Beneath the waves: Extraordinary dietary insights from a dismembered ichthyosaur from the lower Cretaceous

Abstract

Marine reptile lineages thrived throughout the Mesozoic era and are known to have performed diverse roles in marine ecosystems. Ichthyosaurs are characterized by their often dolphin-like convergences and thunniform bodies, having evolved a variety of forms and sizes that presumably represent niche diversity within their bauplan. Here, we report a spectacular discovery from the Lower Cretaceous of Australia: a dismembered adult ichthyosaur, Platypterygius australis (∼6–7 m in length), with preserved gut contents alongside massive bite marks on its skeleton that together, illuminate its role as both predator and prey within the Eromanga Basin marine ecosystem. Numerous bite marks are preserved on the vertebral centra of the ichthyosaur; some are split with corresponding halves missing, suggesting evidence of oral processing. Given their size, the bite marks were likely inflicted by the largest marine predator in the region, the pliosaur Kronosaurus queenslandicus. The gut contents of the P.australis specimen were preserved as globular concretions, likely formed from the ichthyosaur's spilt digestive tract. Neutron tomography NT scanning revealed one of these concretions contained fragments of fish, cephalopods, and two pterosaur bones, including a dentary fragment. The pterosaur dentary fragment was identified as a near-exact match to a previously unnamed taxon within Ornithocheiroidae. This discovery provides the first definitive evidence of food web interactions among these three groups and marks the first recorded instance of an ichthyosaur consuming a pterosaur or part thereof.