Bothersome burrowers: Tracking the impact of Botta’s pocket gopher (Thomomys bottae) bioturbation on a late-Holocene site

Abstract

Archaeological and paleontological research relies on the contextualization of artifacts and skeletal remains, but stratigraphic disturbances such as bioturbation can complicate temporal associations. More specifically, the mixing of fossil and subfossil material by pocket gophers (Thomomys spp.) may increase time-averaging, obscuring or even erasing stratification in terrestrial, open-air sites. Not only can bones be transported vertically by displacement of dirt by pocket gophers, but also the gophers themselves may die in their burrows, adding young skeletal remains to older deposits. Using a late-Holocene archaeological site in California as a case study, we establish the degree of bias introduced by native pocket gophers, Thomomys bottae, by radiocarbon-dating incisors of T. bottae and non-gopher small mammals from the same stratigraphic units. The ages of T. bottae incisors are younger overall, and span a wider age range, than the ages of other small mammals from the same sediment layers. Our data shows that a significant number of pocket gopher remains were introduced after the site’s deposition, and we conclude that this is a consequence of T. bottae burrowing. These results shed light on a common taphonomic process and may prompt reevaluation of faunal community reconstructions from fossil deposits impacted by pocket gophers and other fossorial mammals around the world.