Purported crushing teeth of actinopterygian fishes from the Late Cretaceous of Patagonia reinterpreted as crustacean bio-gastroliths

Since the 1980s, certain hemispherical structures discovered in Upper Cretaceous (Campanian-Maastrichtian) deposits of Patagonia have been interpreted as crushing teeth, variously attributed to indeterminate Teleostei or the semionotiform genus Lepidotes. This study examines the morphological, microscopic, and mineralogical characteristics of these structures, collected from the Allen, Los Alamitos, La Colonia, Loncoche, and Chorrillo formations, and compares them with modern and fossil fish crushing teeth. The external morphology, internal structure, and mineralogical composition (primarily phosphates and carbonates) of these structures, as analyzed in this study, correspond to crustacean bio-gastroliths rather than actinopterygian teeth. Microscopically, all examined gastroliths display a uniform banding pattern, while actinopterygian crushing teeth exhibit a two-layer organization with abundant dentinal tubules. These findings enhance our understanding of the distribution of crustaceans that produce gastroliths and also provide new insights into how taphonomic processes influence the mineralogical and microscopic structures of fossil gastroliths.