FIGURE 8. Summary of the evolutionary relationships between selected patterns of granule cell development in vertebrate cerebellum.

On the left, a simple phylogenetic tree of vertebrates is contrasted with the distribution of granule cells (brown) in adult cerebellum seen in schematic transverse section (Nieuwenhuys et al., 1998). All jawed vertebrates display a distinct cerebellum containing granule and Purkinje cells. The status of the cerebellum in the jawless lamprey (top) is less clear. To the right, the proposed developmental relationships between granule cell precursors (yellow) and definitive granule neurons are shown in schematic dorsal views for the shark (a), teleost (b) and bird or mammal (c). Our results suggest that an EGL is likely to have evolved as a developmental strategy after with the emergence of amniotes (black dot).