Temporal and geographic size trends in Neogene Corbulidae (Bivalvia) of tropical America: using environmental sensitivity to decipher causes of morphologic trends
Abstract Because of their abundance and ubiquity, corbulid bivalves were significant components of the marine ecosystems affected by the environmental, oceanographic, climatic, and biotic changes that occurred during the Neogene in tropical America. Tropical American corbulids show dramatic changes in size over time and space. Eastern Pacific corbulids increase in size in the Holocene, whereas in the Caribbean and western Atlantic, size decreases from maxima in the middle and upper Miocene. As a result, size differences between living eastern Pacific and Caribbean/western Atlantic corbulids are statistically significant. Previously proposed causes of faunal trends in marine invertebrates of tropical America include changes in predation intensity, changes in productivity, and climatic cooling, all of which have been linked to the emergence of the Central American Isthmus (CAI). By comparing geographic and temporal patterns at both regional and local scales, it is possible to decipher the cause of corbulid size trends. Large corbulid species tend to occur in deposits that show evidence of increased nutrient availability, either from upwelling or coastal runoff, and tend to be excluded from units deposited under more oligotrophic conditions. Regional size trends in corbulid bivalves, therefore, are best explained by a general decrease in nutrient availability and productivity in the Caribbean/western Atlantic as the CAI emerged.