Endocranial Anatomy of the Giant Extinct Australian Mihirung Birds (Aves, Dromornithidae)

Abstract

Dromornithids are an extinct group of large flightless birds from the Cenozoic of Australia. Their record extends from the Eocene to the late Pleistocene. Four genera and eight species are currently recognised, with diversity highest in the Miocene. Dromornithids were once considered ratites, but since the discovery of cranial elements, phylogenetic analyses have placed them near the base of the anseriforms or, most recently, resolved them as stem galliforms. In this study, we use morphometric methods to comprehensively describe dromornithid endocranial morphology for the first time, comparing Ilbandornis woodburnei and three species of Dromornis to one another and to four species of extant basal galloanseres. We reveal that major endocranial reconfiguration was associated with cranial foreshortening in a temporal series along the Dromornis lineage. Five key differences are evident between the brain morphology of Ilbandornis and Dromornis, relating to the medial wulst, the ventral eminence of the caudoventral telencephalon, and morphology of the metencephalon (cerebellum + pons). Additionally, dromornithid brains display distinctive dorsal (rostral position of the wulst), and ventral morphology (form of the maxillomandibular [V2+V3], glossopharyngeal [IX], and vagus [X] cranial nerves), supporting hypotheses that dromornithids are more closely related to basal galliforms than anseriforms. Functional interpretations suggest that dromornithids were specialised herbivores that likely possessed well-developed stereoscopic depth perception, were diurnal and targeted a soft browse trophic niche.

The endocast of the insular and extinct Sylviornis neocaledoniae (Aves, Galliformes), reveals insights into its sensory specializations and its twilight ecology

“…In dorsal view, the telencephalon of S. neocaledoniae exhibits a morphology similar to that of many extant galliforms 22 , 36 , 40 : in dorsal and ventral view, the shape of the two cerebral hemispheres gives the rostral part of the endocast a pear-shaped or heart-shaped contour wider caudally. This morphology is much less marked than that of Acryllium vulturinum , Gallus gallus , O. guttatus , P. pileata and Guttera plumifera .…”

“…We are aware that these relative measurements could be biased by allometric factors related to the great size of the animal 25 : in order to minimize this bias, we also compare the endocranium of S. neocaledoniae with those of all other large birds (i.e., of body mass greater than 8.750 kg, for the statistical delineation) in addition to extant galliforms. All these comparisons are based on our own 3D-scans realized on various skulls of diverse species (see list in Supplementary Data) and on data extracted from the literature 22 , 33 – 36 .…”

Neuroanatomy of the mekosuchine crocodylian Trilophosuchus rackhami Willis, 1993

“…Technically, the term endocast refers to a cast (be it digital or physical) of any internal, hollow cavity (Balanoff & Bever, 2020 ). In many palaeoneurological studies, the cavity that accommodated the brain (encephalon) is often called the cranial endocast and/or simply endocast (e.g., Bever et al, 2011 ; Handley & Worthy, 2021 ; von Baczko et al, 2018 ; Witmer & Ridgely, 2009 ), with some authors using the term brain endocast as well (e.g., Brown et al, 2020 ; Herrera et al, 2018 ; Leardi et al, 2020 ). Here, the term brain endocast is used in reference to the endocast of the cranial cavity that housed the brain.…”

A new look at an old Australian raptor places “Taphaetus” lacertosus de Vis 1905 in the Old World vultures (Accipitridae: Aegypiinae)

“…There is no evidence that any other lineages of large, volant scavenging birds, such as the Teratornithidae of the Americas, were ever present in Australia. The large, flightless Dromornithidae of Australia, despite some claims to the contrary, were herbivorous (Murray & Vickers-Rich 2004;Handley & Worthy 2021), unlike the flightless, predatory Phorusrhacidae from the Americas.…”