2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 218-1
Presentation Time: 9:00 AM


TRAYLER, Robin B.1, DUNDAS, Robert G.2, FOX-DOBBS, Kena3 and VAN DE WATER, Peter K.2, (1)Department of Geosciences, Boise State University, 1910 University Drive, Boise, ID 83725, (2)Department of Earth & Environmental Sciences, California State University, Fresno, CA 93740, (3)Department of Geology, University of Puget Sound, 1500 N. Warner St, Tacoma, WA 98416-1048

Despite being the type fauna for the Irvingtonian North American Land Mammal Age, mammalian megafauna from Irvington remain under-studied. Stirton (1939) first reported vertebrate fossils from fluvial deposits at gravel quarries in the San Francisco Bay Area at Fremont, California. Subsequently, Savage (1951), Firby (1968) and Bell and Bever (2006) reported on the faunal assemblage which is represented by 54 taxa; 5 mollusks, 4 fish, 4 amphibians, 3 reptiles, 8 birds, 30 mammals. Other than the above taxonomic studies, no further research has been conducted on the fauna.

We use carbon (δ13C) and oxygen (δ18O) isotopes from tooth enamel to investigate the paleoecology of the Irvington megafauna. We sampled 24 individuals representing 10 taxa: Tetrameryx irvingtonensis, Camelops, Equus, Hemiauchenia, Mammuthus, Mammut, Arctodus, Canis dirus, Homotherium, and Panthera onca. Carbon isotope values range from -16.1‰ to -9.9‰. Mean δ13C values for carnivores and herbivores are -14.4‰ and -12.0‰, respectively. The Irvington fauna shows no statistically significant differences in δ13C values for taxa where n>1. (ANOVA, p > 0.1). For taxa represented by single individuals, only the δ13C value of Mammut fell beyond 1σ of all other taxa. δ18O values for the Irvington fauna range from 18.1‰ to 27.4‰ with a mean of 25.1‰. All δ13C values from Irvington are consistent with an environment dominated by C3vegetation.

Using enamel δ13C as a proxy for plant values (Kohn, 2010; Kohn and McKay, 2012), we modeled Mean Annual Precipitation (MAP). Modern MAP for Fremont, California is ~408 mm (Western Regional Climate Center, 2014) while modeled mid-Pleistocene MAP is a significantly higher at 901±219 mm.

Comparing the Irvington fauna to the similarly aged Fairmead Landfill locality (Trayler, 2012) reveals that Mammuthus, Camelops and Tetrameryx δ13C values differ significantly between the two sites (ANOVA, p < 0.05). Likewise, the Irvington Hemiauchenia value fell outside the 1σ range of the Fairmead population. These differences likely arise from the shift from a mixed woodland-grassland environment at coastal Irvington in the Bay Area to the more open prairie of Fairmead Landfill in the Central Valley of California.