HOLLIDAY, CM; WITMER, LM; Ohio University; Ohio University: Anatomical domains within sauropsid heads and their significance for functional interpretation of extinct taxa

Heads are busy places, involving the intersection of numerous vital systems comprised of, for example, muscular, respiratory, 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 feeding and auditory apparatuses. Other domains relating to the orbital, oropharyngeal, and antorbital cavities, etc., can also be identified. Attributes of these domains provide functional, behavioral, and phylogenetic insight into an animal�s biology. Although our ultimate goal may be the detailed reconstruction of the soft tissues within a domain, the first step is recognizing the domain and identifying its interactions with other domains. For example, the �braincase� is often considered as just the skeletal unit housing the brain. However, braincases themselves encompass the boundaries of several functional domains. In fact, it may be these boundaries (e.g., the orbitotemporal crest) that provide as much if not more insight into morphological evolution than the domains themselves, highlighting spatial competition and constraints among organ groups. We identify a number of bony interdomain boundaries that cross various braincase bones. In most cases, the soft tissues that correspond to these boundaries can also be identified (e.g., tensor periorbitae, middle ear sac), allowing the assessment of which components are contained within a domain (e.g., MAME profundus) 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.