First record of lithophagy in Sulcusuchus erraini (Plesiosauria; Polycotylidae) with comments on the taphonomic and collect bias in gastroliths

Gastroliths have long been reported in marine reptiles and are particularly well documented inelasmosaurid plesiosaurs, while their occurrence in short-necked polycotylids is notably rare. Here,we report the first documented occurrence of lithophagy in the polycotylid plesiosaur Sulcusuchuserraini Gasparini mean = 0.7, standarddeviation = 0.1) and the Oblate – Prolate index (OP; mean = 0.08, standard deviation = 4.71) suggestsa probable fluvial origin. To assess the potential taphonomic bias on Ψ and OP values, two analyseswere performed: one using correlation and a second one considering resampling analysis. The resultsof both indicated that the mean index values remain robust even with up to 50% loss of the gastrolithcluster. The maximum transverse section observed (12.24 cm2) within the gastrolith cluster suggeststhat S. erraini possessed a relatively large oesophagus compared to other plesiosaurs analyzed.