Evolution of bone microanatomy of the tetrapod tibia and its use in palaeobiological inference.

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 <or= 0.005) relationship between long-bone microanatomy and habitat. Randomization tests reveal a highly significant (P <or= 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.