Significance of abrasion patterns in Recent pectinoid bivalve shells

Abrasion, a taphonomic process of three-dimensional alteration and destruction of skeletal morphology after death of the animal and abidance in the Taphonomic Active Zone (TAZ), causes characteristic alteration and destruction patterns in Recent and fossil bivalve shells. We describe abrasion in shells of the Recent bivalves Aequipecten opercularis (Linnaeus) and Mimachlamys varia (Linnaeus) from high-energy macrotidal sandy beaches of Brittany (western France), the Algarve (Portugal) and Wales (UK). Following a revised, comprehensive description of the original shell morphology characteristic external and internal alteration is documented. We demonstrate that taxonomically relevant characters are reduced, altered considerably or even obliterated by abrasive processes which make a correct identification of the respective specimen difficult or impossible. Fracture specimens of abraded and non-abraded shells were analysed to test the role of shell microstructure within the abrasion process. Examples of abrasion in fossils are compared with the Recent material. Knowledge and consideration of abrasion patterns should avoid that new taxa, especially in the fossil record, are established on the basis of abrasion stages