Holliday, C. and Witmer, L.: ANATOMICAL DOMAINS WITHIN THE HEADS OF ARCHOSAURS AND THEIR RELEVANCE FOR FUNCTIONAL INTERPRETATION

HOLLIDAY, Casey, WITMER, Lawrence, Ohio Univ. Dept of Biological Sciences, Athens, OH

Heads are busy places, involving the intersection of numerous vital systems comprised of, for example, muscular, respiratory, nervous, and sensory components, all of which share a limited amount of cephalic space. Individually, each of these components represents a ‘functional domain’ with specific roles and spatial limits. For example, the adductor chamber and tympanic cavity are the domains related to, respectively, the masticatory and auditory apparatuses. Other domains relating to the orbital, oropharyngeal, nasal, and antorbital cavities, etc., can be identified. Attributes of these domains provide functional, behavioral, and phylogenetic insight into an animal’s biology. Although the ultimate goal may be the detailed reconstruction of the soft tissues within a domain, the first step is recognizing the domain and identifying its boundaries. A next step is determining how these domains interact and share space within the head. For example, paleontologists tend to think of the ‘braincase’ as a unit, perhaps with its major role being housing the brain. However, braincases themselves encompass the boundaries of several functional domains, such as, again, the eye, jaw muscles, and middle ear, but also the neck and pharynx. In fact, it may be these boundaries that provide as much if not more insight into morphological evolution than the regions themselves, highlighting spatial competition and constraints among organ groups. We identify a number of bony interdomain boundaries (e.g., otosphenoidal, ototemporal, orbitotemporal crests) that cross various braincase bones. In most cases, the soft tissues that correspond to these boundaries can be identified (e.g., tensor periorbitae, middle ear sac), allowing the assessment of which components are contained within a domain (e.g., MAME superficialis) and which span multiple domains (e.g., nerves, vessels). Given that the broad functions of each domain are well understood, differences among taxa in the relative size and conformation of the domains can provide critical functional insight. For example, maniraptorans expanded the cerebral and ocular domains at the expense of the adductor domain.