Integrating allometry for accurate identification of Anura fossils from the Naracoorte Caves World Heritage Area

Abstract Understanding the morphology of fossil remains is essential for reconstructing past biodiversity and ecosystems. In palaeoherpetology, geometric morphometrics is widely used to identify fossils; yet, allometric variation—how shape changes with size—remains underexplored, especially in species with indeterminate growth, such as frogs. We applied a form-based geometric morphometric approach (shape and size) to the ilia of all 12 extant frog species in South Australia’s south-east to identify Late Pleistocene fossil specimens from the Naracoorte Caves World Heritage Area (NCWHA). Our results confirmed that species exhibit unique allometric trajectories and that snout–vent length can be estimated from the distance between the ventral and dorsal acetabular expansions. Ilial morphology aligned broadly with ecological groupings but was more effective at distinguishing species. Both shape-only and form-based analyses produced mostly consistent fossil identifications, though confidence levels varied. Twelve fossils were confidently assigned to extant taxa or ecotypes using both analyses, including Limnodynastes tasmaniensis, Limnodynastes dumerilii, Crinia signifera, and a new fossil record of Neobatrachus pictus for the NCWHA. These findings demonstrate the importance of accounting for allometric effects on morphology in fossil classification and enrich interpretations of the Quaternary fossil record.