Associations of corals and boring bivalves since the late cretaceous

The fossil record of coral and boring mytilid bivalves IS investigated. Middle Miocene associations from Austria, Hungary, and Turkey are described. As host corals,Montastrea, Porites, Siderastrea, Solenastrea, and Tarbellastraea can be noted. Eocene (Waschberg Zone) and Upper Cretaceous (Gosau Formation) examples are presented from Austria only. As host corals,Favia and Montastrea, respectively, Astrocoenia and an unidentified branching coral are recorded. The associated bivalve species are all mytilid Lithophaga, including L. laevigata (Quoy & Gaimard) in Tarbellastraea, a new Middle Miocene species in Montastrea, and L. alpina (Zittel) in Astrocoenia, the latter two from Styria, Austria. The characteristic features of the coral-bivalve relationships include (in massive corals): Boreholes more or less in the direction of coral growth, radially arranged, elongate boreholes, produced by keeping pace with coral growth. Bivalves were not only present near the surface, but deep inside the skeleton, representing successive generations in the same host colony. After the death of borers, their tunnels were closed by coral overgrowth. Cup-shaped false floors in the boreholes are correlated to reduced coral growth, indicating individual longevity of bivalves. The spacing of the floors mirrors the growth rate of the host coral (like its density bands), their number representing the minimal age of the respective bivalve. References to probable associations of coral and mytilid boring bivalves are given. It is quite likely that they have occurred since Jurassic times and probably since the Upper Triassic. So far, they have been ascertained since the Upper Cretaceous in massive and branching corals.