Gastropod egg capsules preserved on an Early Cretaceous ammonite from Daghestan, Russia

• Gastropod egg capsules are reported from the Lower Cretaceous for the first time.
• They were likely produced by neritimorphs within empty ammonite shell.
• Preserved attachment bases of the capsules suggest they hatched.
• Ammonite shells served as sheltered spawning ground for gastropods.
• Sediment-filled shell created specific conditions for egg capsules preservation.

Tiny, circular objects preserved in the form of rims have been detected on an Early Cretaceous (early Aptian) ammonite from Daghestan, Russia. They are preserved on the body chamber portion of the mould, where they occur either as isolated rims or, more commonly, as structures closely neighbouring with each other. Comparisons with similar Recent and fossil structures indicate that they are remnants of gastropod egg capsules preserved as attachment bases, and most probably were produced by neritimorph gastropods. The egg capsules were deposited within an empty ammonite body chamber where the gastropods found a site sheltered against potential scavengers and predators. The occurrence of only attachment bases indicates, that the egg capsules may have hatched. Although they are preserved in the form of iron oxides, during fossilization the originally organic egg capsules underwent pyritization followed by later weathering. This is the first record of this kind from the Lower Cretaceous.