Stable isotope records of inland California megafauna -- New insights into Pleistocene paleoecology and paleoenvironmental conditions.

摘要

Paleodietary studies of California megafauna have focused primarily on the coastal late Pleistocene Rancho La Brea tar seeps (RLB) in Los Angeles, while other sites remain understudied. This study examined two Pleistocene fossil localities from inland California (San Joaquin Valley) and report δ 13C and δ18O values measured from tooth enamel of mammalian megafauna at both sites. The late Pleistocene McKittrick tar seeps in Kern County have a similar fauna to RLB. The middle Irvingtonian (~700,000 year old) Fairmead Landfill site, near Chowchilla, contains a megafaunal assemblage dominated by Equus, Camelops and Mammuthus. .;This study uses stable isotope values measured in carnivore and herbivore tooth enamel to investigate paleodietary and paleoecological patterns at both sites. The δ13C values of tooth enamel are controlled by diet and can be used to investigate resource usage and partitioning among and between taxa. In large mammals δ18O ratios are controlled by drinking water, and by proxy, climate. Ontogenetic serial tooth δ 18O and δ13C reveal seasonal trends in resource usage, from which we can infer patterns of forage availability.;Stable carbon values from 16 taxa, reveal significant differences both between taxa and between localities. Faunal δ13C differ significantly (p<0.001) between Fairmead and McKittrick, ranging from -13.5 / to -8.2 / and -11.8 to -0.7‰, respectively. No significant differences were detected in δ18O between sites ( p=0.7).;Fairmead Landfill δ13C values are consistent with an environment dominated by C3 vegetation. Platygonus and Camelops had the lowest and highest δ13 C, respectively. Camelops exhibited the most variable δ 13C among herbivores, though several other taxa are represented by single individuals, thus lacking dietary ranges. Among carnivores, Smilodon had the lowest δ13C values (-13.4‰) and Canis latrans the highest (-10.7‰). Carnivore δ 13C values only partially overlap the observed range of herbivore values suggesting that not all herbivores were consumed with the same frequency.;In comparison to Fairmead, δ13C values from McKittrick show a significant shift in isotopic values suggesting greater C4 plant availability from middle to late Pleistocene. Camelops showed the greatest shift towards C4 plants values, while Cervus had the most negative δ13C value indicating the presence of woodland C3 resources. Within the carnivore guild, Panthera and Arctodus had specialized diets trending towards forested habitats, while canids exhibit generalist diets.;Serially sampled teeth from both sites were used to investigate seasonality and temporal resource usage among megafauna. Equus from both localities showed little variation in δ13C, while at McKittrick Camelops diet included variable amounts of C 4 resources throughout a seasonal cycle. We also report the first ever serial sampled Tetrameryx tooth; δ13C variation throughout the tooth is low suggesting a stable diet. Comparing similarly aged inland McKittrick and coastal RLB faunas reveal significant differences (p<0.001). Bison, Equus (Feranec et al., 2009) and Panthera show statistically similar dietary δ13C while Camelops, Canis dirus, Canis latrans and Mammut show significant differences from previously reported RLB analogs (Coltrain et al., 2004).