Fig. 5.

Parallel evolution of neuronal centralization in the animal kingdom. The diagram summarizes the current view of evolutionary relationships in the animal kingdom and indicates the presence or absence of a central nervous system (CNS) or brain. From this tree it is possible to see at least 9 possible events of multiple origins of complex brains – shown as red numbers. Circles indicate possible events of multiple origins of neurons. See text for details. This reconstruction of phylogenetic relationships among phyla is a combined view based upon recent large-scale molecular/phylogenomic analyses of several dozen proteins from representatives of more than 15 animal phyla [20, 24, 31, 34, 47, 63, 64, 78, 82, 87]. Only representative groups of the 36 known animal phyla are shown in the diagram. The origin of animals can be traced back to more than 700 Million years ago (Mya) [24]. However, the extant animal phyla might have a more recent evolutionary history and the diversification of the modern bilaterian phyla might be linked to the cambrian explosion. As a result the accurate evolutionary relationships among basal lineages and major bilaterian phyla are not well resolved (dotted lines). Possible timing of the divergence in the diagram is indicated as Mya