinosauropteryx primafrom Liaoning, northeastern China

Abstract

A spectacular pair of Sinosauropteryx skeletons from Jurassic–Cretaceous strata of Liaoning in northeastern China attracted worldwide notoriety in 1996 as the first dinosaurs covered with feather-like structures. Sinosauropteryx prima is important not only because of its integument, but also because it is a basal coelurosaur and represents an important stage in theropod evolution that is poorly understood. Coelurosauria, which includes (but is not limited to) dromaeosaurids, ornithomimosaurs, oviraptorosaurs, troodontids, and tyrannosaurids, formed the most important radiation of Cretaceous carnivorous dinosaurs in the Northern Hemisphere. It also includes Aves. Sinosauropteryx prima has a number of characters that were poorly preserved in known specimens of the closely related Compsognathus longipes from Europe. These include the longest tail known for any theropod and a three-fingered hand dominated by the first digit, which is longer and thicker than either of the bones of the forearm. Both specimens have a thick coat of feather-like structures, which seem to be simple branching structures. The claim that one skeleton of Sinosauropteryx has preserved the shape of the liver is unsupportable, if only because the fossil had collapsed into a single plane, which would have distorted any soft, internal organs.