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> From: scuba <scuba@uc*.be*.ed*> wrote on Thu 7 Jul 1994 03:31:04 >-0700 (Subject: Old News On Ecology & Nature):- > > > I post collections of news stories that I think may interest divers ... > > Second..ANCIENT WALKING WHALES... > It may have taken whales a long time to >evolve their peculiar brain neuroanatomy and function that lets them live >without needing REM sleep (= dreaming, which can't happen safely in water). >Before that, they had to haul out sometimes to catch up with their need for >REM sleep, and the long thin shape was to let them move about ashore >easier. A fully grown Basilosaurus hauling out must have been quite a sight! Actually, dreaming can happen underwater. I am not sure about the larger Cetaceans such as whales, but dolphins sleep/dream with one hemisphere at a time, switching their "sleeping" sides of the brain during their sleep cycle. While doing this some species swim in complete defensive head to tail circles of about 6 animals, starting say - clockwise - first, watching out for danger, ec. with their left eye, and thus right brain, and resting their left brain. They periodically switch rotational direction durring their sleep - circling counterclockwise (anticlockwise to you Brits) for awhile sleeping on the other side of the brain. Some Cetacean Neurobiology: Evolution: Our human brain size tripled from approx. 450cc 5 million years ago, to 1700 cc 1 million years ago. The dolphin brain size began increasing 50 million years ago, from 700 cc to the 1600 cc in Tursops approx 30 million years ago. Dolphins have been evolving approx. 29 million years longer than we have. Neocortical (= new cortex - complex multisensory brain areas used for perception and abstract thought) Limbic (ancient cortex - "primitive" brain areas for basic memory, emotions, instinctual responses) Dolphins have a greater neocortical-limbic ratio than humans. They, however, have only two distinct layers of neocortex, while we have six neocortical layers. This is part of their distinct evolutionary lineage - they are one of the most specialized mammalian orders, but what it means functionally is unclear. The cephalization coefficient - the ration of brain size to body size - is approximately the same for man and Cetacean. Mark "Diviner than dolphin is nothing yet created" - Greek poet Oppion
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