Claims about cetaceans (speculative)

…cetacean brain size, relative to body size, increased substantially about thirty-eight mill years ago when the odontocetes evolved from the ancient archaeocetes…

What drove these changes? It does not seem to have been the transition to an aquatic existence itself as that occurred about fifty-five million years ago and brains stayed at roughly the same relatively small size relative to body weigt as the archaeocetes made their gradual entry into the ocean.  A better hypothesis is that the increased brain size of the odontocetes thirty-eight million years ago was driven by the evolution of echolocation.  The early odontocetes had inner ear bones that were good at picking up high frequency sound, which suggests that they had developed a form of sonar.  Lori Marino thinks “that echolocation came on line and then got co-opted for social communicative purposes.”  In this scenario, the odontocete brains increased in relative size to deal with the acoustic information itself, as well as, perhaps, a new perceptual system based on the data from the returning echoes.  But…the change may have been even more profound: “This may indicate that the large brains of early odontocetes were used, at least partly, for processing this entirely new sensory mode [echolocation] that evolved at the same time as these anatomical changes and perhaps for integrating this new mode into an increasingly complex behavioral ecological system.”

That is from the new and notable The Cultural Lives of Whales and Dolphins, by Hal Whitehead and Luke Rendell, previously covered on MR here.  And here is my earlier post on the economics of dolphins.


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