Locomotory adaptations in entoptychine gophers (Rodentia: Geomyidae) and the mosaic evolution of fossoriality

Pocket gophers (family Geomyidae) are the dominant burrowing rodents in North America today. Their fossil record is also incredibly rich; in particular, entoptychine gophers, a diverse extinct subfamily of the Geomyidae, are known from countless teeth and jaws from Oligocene and Miocene-aged deposits of the western United States and Mexico. Their postcranial remains, however, are much rarer and little studied. Yet, they offer the opportunity to investigate the locomotion of fossil gophers, shed light on the evolution of fossoriality, and enable ecomorphological comparisons with contemporaneous rodents. We present herein a quantitative study of the cranial and postcranial remains of eight different species of entoptychine gophers as well as many contemporary rodent species. We find a range of burrowing capabilities within Entoptychinae, including semifossorial scratch-digging animals and fossorial taxa with cranial adaptations to burrowing. Our results suggest the repeated evolution of chisel-tooth digging across genera. Comparisons between entoptychine gophers and contemporaneous rodent taxa show little ecomorphological overlap and suggest that the succession of burrowing rodent taxa on the landscape may have had more to do with habitat partitioning than competition.