Turnover in burrowing rodents: The roles of competition and habitat change

Changes in the burrowing herbivore fauna during the Cenozoic have led to the suggestion that competitive replacement was a driving force in the ecology and evolution of the burrowing herbivore guild. Alternatively, it has been proposed that differences in habitat preferences were associated with the expansion and contraction of the ranges of burrowing herbivores. We examine hypotheses of drivers of mammalian evolution in this guild by looking for evidence of apparent competitive replacements at a regional scale in the middle to late Miocene fossil record of the northern Great Basin. Mylagaulids are most common from 17.5 to 9 Ma, in the Hemingfordian through Clarendonian North American Land Mammal Ages and decline to extinction in the Hemphillian (9 to 5 Ma), at which time the family Geomyidae became more common in this region. In addition to observing this turnover within the guild, we find that geomyids and mylagaulids may occupy different habitats as indicated by evidence from mammalian assemblages and paleopedology. This suggests that mylagaulids and geomyids, rather than competing, may be tracking the extent of their preferred environment. We find no evidence for direct biotic interaction between the members of the guild and suggest instead that the changing abundance of mylagaulids and geomyids in Oregonʹs Miocene was shaped by habitat partitioning.