Are some fossils better than others for inferring palaeogeography?: The early Ordovician of the North Atlantic region as an example

Abstract

ABSTRACT Different kinds of fossils have different patterns of palaeogeographical distribution. This has led to differing palaeocontinental reconstructions in the early Palaeozoic. We take the early Ordovician of the North Atlantic region as a test case to investigate the influence of taxonomic group upon palaeogeographical interpretation. Using both single linkage duster analysis and parsimony methods of biogeographical analysis on fossil faunas and floras of various groups within this region it is shown that the patterns of similarity obtained, and their relationship to supposed oceanic separations, vary widely from one group to another. Some planktic fossils (graptolites, acritarchs) do not ‘see’ a separation between Gondwana and Baltica which is strongly supported by evidence from other groups. Trilobites and ostracodes, in particular, reveal patterns which conform well with other geological and geomagnetic evidence. At least in the Arenig‐Uanvirn time period, geographical separation is seen as a more important control on faunal composition than was biofacies. Considering the ‘better’ fossil groups for biogeographical discrimination, different analytical methods produce similar biogeographical results.