Possible Cephalopod Reproductive Mass Mortality Reflected by Middle Carboniferous Assemblages, Arkansas, Southern United States

Abstract

Middle Carboniferous cephalopod assemblages across northern Arkansas are dominated by a small number of ammonoid species that occur in unusual abundances. Individuals of a particular species exhibit strikingly similar size, yet both small and large species are represented. Assemblages occur in either high energy deposits of conglomeratic sandstone or oolite, or low energy concretionary, dark shales, but in neither case do they seem to have undergone post-mortem sorting. Ammonitellas and protoconchs are notably absent in the matrix preserving the ammonoids in both settings. These assemblages may represent sexually mature adults that experienced mass mortality following reproduction (semelparity) in a manner similar to that found in some modern squids.