T252 Topics in Paleoecology: Modern Analogues and Ancient Systems III

Tuesday, 3 November 2015
1:30 PM - 5:30 PM
Room 315

FIVE MILLION YEARS OF RODENT PALEODIETS IN THE MEADE BASIN, GREAT PLAINS, USA

Paper number: T252-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

Faunas in the Meade Basin (MB) record evolutionary changes in the local small mammal community over the last 5 Myr, spanning the local evolution of modern C4–dominated grasslands and long-term climatic changes. We use carbon and oxygen isotope compositions of these faunas to reconstruct resource use by small mammals. Specifically, we characterize how food resources were partitioned within communities, and how diets varied through time in response to changing community membership, and environmental change.

Using LA-IRMS, we measured δ13C and δ18O values of tooth enamel from 70 taxa representing 6 small mammal lineages (N= 326). We compared the fossil data to isotopic values of modern MB specimens, which includes δ13C and δ15N values in hair (N = 196, 11 spp.) and collagen (N = 28, 4 spp.), and δ13C and δ18O values in bone carbonate (N = 30, 4 spp.).

Fossil δ18O values have no major temporal trends, but late Pleistocene fauna have lower values than Pliocene and modern faunas, which may reflect cooler Pleistocene climates. Small mammal δ13C values indicate they utilized C3 and C4 resources over the last 5 Myr as local C4 biomass increased from 40% to >70%. C4-dominated diets are not recorded in faunas until 3 MA, which may indicate lower C4 consumption or absence of C4-consuming taxa 5-3 MA. The δ13C values of both 3-2 MA and modern faunas span the full C3 plant to C4grass range.

The highest δ13C values prior to 3 MA are from an archaic vole, but Pleistocene and modern voles almost exclusively eat C3 derived resources. This suggests a dietary change between older voles with rooted molars and younger voles with ever-growing molars. Cricetids have the largest range in δ13C values (12‰), and their mixed C3:C4 diets likely reflect herbivory and invertivory (Onychomys and Peromyscus). Most Pliocene sciurid δ13C values vary between -28 and -19‰ and become more negative in the late Pleistocene. Modern Cynomys differ from all other sciurids with some δ13C values indicating C4-dominated diets. Heteromyids, (Dipodomys and Prodipodomys), have the most positive δ13C values throughout the record and differ from other heteromyids with C3-dominated diets. Our study documents differences in small mammal diets over the past 5 Myr, and provides insight into variations in resource partitioning among taxa during intervals of faunal and environmental changes.