INTEGRATED AND FINELY-RESOLVED TIMELINES OF MID-PALEOZOIC BIOTIC AND ENVIRONMENTAL CHANGE IN THE PELAGIC REALM: OPPORTUNITIES AND OBSTACLES

Mid-Paleozoic times saw the demise of graptolites and chitinozoans, peak conodont taxon richness and the rise of ammonoid cephalopods. Because these rich clades have undergone taxonomic standardization for global biozonation, the sequence of their species-level first and last occurrences can resolve fine details of pelagic marine history. Daunting numbers of local taxon ranges, together with intervals of abrupt excursion in isotopic composition and facies, record the course of two mass extinctions and a long series of subordinate events in the coevolution of the global ocean and its pelagic occupants. Automated seriation programs can now render all this information into optimal composite global and local sequences. Including Cambro-Ordovician and Carboniferous buffer zones, which isolate undesirable end-effects, highly-resolved mid-Paleozoic timelines can now be built for graptolites (24,499 local range-end events of 2,291 taxa from 619 sections), conodonts (58,527; 4,334; 1,404), chitinozoans (8,752; 1,245; 228), and ammonoids (13,794; 2,893; 637). In the manner of graphic correlation, local taxon ranges are stretched, as little as possible, to identify global best-fit timelines. Subsequently, all local observed ranges are mapped back into the timeline of composite ranges as a means of quality control and as ensemble indicators of migration and extirpation. Local isotopic excursions, facies anomalies, and radioisotopic dates are treated as uncertainty intervals that shrink to fit. Uncertainty intervals and taxon ranges carry equal weight in the optimization. Emergent graptolite evolutionary rates appear to track global oceanic and climate change. Other clades differ in the timing of their responses. Although, the demands on data are less severe for these highly resolved time-lines than for detailed section-to-section correlation, there remain obstacles to progress. Foremost is a shortage of superpositional information from individual stratigraphic sections linking the various clades with one-another and with chemostratigraphic time series at the species level.