Biogeographic evolution of gadine codfishes

From an original area of endemism in the Northeast Atlantic (cf. Trisopterus) (green lines), gadine fish have spread to the western Atlantic (blue lines) and Arctic Ocean. Three species are endemic to the Pacific Ocean (red lines): Pacific tomcod (Microgadus proximus), Pacific codfish (Gadus macrocephalus), and Alaskan or walleye pollock (Theragra chalcogramma). The timing of the separation of the Pacific species from their respective closest relatives coincides with the opening of the Bering Strait, 3 ~ 4 Million Years Ago.  [Maximum likelihood analysis of 896bp of mitochondrial cytochrome b and cytochrome oxidase subunit I genes: molecular clock constraint enforced] (Figure 5 of Carr et al. 1999)