The Genyornis egg: A commentary on Grellet-Tinner et al., 2016

When humans colonized Australia three giant flightless birds were on the landscape, of which the largest, Genyornis newtoni, the sole remaining taxon of the mihirungs, became extinct. Although nearly complete skeletons of Genyornis have been found, they never have been linked directly to an egg. Williams (1981) recognized and described distinct morphological characteristics demonstrating that eggshell fragments from two different taxa were preserved in arid-zone sand dunes. One type had characteristics identical to those of emu (Dromaius novaehollandiae), whereas the other was dissimilar to any extant bird. Based on its estimated volume exceeding that of modern emu egg, he attributed the newly discovered eggshell to Genyornis. Attribution of these eggshell to a Genyornis parent was recently challenged by Grellet-Tinner et al. (2016), who suggested that an extinct megapode of the genus Progura was a more likely candidate parent. They refer to the eggshell Williams (1981) assigned to Genyornis as putative Genyornis oological material (PGOM), which for convenience we follow here. The goal of this commentary is to support our claim that Genyornis is by far the most likely candidate parent bird for PGOM, and to show why it is highly unlikely that any megapode could be parent to PGOM.