Quantitative data on bone vascular supply in lissamphibians: comparative and phylogenetic aspects

So far, studies documenting bone vascularization patterns have been mainly focused on amniotes. Lissamphibians, generally considered to have poorly vascularized to avascular bone cortices because of their low metabolic rates, have been largely overlooked, and no comparative dataset of bone vascularization exists for this group. To document this aspect of bone microstructure in urodeles and anurans, and to investigate the relationships between cortical vascular density, size, phylogeny and metabolic rate, we sampled 71 species (116 stylopodial elements) encompassing the taxonomic, body size and ecological diversity of the lissamphibians. Our results show that, with the exception of the largest taxon Andrias, extant urodeles have generally avascular limb bones; conversely, anurans can exhibit vascular density values equivalent to, or even higher than, those recorded in similar-sized lepidosaurs. Statistical analyses reveal that absolute cortical thickness in stylopod diaphyses is positively correlated to bone vascular density in lissamphibians. However, available data fail to clearly decipher the relationship between metabolism and bone vascularization. Finally, the present study underlines the existence of diverse, sometimes contradictory patterns, and highlights the complexity and multiplicity of the factors likely to influence bone vascular density.