INFLUENCE OF HABITAT AND SOIL TYPE ON THE EVOLUTION OF BURROWING IN MAMMALS

Burrowing behavior (fossoriality) has evolved repeatedly in a variety of animals, vertebrate and invertebrate, aquatic and terrestrial. This repeated evolution has led to widespread convergence in morphology, ecology, and behavior between independently evolved groups of burrowing animals. One of the major causes hypothesized to drive the evolution of burrowing is environmental change, specifically toward more open habitats. It has been shown in the past that different soil characteristics have a significant impact on the energetics of digging; however, the influence of substrate on the course of morphological evolution of burrowers remains relatively unstudied. This study aims to determine whether there is evidence for an influence of digging substrate on the evolution of digging. Additionally, this study looks for an influence of substrate on the method of digging (scratch, head-lift, incisor, or humeral rotation) evolved. Results show that the most behaviorally derived burrowing mammals inhabit soft, dry, sandy soils, which are the easiest to break up and move through, although they may make it more difficult to maintain extensive burrow systems. However, burrowing mammals, even subterranean species such as moles, inhabit a variety of different soil types and habitats. There is, however, some evidence that the morphology and behavior required to dig in more compact or rocky soils is recognizably different from that used in softer soils. Consideration of phylogenetic relationships among diggers, as well as the fossil record of fossorial animals, suggests that digging evolves most commonly in open habitats with relatively dry soils, but that it has evolved in a few mammals living in more forested habitats with harder soils, illustrating the evolutionary drive that has created such widespread convergence in this life habit.