Structure and function of the cassowary's casque and its implications for cassowary history, biology and evolution

Abstract

Cassowaries (Casuarius) possess a cranial casque, sheathed by keratin and composed of modified cranial bones. We combine data and hypotheses on three areas of cassowary research. First, we present novel observations on casque anatomy. The bony core is fragile, incorporating a mass of trabeculae anteriorly and an empty space posteriorly. Secondly, we use these observations to evaluate hypotheses of casque function. Implications that the casque evolved within the context of activities involving percussive actions are unlikely and observations that might support these hypotheses are absent. It is most likely that the casque serves a sociosexual role and functions in visual and acoustic display. The similarity in casque form between males and females, combined with male parental investment, makes it plausible that the extravagant structures present in cassowaries evolved within the context of mutual sexual selection. Thirdly, we combine morphological, molecular and geological evidence to provide a new phylogenetic history for cassowaries. We suggest that cassowaries invaded New Guinea in at least two waves and provisionally regard crown-cassowaries as a geologically young, post-Pliocene clade. We provide these hypotheses as areas requiring discussion and urge other workers to test our ideas with new data on cassowary anatomy, behaviour and genetics.

High diversity of the Ganzhou Oviraptorid Fauna increased by a new “cassowary-like” crested species

“…These spaces (pneumatic diverticula) are irregular in shape and differ in size, reminiscent of conditions seen in the modern cassowary. The inner, bony core, casque of the cassowary 25 is made by irregularly-arranged, slender bony struts called trabeculae 25 . Corythoraptor jacobsi possessed an extensive cranial casque that was probably composed of the skull roofing bones: nasals, frontals and parietals (Fig.…”

“…These delicate trabeculae outline empty cavities, the largest exposed of which is 6.6 × 14.3 mm large, which implies that the inner core was light, fragile (perhaps pliable), and hence, not suitable for percussive behavior including intraspecific combat. The largest opening (called concavity by Naish and Perron 25 ) is in the posterior part of the crest located above the external narial opening (see Supporting Information Fig. S1).…”

“…Rugose external surface suggests that cranial casque was likely covered by outer keratinous sheath in Corythoraptor as well. The shell-like outer layer of the casque is approximately 2-3 mm thick in the cassowary 25 and 2 mm thick in Corythoraptor .…”

“…and 3) sociosexual hypothesis partly overlap with the acousting hypothesis as more efficient low-frequency communication linked to more strongly resonating casque evolved under sexual selection. Recent cassowaries produce low-frequency casque-directed vocalizations towards a partner during mating season 25, 39 . Low-frequency sounds, however, are made inside the throat apparatus in the cassowaries 25 and there is no morphological evidence for such behavior in oviraptorids.…”

A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials

“…To help hear these vocalisations, koalas have large auditory bullae (Louys et al, 2009). Cassowaries have a highly pneumatised casque that may be used as an acoustic organ for social and sexual display (Naish and Perron, 2014). The large sinuses found in extinct marsupial megafauna such as Diprotodon, may have functioned to produce, amplify and receive low frequency vocalisations.…”