INTEGRATION OF PALEOBIOGEOGRAPHY AND PALEOGEOGRAPHY: EVIDENCE FROM ARENIGIAN NAUTILOID BIOGEOGRAPHY

A better understanding of paleobiogeography can be realized by attributing the distri- bution of taxa to various factors of the physical environment. Since such factors were dependent upon the arrangement of landmasses, coeval paleobiogeography and paleogeography should be comple- mentary, providing both are reasonably accurate. A method of analysis is presented which aids in the description and interpretation of paleobiogeography in this context. A probabilistic index of similarity is used to compute the similarity of faunas based on the number of shared taxa where the frequency of taxa in the whole data set is used to adjust for the differing probability of occurrence of taxa (cosmopolitan versus endemic). Non-metric multidimensional scaling and principal components anal- ysis are used to reduce the dimensionality of the similarity matrix and ordinate the final configuration. Relating the position of faunas on the principal axes of this configuration to environmental factors responsible for the taxonomic composition of the faunas provides a means of integrating the paleo- biogeography and paleogeography. Analysis of distributional data for 186 Arenigian nautiloid genera indicates that nautiloid paleo- biogeography for this period was largely dependent on three biogeographic barriers: distance across deep-ocean floor and along expanses of continuous shelf, emergent portions of landmasses, and dif- ferences of the neritic and oceanic environments.