#35 - Enamel isotopes reveal late Pleistocene ecosystem dynamics in southeastern North America

The end of the late Pleistocene (~10,000 years ago) witnessed the extinction of over seventy percent of North America’s megafaunal genera. Although this pattern has been extensively investigated, its causal mechanisms remain elusive. Much of this difficulty is related to the spatial and temporal discontinuity of sites dating to the period leading up to the extinctions. Due to its removal from glacial conditions, southeastern North America provides a unique window into ecosystem dynamics just prior to human arrival in the region. In this study, we present new stable carbon and oxygen isotope data from Mammuthus columbiand Bison latifronsteeth collected from a well-dated Last Glacial Maximum (~20,000 rcybp) locality called Clark Quarry in coastal Georgia, USA. We compare these data to those from similarly aged (middle and late Rancholabrean) localities from Florida and demonstrate the presence of a vegetation gradient with elevated levels of C3vegetation at higher latitudes. We hypothesize that this pattern may have contributed to previously described migratory patterns of mastodon (Mammut) populations in southeastern North America. Serially-sampled δ13C and δ18O values suggest that Clark Quarry Mammuthus and Bison changed their diet seasonally with the incorporation of elevated quantities of C4vegetation during warmer periods. Our data indicate more exaggerated seasonal dietary variability in these taxa at Clark Quarry relative to those collected from the interglacial locality of Waccasassa River in Florida, providing additional evidence for the significant influence of glacial dynamics in structuring North American ecosystems

LATE PLEISTOCENE ECOSYSTEM EVOLUTION IN SOUTHEASTERN NORTH AMERICA: A TRANSDISCIPLINARY APPROACH USING FOSSIL AMERICAN ALLIGATOR ENAMEL ISOTOPES**

Existing research points to utilizing ancient ecosystem functionality as a means of understanding contemporary biological responses to climate change and human population expansion. In this study, we use enamel isotope values (δ13C, δ18O) from modern and fossil American alligators (Alligator mississippiensis) from the Clark Quarry Site Complex (CQSC; Brunswick, GA) dating to ~60,000 years ago to better understand the aquatic ecosystems and climatic conditions of coastal landscapes in southeastern North America during the late Pleistocene. In particular, we use these data as a proxy for the position of the CQSC relative to the paleoshoreline during this period, which has been variably hypothesized in the existing literature. Serially sampled δ13C values from modern alligator enamel (N=13; Jekyll Island, GA and Aiken, SC), after correcting for contemporary atmospheric CO2 levels, averaged -10.8‰ (±6.2), while δ18O values averaged 1.0‰ (±1.7). δ13C values from serially sampled fossil alligator enamel (N=14; CQSC) averaged 8.3‰ (±1.4), while δ18O values averaged -2.9‰ (±2.2). These data indicate that CQSC alligator δ13C values are intermediate between modern alligator samples characteristic of strictly marine (Jekyll Island, GA) or strictly freshwater (Aiken, SC) environments, and CQSC alligator δ18O values are depleted relative to those from all modern aquatic systems sampled here (freshwater, brackish and marine). These data suggest that 1) the CQSC was part of a brackish system during the late Pleistocene, and 2) southeastern North America was dominated by cooler ambient temperatures during this period. This pattern in temperature is also supported by δ18O values from CQSC megaherbivores (Mammuthus columbi, Bison latifrons). These enamel data indicate that the CQSC ecosystem was markedly different from those characteristic of the region today. Our findings can be used as an ecological framework for testing hypotheses related to the extinction of species due to climatic changes and the expansion of human populations during the late Pleistocene

Enamel isotopes reveal late Pleistocene ecosystem dynamics in southeastern North America

The end of the late Pleistocene (∼10,000 years ago) witnessed the extinction of over seventy percent of North America\u27s megafaunal genera. Although this pattern has been extensively investigated, its causal mechanisms remain elusive. Much of this difficulty is related to the spatial and temporal discontinuity of sites dating to the period leading up to the extinctions. In this study, we present new stable carbon and oxygen isotope data from Mammuthus columbi and Bison latifrons teeth collected from a well-dated Last Glacial Maximum (∼20,000 rcybp) locality called Clark Quarry in coastal Georgia, USA. This site lies in direct proximity to where Sir Charles Lyell collected the type specimen of M. columbi in 1846 and therefore is of added historical significance. We compare these data to those from similarly aged (Sangamonian interglacial and Wisconsin glacial intervals) localities from Florida and demonstrate the presence of a vegetation gradient with elevated levels of C3 vegetation at higher latitudes. Serially-sampled δ13C and δ18O values suggest that Clark Quarry Mammuthus and Bison changed their diet seasonally with the incorporation of elevated quantities of C4 vegetation during warmer periods. Our data indicate more exaggerated seasonal dietary variability in these taxa at Clark Quarry relative to those collected from the Sangamonian interglacial locality of Waccasassa River in Florida, providing additional evidence for the significant influence of glacial dynamics in structuring North American ecosystems. These high-resolution ecological patterns should be incorporated into hypotheses focused on extinction dynamics in southeastern North America and more broadly