Failed predation in Late Ordovician gastropods (Mollusca) from Manitoulin Island, Ontario, CanadaThis article is one of a selection of papers published in this Special Issue on the themeThe dynamic reef and shelly communities of the Paleozoic. This Special is in honour of our colleague and friend Paul Copper.

Abstract

Shell repairs resulting from presumed failed predation are documented in gastropods from the Late Ordovician (Cincinnatian; Richmondian) mid-to-upper Kagawong Submember of the Georgian Bay Formation on Manitoulin Island, Ontario, Canada. The bryozoan–mollusc biota and associated sediments generally suggest nearshore, shallow (<10 m), low energy (lagoonal), and perhaps mesotrophic to eutrophic conditions. Two sample sets from this unit have been studied for shell repair. One of the more commonly applied estimates of shell repair frequencies involves division of the number of individuals with at least one scar by the total number of individuals in the sample (the Individuals with scars method). Using this calculation, 207 specimens of Lophospira trilineata Ulrich and Scofield yielded a shell repair frequency of 4.8%; in 28 specimens of Trochonemella sp. the shell repair frequency was 35.7%. Repairs in Trochonemella occur primarily in the larger size class, suggesting that a size refuge was achieved by this species. Low repair frequencies in L. trilineata suggest predation with a higher success rate or fewer encounters. This study demonstrates that the paradigm of a standardized low level of shell repair in Ordovician and Silurian gastropods is oversimplistic and a range of frequency rates can be expected.