Bone microanatomy appears to track changes in various physiological or ecological properties of the individual or the taxon. Analyses of sections of the tibia of 99 taxa show a highly significant (P ≤ 0.005) relationship between long-bone microanatomy and habitat. Randomization tests reveal a highly significant (P ≤ 0.005) phylogenetic signal on several compactness profile parameters and lifestyle. Discriminant analyses yield an inference model which has a success rate of 63% when lifestyle is coded into three states (aquatic, amphibious and terrestrial) or 83% for a binary model (aquatic vs. amphibious to terrestrial). Lifestyle is inferred to have been terrestrial for the stem-tetrapod Discosauriscus (Early Permian), the basal synapsid Dimetrodon (Early Permian), the dicynodont therapsid Dicynodon (Late Permian), an unindentified gorgonopsian (Late Permian); the parareptile Pareiasaurus (Middle or Late Permian) is modelled as being aquatic, but was more likely amphibious.