Revisiting the Cambrian Series 1 animal origination chronology

Oregon State University, Corvallis OR

Investigators

Abstract

The oldest shelly sea creatures appeared ~540 million years ago in the ‘Cambrian explosion’. This research seeks to refine the timeline for this captivating evolutionary event. This task is harder than expected because fossils of the same organism appear at different times in different places. How can one tell which of the many fossils of the same species is oldest—and refine its evolutionary timeline—with a sparse chronology for Cambrian marine sediment deposition and fossil occurrences? This research uses a computer program to match up the globally synchronous chemical signals of carbon cycle changes preserved in the rocks hosting Cambrian fossils. Matching the chemical signals from a fossil’s location to the one Cambrian location with many dates will allow these ages to be determined via extrapolation. As most Cambrian fossil organisms are the earliest members of still-living taxonomic phyla, our research promotes the progress of scientific inquiry into the tempo of evolution within and across animal clades. This project will develop open source, interactive software for the broader geological community to align chemical records without the need for advanced coding experience; train one PhD student and three undergraduates in computational research; and develop and distribute curricula, based on this new software, to promote undergraduate quantitative literacy. The chronology for the early Cambrian radiation of small skeletal fossils arises from visual alignment of δ13Ccarb excursions at a U-Pb radiometrically calibrated, fossil barren, stratigraphic section in Morocco to excursions at richly fossiliferous, time uncertain sections elsewhere. Visual δ13Ccarb correlation methods cannot ensure unique alignments, nor a given chronology. This research adopts a dynamic programming algorithm to identify libraries of geologically permissible alignments between fossiliferous stratigraphic sections and the Moroccan δ13Ccarb–U/Pb age model. Each permissible δ13Ccarb alignment will generate a distinct chronology for the local first appearance datum (FAD) of all fossil taxa at a stratigraphic section and, thus, various combinations of local FAD chronologies will yield alternative ages for a taxon’s global FAD. The proposed research explores whether/how alternative global FAD chronologies reveal a different number of origination pulses and alternative ages for pulse initiation and duration, thereby addressing heretofore unacknowledged uncertainty in the earliest Cambrian explosion chronology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.