Abstract
The Palaeognathae are a basal clade within Aves and include the large and flightless ratites and the smaller, volant tinamous. Although much research has been conducted on various aspects of palaeognath morphology, ecology, and evolutionary history, there are still areas which require investigation. This study aimed to fill gaps in our knowledge of the Southern cassowary, Casuarius casuarius , for which information on the skeletal systems of the syrinx, hyoid and larynx is lacking despite these structures having been recognised as performing key functional roles associated with vocalisation, respiration and feeding. Previous research into the syrinx and hyoid have also indicated these structures to be valuable for determining evolutionary relationships among neognath taxa, and thus be informative for palaeognath phylogenetic analyses, which still exhibits strong conflict between morphological and molecular trees. We documented variation across palaeognaths in the skeletal character states of the syrinx, hyoid, and larynx, using both the literature and novel observations (e.g. of cassowary). Notably the molecular moa-tinamou clade was found to share morphological character traits including the ossification of the cricoid and arytenoid cartilages, and an additional cranial character, the articulation between the maxillary process of the nasal and the maxilla. These findings contributed to optimisation of syrinx, hyoid and larynx characters showing increased phylogenetic support for palaeognath relationships derived from a molecular and morphological combined-data topology.