Biogeographic analyses of the Ediacara biota: a conflict with paleotectonic reconstructions

Paleotectonic reconstructions for the late Proterozoic have differed over t he timing of the Cordilleran rifting between Laurentia and the East Gondwan a cratons. Parsimony Analysis of Endemism (PAE) and phenetic clustering of the "Ediacara biota" were carried out, for comparison with competing paleot ectonic hypotheses. All analyses show a common pattern of similarities amon g biotas. The biotas of Charnwood Forest and Newfoundland consistently grou p together, while the south Australian biota is closest to those of Baltica , northern Laurentia, and Siberia. The biota of southwest North America, th ough still poorly known, strikingly resembles that of Namibia-not that of n orthwestern Canada. This pattern is not obviously due to facies-related or preservational bias and is very different from Cambrian biogeographic patte rns. The overall pattern is most consistent with the hypothesis that the we stern margin of Laurentia was in close contact with East Gondwana, with rif ting taking place either during or just before the Vendian. This arrangemen t has been previously proposed as a paleotectonic hypothesis; however, most recent paleomagnetic and structural studies support the alternate hypothes is that this rifting took place more than 100 million years before the Vend ian. Resolving this contradiction will require much more data on both organ ismal distribution and cratonal position.