Developmental evolution of metazoan bodyplans: the fossil evidence.

Evidence from the fossil record, developmental biology and metazoan phylogeny demonstrates that the rapid origination of major metazoan bodyplans during the late Neoproterozoic and earliest Cambrian was intimately associated with a series of innovations in developmental control mechanisms that included the Hox gene cluster. The interval between about 565 Ma (million years ago) and 530 Ma evidently includes the protostome-deuterostome branching, diversification of independent higher metazoan clades, diversification of important developmental control systems, and formation of higher metazoan bodyplans. Comparative paleontological and developmental studies will allow further tests of alternative models for the sequence of these events, illuminating the association between developmental and bodyplan evolution.