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Paleocene pareorine turritellid gastropods from the Pacific slope of North America
This paper presents the first detailed study of Mesalia martinezensis (Gabb, 1869) and Mesalia clarki (Dickerson, 1914a), the only two known pareorine (spout-bearing) turritellid gastropods from the Pacific slope of North America. Both species are redescribed, in light of new morphologic information that also confirms their assignment to genus Mesalia Gray, 1847, which we believe to be congeneric with Sigmesalia Finlay and Marwick, 1937. New stratigraphic information allows for refinement of the chronologic range of each species. Mesalia martinezensis is of early late Paleocene (late Danian) to early late Paleocene (early Thanetian) age and ranges from northern California to northern Baja California. Mesalia clarki is of late middle to early late Paleocene age (late Selandian to early Thanetian) age and is known only from California; in southern California it is restricted to a coralline-algal facies. Both species have considerable variability in their spiral sculpture. Mesalia originated during either the Late Cretaceous (Maastrichtian) in northern Africa or the early Paleocene (Danian) in northern Africa and western Iran. It became widespread during the warm (greenhouse) conditions of the Paleocene and Eocene but became geographically restricted during subsequent cooler global conditions. Mesalia is an extant genus with possibly six species, and whose total geographic range is in coastal waters in southern Portugal, southern Spain, Mediterranean Sea (primarily the western part), Canary Islands, and the west coast of northern Africa.