| The soft-bodied macrofossils of the Vendian period (Neoproterozoic) have been the subject of much taxonomic and systematic speculation, often at a very high level. Much of this work has been done in a conceptual vacuum, since many questions about late Precambrian taphonomy, ecology, and functional morphology have never been posed, to say nothing of empirically investigated. There ought to be "reciprocal illumination" between the systematics of the Vendian fossils on the one hand, and their ecology, biogeography, function, and taphonomy on the other. Each aspect of their study can inform the others, can provide avenues to test hypotheses, and can suggest new hypotheses to be tested. My dissertation is based on my work with the fossils of the Vendian rocks of the Winter Coast of the White Sea, north of Arkhangel'sk, Russia.; Not all of these fossils are amenable to phylogenetic analysis, but I have carried out cladistic phylogenetic analyses of those groups of fossils that are complex enough to allow scoring of sufficient characters. These are the "frondlike" organisms and the arthropod relatives; I have also briefly reviewed the evidence for additional monophyletic taxa in the Vendian. My reconstructions are testable hypotheses based on explicit character definitions, which has not been typical of much of the work on the evolution of the Vendian organisms.; I have used the phylogenies as one component of a global biogeographic analysis of the Vendian biota, Brooks parsimony analysis or BPA, along with several non-phylogenetic methods of biogeographic analysis (phenetic and cladistic clustering algorithms). These yield consistent results and point to low provinciality, with the arrangement of localities by affinity corresponding well with one of the current paleotectonic models for the Vendian. Low provinciality and lack of a strong latitudinal diversity gradient also characterized the Vendian. Diversity-based ecological analyses of the White Sea biotas, coupled with comparative ecological studies on diversity of biotas around the world, suggest that communities of the Vendian were very different from living ones: there was little or no predation or epibiosis, many of the common taxa had extremely wide latitudinal and/or depth ranges, and in general, a very small number of factors controlled Vendian ecosystem structure. In turn, this allows certain systematic hypotheses to be falsified: organisms with a great depth range, for instance, cannot have been obligately photosynthetic organisms such as lichens or macroalgae. |
