Fig. 2

Anatomical and morphological features seen in organisms bear witness to the activity of specific regulatory modules. Studies of living organisms can identify the regulatory entities of specific developmental processes, which produce well-defined phenotypic traits. Such phenotypic traits, thus, represent structural fingerprints of the deployment of those developmental regulators. In turn, identification of structural fingerprints in fossils provides evidence for the activity of their corresponding regulatory entities in extinct lineages, informing the evolutionary history of those regulators