Paleobiogeographic patterns in the morphologic diversification of the Neogene planktonic foraminifera

Statistical analysis of a literature-based compilation of latitudinal ranges, phylogenetic relationships and biometric measurements of 135 Neogene planktonic foraminiferal species yielded several well-defined relationships between paleobiogeographic distribution and morphology. When cosmopolitan species originate, they tend to be relatively small and morphologically conservative. As keeled forms develop and the Neogene radiation invades other areas of shape space, the cosmopolitan species also shift in the same direction, but continue to lag behind and remain at the conservative end of the shape and size distribution. A significant positive correlation exists between species longevity and geographic range, and significantly greater longevities in species that range into the subpolar and polar habitats when compared with those that donʹt. A similar relationship was found in speciation rates: lineages that range into the polar and subpolar habitats have lower speciation rates than those that do not. This relationship holds true when keeled forms are removed from the analysis. Furthermore, when species ranging into the polar/subpolar habitats are removed from the data, the difference in speciation rate between keeled and unkeeled forms is not significant. It appears that a speciesʹ extension into or beyond the subpolar realm has a stronger statistical relationship with its probability of speciation and its longevity than its total latitudinal range. Comparison of latitudinal ranges for ancestor–descendant pairs reveals a significant trend toward reduction of range for new species.