Quantifying the gastral mass in Early Cretaceous ornithuromorphs (Aves: Ornithothoraces) from the Jehol avifauna

Some birds intentionally ingest stones to facilitate digestion of hard foodstuffs, a behavior inherited from non-avian dinosaurs and present in some of the earliest birds, as evidenced from clusters of gastroliths preserved within the abdominal cavity of a wide range of dinosaurs and Cretaceous birds. For the first time, high-resolution computed laminographic and computed tomographic scans were used to reconstruct the gastral mass in two species of non-neornithine ornithuromorph birds from the Lower Cretaceous Jehol Group. Four specimens of each taxon were analyzed. Preservation of the gastral mass in most of these specimens is in situ and regarded as complete or nearly so. The number of gastroliths, their total volume, and their total mass relative to the estimated body mass were calculated for each specimen. The resultant gastral mass-to-body mass ratios fall within the range observed in extant birds, supporting previous inferences that the digestive system in non-neornithine ornithur...