A volcanic-island model for the origin of the seal and other marine mammals


Allan Krill
3/15/21  

From genetic evidence it is thought that the first seals evolved about 23 million years ago, near the beginning of the Miocene epoch. A simple model for the evolution of seals is that mammals resembling dogs, bears, and weasels accidentally rafted to oceanic volcanic islands that eventually sank out of sight. 

Erosion acts on rocks that are exposed above sea level. After the last active volcano of an oceanic island becomes extinct, erosion can remove the mountain and reduce it to a low flat-topped island. Erosion mostly stops at sea-level, but subsidence continues. Cooling and contraction of the mantle beneath the ocean floor cause oceanic islands to sink a thousand or more meters over a time span of tens of millions of years. A flat-topped undersea mountain is called a guyot, and there are 283 known guyots in the world's oceans. 

Considering the models for the Galapagos marine iguana, and for Bioko chimps, this model of sinking oceanic volcanic islands seems likely for seals, and for other aquatic mammals. But I have not found mention of such models on the internet. 

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