GEOLOGICALLY LONG-RANGING OSTRACODES: INFLUENCES OF VERTICAL AND HORIZONTAL RANGES

Intuitively, we expect geologically long-ranging marine fossil taxa to have greater vertical (bathymetric) and horizontal (geographic) ranges than short-ranging taxa because they have had more time to populate greater areas and/or because they may have lower extinction probabilities due to their broad distributions. Widespread taxa are however more likely to be sampled than spatially restricted taxa, hence differences in sampling probabilities may cause a correlation between duration and range. So, are long-ranging taxa really long-ranging because they are ecologically tolerant (occupying more depth zones and geographic areas) or are they apparently longer-ranging than shorter-ranging taxa simply because they are sampled more often? I have compiled geographic, bathymetric and geologic range information for a large family of marine Ostracodes (Trachyleberididae s.l.) from the literature and museum specimens. Ostracodes are extensively used in biostratigraphic studies and hence age and geographic data are abundant and available. Rather than focusing on survivorship across pre-identified extinction boundaries, I examine the relative geologic durations of species and genera in relationship to their geographic ranges and depth distributions. I explore the dataset both globally and regionally to partially account for differential sampling. Preliminary results show that the more depth categories a genus occupies, the longer its geologic duration. In contrast, species having greater depth ranges or occupying more depth categories do not have significantly longer geologic durations. Both latitudinal and longitudinal ranges are significantly positively correlated with geologic ranges for both species and genera, although the relationship is stronger for genera. It appears that part of this variation in the strength of the relationship between genera and species is due to the fact that longer ranging genera tend to consist of a greater absolute number of member species with potentially greater bathymetric and geographic ranges. In fact, preliminary results show that geographically widespread genera comprise widespread species members. I will present patterns of relationships between temporal, bathymetric and geographic ranges after rarifying and jackknifing the data to account for sampling.