The Evolution of the Antorbital Cavity of Archosaurs: A Study in Soft-Tissue Reconstruction in the Fossil Record with an Analysis of the Function of Pneumaticity

ABSTRACT The most commonly cited apomorphy of Archosauriformes is an opening in the snout known as the antorbital cavity. Despite the ubiquity and prominence of the antorbital cavity, its function and importance in craniofacial evolution have been problematic. Discovering the significance of the antorbital cavity is a two step process: first, establishing the function of the bony cavity (that is, its soft-tissue relations), and second, determining the biological role of the enclosed structure. The first step is the most fundamental, and hence is examined at length. Three hypotheses for the function of the antorbital cavity have been advanced, suggesting that it housed (1) a gland, (2) a muscle, or (3) a paranasal air sinus. Thus, resolution is correctly viewed as a “soft-tissue problem,” and is addressed within the context of the extant phylogenetic bracket (EPB) approach for reconstructing the unpreserved features of fossil organisms. The soft-anatomical relations of the antorbital cavity (or any bony st...