Figure 7

Theoretical tree of the relationships between extant gnathostomes and fossil species. The evolutionary scenario described in the discussion is illustrated, including the diversification of vertebrate odontodes and hypotheses for the modification of Dlx gene expression patterns over time: a- proposed ancestral situation (note that the early Dlx2 mesenchymal expression depends on the alternative hypotheses in c); b- loss of epithelial Dlx3 and Dlx5 expression; c- two equi-parsimonious hypotheses: c1 = gain in bony fish/c2 = loss in chondrichthyans of the Dlx2 early mesenchymal expression; d- loss of Dlx2 expression in teeth but not in dermal denticles.