Abstract

Repeated joints are a hallmark feature of the tetrapod limb, and their patterning is a key step during limb development. Whilst the molecular regulation of joint formation is well-studied, we have an incomplete understanding of what controls the location, number and orientation (i.e. the pattern) of joints within each digit. Here, inspired by published gene expression profiles, we propose a dot-stripe mechanism for joint patterning, which comprises two coupled Turing systems. Our mathematical model can explain normal joint morphology in wildtype limbs, hyperphalangy in cetacean flippers, mutant phenotypes with misoriented joints and suggests a reinterpretation of polydactylous Ichthyosaur fins as a polygonal joint lattice. We extend our model to suggest that the insights from Turing-like dot-stripe models apply regardless of the biological specifics of the underlying mechanism, thus providing a unifying framework to understand autopodial joint patterning across the tetrapod lineage.