Biologists aren't entirely sure which creature modern cetaceans (dolphins, whales, and porpoises) are descended from. The traditional theory suggests mesonychids, an extinct order of carnivorous ungulates (hoofed animals) which resembled wolves. But more recent genetic analysis points to artiodactyls, a hippo-like creature. Regardless, all cetaceans were land mammals at one point in their evolutionary history — and they had to undergo some rather remarkable changes to adapt to underwater life.
Recently, researchers from Korea Institute of Ocean Science and Technology, Korea Genome Research Foundation, BGI, and other institutes, performed a comprehensive analysis of the genomes of several cetaceans, including the minke whale, fin whale, bottlenose dolphin, and a finless porpoise. They did so to improve their understanding of the evolutionary changes required for terrestrial mammals to adapt to the ocean — but at the level of the genome.Lack of Oxygen, Excess Salt
First and foremost, the adaptation to ocean life was marked by resistance to physiological stresses caused by a lack of oxygen and high salt levels. The researchers were able to identify several whale-specific genes strongly associated with these crucial adaptations, including the peroxiredoxin (PRDX) family, O-linked N-acetylglucosaminylation (O-GlcNAcylation). Basically, adaptations to the water favored those mutations that were associated with stress-responsive proteins and anaerobic metabolism.