Northeast Pacific Upper Cretaceous and Paleocene Glycymeridid Bivalves

Abstract

The Late Cretaceous to late Paleocene record of glycymeridid bivalves in the region extending from the Alaska Peninsula, southward to Baja California, Mexico is studied in detail for the first time.Glycymeris pacifica(Anderson, 1902), of late Cenomanian to late Turonian age, is the earliest known glycymeridid in the study area. Very locally, it is found with the middle to late TuronianGlycymeris yoloensisn. sp. The latter apparently represents some intermediate state between genusGlycymerisda Costa, 1778 and genusGlycymeritaFinlay and Marwick, 1937. In the study area,Glycymeritais represented byGlycymerita veatchii(Gabb, 1864), middle to late Turonian to late Campanian;Glycymerita banosensis(Anderson, 1958) new combination, late Campanian to latest Maastrichtian;Glycymerita aleutan. sp., known only from Alaska and of early Maastrichtian age; andGlycymerita major(Stanton, 1896) new combination, Selandian to Thanetian. All the studied species lived in warm-temperate, shallow-marine waters and were shallow burrowers in fine-grained siliciclastic sediments. Variability in morphology is common in sizeable populations of the various species, especiallyGlycymerita veatchii, which increased nearly fivefold in size during its 19.5 million-year-long range and culminated in shells up to 84 mm in length.