REVISING AND UPDATING QUATERNARY CHRONOLOGIES IN THE NEOTOMA PALEOECOLOGY DATABASE FOR COMMUNITY PALEOECOLOGY

Community paleoecology is a potentially powerful tool for understanding the stability of ecological communities during long-term climate shifts like the Pleistocene-Holocene transition; however, it requires the capacity to accurately estimate species occurrences based on the fossil record. Public fossil biodiversity databases make large data sets available for these analyses, and the Neotoma Paleoecology Database in particular can handle a variety of geochronologic data. In this project, we are reassessing and updating the chronologies available in Neotoma for late Quaternary (<21ka) terrestrial mammal fossil sites in North America, in order to make a consistent and updated set of chronologies available for paleoecological studies, including our own planned trait-based study of small mammal community assembly. Neotoma already contains 9602 geochronological dates from 2068 collections at 1860 such sites, the majority (90%) radiocarbon and the remainder obtained by various other techniques. We have also added 1279 new dates from existing sites and 2781 dates from 1260 new sites by comparison with the Canadian Archeological Radiocarbon Database, and we plan to scrape additional dates from the xDD corpus. The precision and accuracy of each date is assessed using a rubric based on the nature of the material dated, the precision of the date, and the strength of its association with the vertebrate remains.

The dates are then compiled into chronologies for each analysis unit, and the new chronologies added to the database. Calibrating the radiocarbon dates in OxCal produces an age probability distribution for each sample. 72% of analysis units have only one date, and for these the chronology is identical to that of the single date in the absence of other information. For analysis units with multiple dates, we project a combined chronology based on OxCal’s estimated median lower and upper time boundaries for the whole set of dates. Age estimates for non-radiocarbon dates are made based on their own properties and added to the estimated chronology. Where possible, we will compute additional chronologies based only on high-quality dates. We will also analyze new samples in those cases where a single new high-quality date would contribute substantially to the time and space coverage of the data set.