GLOBAL CHANGES IN RUDIST BIVALVE DIVERSITY AND EFFECTS ON EARLY CRETACEOUS GULF COAST COMMUNITIES

Rudist Bivalves (Hippuritida Newell) first evolved during the late Jurassic about 160 Ma, diversified throughout the Cretaceous and became extinct about 66 Ma (Steuber et al., 2016, Treatise Online 00:1–00). Diversification events during the late Barremian–early Aptian, late Albian–middle Cenomanian, and Campanian were punctuated by at least five extinction events in mid-Valanginian, early to mid-Aptian, latest Albian, latest Cenomanian, and late Maastrichtian when the group became extinct. Three of these five events coincided with major oceanic anoxic events that particularly affected rudists with aragonitic shells. Calcite-dominated genera diversified during the Late Cretaceous. Numerical ages of first and last occurrences of genera were calibrated by Strontium isotopes or graphic correlation with a global database. Rudist endemism increased during late Campanian–Maastrichtian resulting in centers of high diversity in the Caribbean and Arabia. This increasing endemism may have been an important early milestone on the road to final extinction.

In the Caribbean Province rudists were principal contributors to carbonate fixation and sediment production during the Barremian-Albian. Geometries and species composition of rudist biostromes and bioherms on the interior shelf differed from those at the shelf margin. Successions of caprinoids, radiolitids and requieniids formed low relief mounds on the shelf interior; at the shelf margin corals, cyanobacteria, caprinids, and requieniids formed complex ecosystems.

Rudists of the Family Caprinuloideidae Damestoy were the main members of buildup paleocommunities and diversified from Barremian through Albian followed by near extinction in the latest Albian with few Cenomanian genera surviving on Mexican atolls. Barremian-early Aptian assemblages were composed of Huetamia, Pantojaloria, Caprina, Douvillelia, and Amphitriscoelus. Early Albian assemblages were dominated by Caprinuloidea , Coalcomana and Planocaprina. Middle Albian assemblages were composed of Caprinuloidea, Youngicaprina and Texicaprina species. Genera of late Albian assemblages were Kimbleia, Neokimbleia, Mexicaprina, and Youngicaprina, and Immanitas and Jalpania populated Mexican atolls.