Mauritian snail shells show evidence of extinct predators

Shells of several species of Tropidophora land snails of the volcanic island of Mauritius (Mascarenes, SW Indian Ocean), all dated between ~1426BCE and ~1090 CE predating the earliest confirmed human discovery (1519) and settlement (1638) of the island, have been found with characteristic predatory holes. These are either large, irregular holes on the underside of T. carinata, or circular holes 0–9–3.3 mm in diameter, in almost the exact same place in T. ligata, T. icterica and T. michaudi. The former have been suggested to be evidence of predation by the extinct red rail Aphanapteryx bonasia, which we consider to be probable. The circular holes have not been reported previously. Examination of these shows them to be very regular in shape and size, to be in the centre of a shallow depression marked by two sets of fine grooves at right angles to one another. These holes were compared to damage caused by predators reported to have ‘bored’ into shells: Drillus elaterid beetles, Poiretia spiraxid snails and rathouisiid slugs. The damage is most similar to that caused by rathouisiids and we postulate that the holes were caused by a now extinct predator of that family. The only extant members of the family in the Mascarene islands are too small to be the predators. There is no evidence of such predation in recent shells; this is an extinct interaction between an extirpated predator and its prey.