INITIAL SURVIVAL OF MESOZOIC MARINE GENERA: A ROLE FOR GEOGRAPHIC RANGE BEYOND TEMPORAL AND TAXONOMIC HETEROGENEITY

Initial survival of marine animal genera beyond their first stage of occurrence is more common among those with broad geographic ranges, but in previous analyses of the Mesozoic this simple association was not detected. We examine survivorship trends in Mesozoic data from the Paleobiology Database to determine whether the trend is really absent or merely masked by other variables.

We used logistic regression to predict genus survival as a function of narrow versus broad geographic range. Broad range does not correlate with survival when Mesozoic data are aggregated. When stage-to-stage differences in overall survivorship rates are included in the survivorship model, however, broad geographic range does have a small significant correlation with survival. Similarly, when membership within taxonomic classes is included in the model, geographic range has a small significant correlation with survival. A model including both temporal and taxonomic heterogeneity shows that widespread range has a large effect on survival, though still not as strong as during the Paleozoic or Cenozoic.

Influence of major extinction events might be expected to alter overall survivorship sensitivity within the Mesozoic. In contrast to the typical association between range and survival, we find that cephalopod genera are much more likely to survive during mass extinction intervals if they have an initially restricted range. More specifically, cephalopod survival is independent of range during mass extinction stages (Rhaetian, Pliensbachian, Maastrichtian) but is highly correlated with restricted range in aftermath stages (Induan, Hettangian, Toarcian). When mass extinction intervals are disregarded, Mesozoic cephalopod survival is correlated with broad geographic range. The few reversals of selectivity in cephalopod survival are enough to obscure the importance of range when all cephalopods are aggregated through the Mesozoic, and when cephalopods are aggregated with other animal genera. When cephalopods are excluded, widespread range significantly predicts survival.