Meeting Abstract
The visual abilities of dinosaurs as they relate to ecology and behavior have been the subject of recent interest. Orbital soft tissues have received little attention, and, if ignored, the eyeballs of dinosaurs may be missized or positioned inaccurately, leading to poor estimates of visual fields and spurious conclusions about behavior and ecology. Fossils of extinct dinosaurs were studied firsthand to identify the osteological correlates (OCs) for orbital soft tissues including the extraocular muscles, cranial nerves, glands, eyelids, supraorbital membrane, subocular ligament, and nasolacrimal duct. Intact heads of 27 species of birds, crocodylians, and squamates were subjected to iodine-enhanced microCT (diceCT and spiceCT), and several dozen additional avian specimens were microCT-scanned without iodine contrast. Orbits were dissected to validate the CT studies and to identify the OCs for orbital soft tissues. Soft tissues and endosseous labyrinths were segmented in Avizo, and soft tissues were modeled in Maya. Estimates of eyeball size and optical parameters including focal length and monocular visual field, which depend in part on eyeball size, shape, and position, were modeled. Visual fields based on these optical parameters and constraints were modeled and tested against empirical measurement of visual fields in the literature. The results indicate that reconstructing accessory soft tissues in the orbits of extant diapsids can provide upper limits on estimates of eyeball diameter, axial length, and the geometry of visual fields, whereas lower limits are currently less constrained (although under study). Based on the findings from the CT and fossil studies, eyes, accessory soft tissues, and visual field geometry were modeled for several extinct archosaurs, including moa and early ornithischian dinosaurs.
