Abstract

The Upper Cretaceous teleost assemblage represented by otoliths from the Severn Formation (Maastrichtian) of Maryland (USA) is identified, and evaluated in the context of Upper Cretaceous otolith assemblages from the USA. Otoliths were analyzed from five localities, and the species diversity (richness and evenness) was assessed for all sites combined and individually. Examination of 2296 otoliths resulted in 32 taxa identified to at least the genus level. This represents one of the most diversified otolith assemblages known for the Cretaceous. The Severn Formation has a unique occurrence of Siluriformes (54.10% of total) and Beryciformes (25.95%), and possible factors for this preponderance are investigated. The Severn Formation also produced a small number of otoliths of the Gadiformes, which represents the earliest in the Atlantic Coastal Plain. Percentage similarity measurements calculated for each of the sites varied from 65.68% to 4.30%. The variance of the similarity values are believed to be related to changes in the shallow marine environment including estuaries, deltas, freshwater input, and nutrient shifts. The beryciforms are thought to have been highly adapted to specialized environments, much like the perciforms of the Cenozoic, and the variances at different sites (from no specimens to 31.28%) may have been related to localized changes in the paleoenvironment. The percentage of beryciforms and siluriforms was also examined at eight other localities in the USA and pointed to an inverse relationship in their abundance. The Severn Formation otolith assemblage is a member of the Appalachian Community bioprovince. One new taxon is described as a putative polymixiiform: Severnichthys bourdoni gen. et sp. nov.