Figure 7

A chronological correlation of paleoceanographic events and the phylogeographic histories of the dusky dolphin and anchovy ( Engraulis sp). Above the timeline are paleoceanographic events, with the point estimates and range of dates for each event. EEP = Eastern Equatorial Pacific; SM = Strait of Magellan. Below the timeline are events in the history of anchovy and dusky dolphin populations. Bars represent 95% confidence intervals for point estimates, indicated by black arrows. At least as early as 4.3 mya, a cooling trend began in the Eastern Equatorial Pacific (EEP), causing sea surface temperatures in this tropical region to drop from 26°C to as low as 20°C in the late Pleistocene [51]. This drop in temperature caused a peak in primary productivity 2.9 mya that was 2 to 3 times greater than average values earlier in the Plio-Pleistocene [51]. At 1.6 mya, this productivity began to decline as sea surface temperatures began to rise [51]. As warmer tropical waters returned, the range and abundance of anchovy in the EEP would have declined, resulting in the gradual disappearance of this dispersal corridor, consequently resulting in an anti-tropical division of dolphin populations.