Meeting Abstract
The cranial casques (i.e., bony and keratinous dorsal skull projections) of extant cassowaries (Casuarius) have been of interest to researchers since the 17th century due to their conspicuousness. Casque biological roles, however, remain poorly understood, limiting our understanding of the life history of these unique birds as well as the selective conditions under which cranial elaborations appear in archosaurs. A strict focus on adult ornaments has left surprisingly few links to ontogeny, life history, and function. Moreover, the handful of osteological interpretations of casques are contradictory, illustrating the difficulty by which full documentation of this anatomy has proceeded. Four primary hypotheses for casque function have been proposed: (1) ramming, (2) vocalization, (3) thermoregulation, and (4) display. To address these roles, we undertook μCT analyses of cranial anatomy in a developmental series of southern cassowaries (C. casuarius), capturing details of external and internal structures as well as timings of sutural fusions and inflations of casque elements. We compared the developmental timing of casques to physical, behavioral, and reproductive maturity to determine the plausibility of each function. Our sample (n = 110) indicates the majority of casque growth occurs prior to sexual maturity; however, casque morphology continues to change substantially throughout adulthood. In C. casuarius casque deviation from midline is common, and such asymmetries appear to be primarily dextral. Form does not support functions for physical ramming or vocalization. Thermoregulation and display are not refuted by developmental anatomy and adult phenotype, necessitating more focused study.
