LATITUDINAL PREFERENCES IN CENOZOIC MOLLUSKS: A CHANGE FROM CONSERVATISM TO DYNAMISM WITH THE PASSAGE OF TIME
A Gaussian logistic regression model was used to parameterize the preferred latitude, latitudinal range, and peak abundance for marine bivalve and gastropod genera in the Paleobiology Database (www.paleodb.org) at global and oceanic scales. The correlation of these traits among all Cenozoic epochs was then used to assess the strength of conservatism.
Results demonstrate that preferred latitude is conserved between adjacent epochs, even when using a synoptic global dataset. More widely separated epochs, however, show progressively weaker correlations and do not support long-term conservatism. Instead, an increasing number of genera exhibit substantial changes in preferred latitude as more geologic time is added. This may be attributable to slow evolutionary changes in the latitudinal preferences of genera, differential extra-tropical and tropical extinction patterns, systematic shifts in sampling due to tectonic movements, or some combination thereof.
When the global data are partitioned into separate Atlantic and Indo-Pacific subsets, the Indo-Pacific appears to exhibit stronger and longer lasting conservatism in preferred latitude than either the Atlantic or the world as a whole. This difference may support previous observations that Indo-Pacific faunas are more conservative than their Atlantic counterparts, though Indo-Pacific correlations also degrade over time.
The remaining two parameters, latitudinal range and peak abundance, also show some degree of conservatism, but less so than preferred latitude. Error on estimates of both these parameters is higher than for preferred latitude, which suggests that the observed correlations between epochs may be stronger than indicated by these analyses. Future work will focus on improving estimates of these parameters by using a more flexible model that can account for kurtosis and skew in the latitudinal response curves of genera.