Understanding the taphonomic biases affecting fossil deposits is necessary in order to extract their true ecological signals. In terrestrial sites, the mixing of fossil material by mammalian bioturbators can substantially increase time-averaging, obscuring or even erasing stratification. In particular, pocket gophers (Thomomys sp.) are known to burrow in Holocene sites and thereby complicate the contextualization of faunal remains. Not only is it unclear if bones have been transported vertically by gophers, but the gophers themselves have the potential to die in their burrows, adding young skeletal remains to older deposits. We establish the degree of bias introduced by gopher remains in a late-Holocene archaeological site in Woodside, California by radiocarbon dating skeletal remains of Thomomys bottae and non-fossorial small mammals from the same stratigraphic units. The ages of T. bottae bones are younger overall, and span a wider range, than the distribution of ages from other small mammals from the same site and sediment layers. This suggests that a significant number of gopher remains have been introduced after the site’s deposition as a consequence of burrowing. These results shed light on a common taphonomic process that affects archaeological and paleontological sites, and may prompt reevaluation of faunal community reconstructions from fossil deposits impacted by gophers and other fossorial mammals.
Plains pocket gopher, Geomys bursarius, a grassland inhabitant, is common among the mammal taxa identified on the southeast Ozark margin at the Lepold site, 23RI59, Ripley County, Missouri. Its presence throughout the midden depth, whether an incidental inclusion or human prey, implies that a favorable habitat existed in the immediate vicinity. As radiocarbon dates indicate midden deposition began about 7500 radiocarbon years before present, grassland was a component of the local vegetation beginning in the middle Holocene, if not before.
Bothersome burrowers: tracking gopher (Thomomys bottae) time-averaging in a late-Holocene site in California
