Members of HOX linked gene families that have arisen early in vertebrate history. Order of branching within phylogenetic trees was used to estimate the time windows (double headed arrows on the right) of gene duplication events relative to major cladogenetic events. For each family the lower limit of time window was defined from fish-tetrapod split and the upper limit from the branching order of available closest invertebrate ancestral sequence (Protostomes: Drosophila, Apis mellifera; Echinoderm: Sea Urchin; Cephalochordates: Amphioxus; Urchordate: Ciona intestinalis, Ciona savignyi). The INHBE, INHBC and SLC4A8, SLC4A10 genes arose after the fish-tetrapods split. Previously Proposed timing [3-6] of extensive gene duplications during early chordate evolution is given on the left of the diagram.