Conclusions:
Much progress has been made in recent years towards understanding chondrichthyan evolution and ecology. However, it is undeniable that many major knowledge gaps remain, and in particular our understanding of trait evolution in this clade is less robust than in many other vertebrate radiations. I argue that the key driver of this uncertainty is a lack of integration between genetic, morphological, and behavioural studies. Failure to integrate these key areas of organismal biology fundamentally constrains our understanding of phenotypic evolution, both past and present. Most significantly, this impedes study of the genetic architectures underlying phenotype and how selection acts upon them. Despite this, the necessary tools to overcome this major limitation already exist and have been applied to other taxa (Figure 1). Future studies should focus on increasing the taxonomic breadth of existing studies of chondrichthyan genetics, morphology, and behaviour, as well as the implementation of more quantitative genetic approaches. Only though this will we truly be able to understand trait evolution in Chondrichthyes to a comparable extent to other major vertebrate radiations, and its implications for past evolution and vulnerability in the face of climate change.