Pneumatisation and internal architecture of the Southern Cassowary Casuarius casuarius casque: a microCT study

Charlotte A. Brassey , Thomas O’Mahoney - School of Science and the Environment, Manchester Metropolitan University, UK; School of Earth and Environmental Science, University of Manchester, UK

Cranial ornaments such as keratinous horns and bony casques are commonplace amongst birds and take a variety of diverse forms. Possible functions include display, thermoregulation, vocalisation and intraspecific combat, yet few hypotheses have been directly tested. Here we investigate the anatomy and mechanics of the casque of the Southern Cassowary (Casuarius casuarius), and test functional hypotheses using CT-based virtual dissection.

In particular, we determine the nature of pneumatisation within the cassowary casque and explore the extent to which potential void spaces are connected to the airway and sinus system. We find the internal cavity of the casque to be poorly connected to the major sinuses, raising doubts over the degree to which sound could travel through the cranial structure. In light of these new insights into cassowary cranial anatomy, we consider a ‘resonance-chamber’ function for the casque unlikely, and suggest future research should focus on improving our understanding of cassowary behaviour and associated vocalisations.

How Amira-Avizo Software is used

The scans were reconstructed in XTek CTPro software (Nikon, Tring U.K) and exported to Avizo (FEI Visualisation Group, Oregon U.S.A.) for further processing. Highly mineralised components of the skull were automatically segmented in Avizo using a global greyscale threshold. Less mineralised components, including aspects of casque, sinuses and braincase were manually segmented using a combination of the threshold paint tool and top-hat tool. Resulting label fields were visualised using the surface render tool of Avizo.