Lower Turonian Euramerican Inoceramidae: a morphologic, taxonomic, and biostratigraphic overview

摘要: The bivalve family Inoceramidae first evolved in the Permian and became extinct at the close of the Mesozoic. Inoceramids became dominant elements of many level-bottom communities, and they achieved global dispersion during the Jurassic and Cretaceous, especially during intervals of restricted benthic oxygen and black-shale deposition. Many groups appear to have been specifically adapted, in terms of anatomy and morphology (Kauffman and Harries, 1992), and possibly through chemosymbioses (Kauffman, 1988b; MacLeod and Hoppe, 1992), to chemically deleterious benthic environments. They are also found, however, in a wide range of different facies types/environments (from basinal black shales to nearshore sands), which suggests that they had relatively wide ecological tolerances at the genus and species level. The majority of inoceramid species had intercontinental or cosmopolitan distribution, mirroring the widespread nature of their preferred habitats, their broad adaptive ranges, and probably long-lived planktotrophic larvae; large larval shells are known from a few species. Despite their broad distribution, the Inoceramidae appear to have evolved very rapidly, with species ranges commonly averaging 0.2-0.5 Ma. This greatly enhances their use in biostratigraphy, and contrasts to the" normal" evolutionary rates of bivalves (2 Ma; see Stanley, 1979) and to the evolutionary hypothesis that cosmopolitan taxa should have slow evolutionary rates because of the wide dispersion of their component populations.Despite the fact that the Inoceramidae have been studied intensively for over a century, there are still a wide range of …