Skull developmental modularity: a view from a single bone - or two

I review recent studies that connect development and evolution of skull bones in teleosts. Development uses genetic information to build a structured, modular phenotype, and since selection acts on the phenotype, developmental modularity may influence evolvability. Just how is a complex developing morphology spatially partitioned into modules? Here I briefly examine cellular, molecular genetic, and multivariate statistical approaches to the identification of developmental modules. Furthermore I review our evidence that developmental modularity provides evolutionarily labile regions within the skull and hence potentially biases evolutionary change in a positive manner. This view is rather different from early ones in the field of evolutionary developmental biology, in which developmental constraint due to patterns such as heterochronies were supposed to negatively impact evolution.