Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs.

This article focuses on the osteological composition, development, and evolutionary significance of bony cranial ornaments (casques) in modern birds, specifically comparing palaeognathous (Casuarius casuarius) and neognathous species (Numida meleagris and Macrocephalon maleo). Using micro-computed tomography (µ-CT) imaging, the study identifies two broad patterns of casque construction: geminal, consisting solely of paired cranial bones typical of neognaths, and disunited, featuring both paired and unpaired midline bones as seen in the palaeognath Casuarius. The timing of casque development relative to sexual maturity varies among species, suggesting different functional roles in display and social signaling. The authors propose a framework for using modern avian cranial ornaments as analogues to interpret the structure, development, and potential functions of extinct archosaur cranial ornaments, emphasizing developmental timing, structural composition, and homology as key comparative criteria.