Patterns and processes of evolutionary stasis and change in Eratoidea (Gastropoda: Marginellidae) from the Dominican Republic Neogene

After more than 20 years of intensive investigation of the tempo and mode of evolutionary change in the fossil record, a striking discordance in evolutionary patterns within and among clades has emerged. Whether such discordance is real and a fundamental pattern in the history of life or an artifact of comparisons among species from different clades, temporal scales, geographic regions, and paleoenvironmental regimes, remains unknown. This study investigated the patterns of morphological evolution in three species within Eratoidea, a marginellid gastropod clade, through an extensively sampled and studied stratigraphic sequence (Middle Miocene to Early Pliocene) from the Dominican Republic Neogene. This investigative system permits comparison of evolutionary patterns within a morphologically appropriate group (enabling the separation of ontogenetic and evolutionary change) from the same paleoenvironmental context and temporal interval. Morphological evolution was examined in relation to lithology, paleoenvironment, geography, and time. Concordant evolutionary patterns occurred in Dominican Eratoidea species. Morphological evolution was best characterized as oscillatory stasis: no net morphological change occurred through a five-million year sequence and little statistically significant morphological variation was correlated with geography, paleoenvironment, lithology, or time. Nevertheless, some intraspecific morphological oscillations occurred that were correlated with bathymetric and faunal change. A broad environmental tolerance in unstable shallow marine paleoenvironments, coupled with similar intrinsic thresholds, appear to be controlling concordant evolutionary patterns in Eratoidea. More studies comparing evolutionary patterns in similar systems over comparable timescales are necessary to explore the causes of discordance of evolutionary pattern within and among clades in the fossil record.