Figure 1.

Dlx genes are associated with morphological novelty in the vertebrate lineage. A cladogram depicting hypothesized phylogenetic relationships of extant lineages within the chordates. A partial listing of morphological characters supporting this phylogenetic hypothesis is shown. Asterisked characters are those that have been shown, in gnathostomes, to be associated with Dlx gene expression. Note that some analyses (12, 13) using molecular characteristics indicate that hagfish and lampreys are monophyletic (dashed line), suggesting that modern hagfish secondarily lost certain morphological characters. The position of neural crest and placodes is speculative because hagfish embryos have not been characterized. Cladogram and character list are derived from refs. 4 and 63.