Fig. 6. Relationship between rate of oxygen consumption during burrowing (_O2b) and body mass for fossorial (filled circles) and semi-fossorial (open circles) mammals. Solid line is the phylogenetically correct regression relating _O2b to mass for fossorial species (_O2b=0.065M_b^0.98±0.06, where the mass exponent is mean ± s.e.). Inner dotted lines represent the 95% confidence interval of this regression; outer broken lines represent the 95% prediction interval. Data sources are provided in Table 1.