Skull morphology of the enigmatic Genyornis newtoni Stirling and Zeitz, 1896 (Aves, Dromornithidae), with implications for functional morphology, ecology, and evolution in the context of Galloanserae

ABSTRACT

The presence of Dromornithidae in the Australian Cenozoic fossil record was first reported in 1872, yet although eight species and hundreds of specimens are known, key information on their morphology remains elusive. This is especially so for their skulls, which contributes to a lack of resolution regarding their relationships within Galloanserae. The skull of the Pleistocene dromornithid, Genyornis newtoni, was initially described in 1913. Additional fossils of this species have since been discovered and understanding of avian skull osteology, arthrology, and myological correlates has greatly advanced. Here we present a complete redescription of the skull of Genyornis newtoni, updating knowledge on its morphology, soft-tissue correlates, and palaeobiology. We explore the diversity within Dromornithidae and make comprehensive comparisons to fossil and extant galloanserans. Furthermore, we expand on the homologies of skull muscles, especially regarding the jaw adductors and address the conflicting and unstable placement of dromornithids within Galloanserae. Findings support generic distinction of Genyornis newtoni, and do not support the close association of Dromornithidae and Gastornithidae. We thus recommend removal of the dromornithids from the Gastornithiformes. Considering character polarities, the results of our phylogenetic analyses, and palaeogeography, our findings instead support the alternative hypotheses, of dromornithids within, or close to, the Suborder Anhimae with Anseriformes.

KEYWORDS:

• Skull morphology
• Homology
• Galloanserae
• Musculus adductor mandibulae externus
• Functional morphology

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/08912963.2024.2308212.

Acknowledgments

There are many people who contributed to this research, who we would like to acknowledge. Firstly, Adam Yates provided access to many MAGNT specimens, including NTM P932-2 (Figure 8), and patiently allowed us to keep the specimens for longer than initially stated. Adam Yates and Sam Arman both assisted with answering questions on the specimens available from MAGNT. Mary-Anne Binnie (SAMA), Maya Penck (SAMA), Katie Date (NMV), Lisa Nink (FU), and Kristen Spring (QM) also loaned us material and/or gave us access to their collections. We thank Lawrence M. Witmer (Ohio University) for his generosity in providing a micro-CT scanned skull of Presbyornis pervetus (USNM 299846). We would additionally like to acknowledge Patricia Vickers-Rich and Peter Murray for their extensive monograph on the Dromornithidae (Murray and Vickers-Rich, 2004); Warren Handley (FU) contributed to data analysis on gastroliths; Jacob van Zoelen (FU) who provided guidance in using Blender v. 2.93.2 (Blender Online Community, 2023); Michael S. Y. Lee for tutelage with regards to phylogenetic methodologies and photographs of dromornithid fossil from MAGNT; Peter Trusler for interesting and useful discussions; Mahala Fergusen for photographing specimen SAMA P10838; and Joseph Bevitt who kindly took time to scan the specimen SAMA P59516 using the neutron scanner at ANSTO which was a big contribution to understanding the internal structure of the fossils and the scanning potential for the Lake Callabonna Genyornis newtoni material. We also thank three anonymous reviewers who contributed to improving the manuscript. We would like to thank the other Chief Investigators for the Australian Research Council grant DP180101913 (Extricating extinction histories at Lake Callabonna’s megafauna necropolis) which funded the collection of material from Lake Callabonna, namely Lee Arnold and Anusuya Chinsamy-Turan. Additionally, all the people who conducted fieldwork at Lake Callabonna and contributed to preparing the fossils, primarily Carey Burke who spent many months cleaning and preparing the specimens use in this study, Aaron Camens, and Keith Cook (Maxim Foundation) who made large contributions to the field work at Lake Callabonna. Finally, thank you to Gerard and Karina Sheehan for the access to Lake Callabonna that allowed this work to transpire.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

PLM made the morphological observations, conducted the comparisons, and created the initial drafts of the manuscript. THW provided physical access to, and/or photographs of, many specimens, as well as the field work and funding required to conduct this research (Australian Research Council grant DP180101913, see below). THW and PLM conceived the project as part of the larger project this work has contributed to, namely investigating the biology of Genyornis newtoni, and forms a part of PLM’s PhD thesis. PLM, JCB and THW contributed to research and interpretations regarding relevant morphology and palaeobiology. JCB provided detailed and significant contributions to the understanding of myological and syndesmological correlates of osseous structures, and their homologues across the specimens, taxa and publications studied (Appendix Three). The assembly of morphological character descriptions and states, and subsequent coding of all taxa was undertaken by PLM, which was revised and edited by PLM and JCB. JCB ran the phylogenetic analyses, and JCB and PLM interpreted results and wrote associated sections. PLM created all figures aside from Figures 4 and 12 (and part of 14) which were produced by JCB. All authors participated in associated field work. All authors contributed to editing the manuscript and approved the submitted version.

Data availability statement

All data generated or analysed during this study are included in this published article, the appendices and supplementary information files.

Additional information

Funding

Funding was provided from the Australian Research Council grant DP180101913 (Extricating extinction histories at Lake Callabonna’s megafauna necropolis) and THW was sponsored by the Maxim Foundation Ltd in 2021.