Data from: 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
ornithuromorphs was comparable to that in extant taxa. Compared to
available data for non-volant non-avian theropods, the gastral mass is
proportionately smaller in birds suggesting that the evolution of flight
constrained gastral mass size in the theropod lineage. Currently,
available data on gastral mass characteristics suggests that Iteravis ate
larger food particles compared to Archaeorhynchus but cannot be utilized
to determine diet more precisely. Better understanding of the relationship
between gastral mass characteristics and food items across a broader range
of extant taxa may provide an indirect but important method through which
to infer diet and digestive function in archosaurs.