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Reply	auntiegrav says: My suspicion is that it was a shallow water environment, and the animals that spent the least amount of time and the smallest surface exposure were less likely to be caught by a wading predator that detected surface disturbance. Much like why a submarine has a periscope.Any paleontologists out there?  (no votes) Tags: unanswered, domestic science, animals, human body.
	posted on 2008-07-03 21:23:00 | Report abuse

Reply	Norman says: Good question - seals and otters (and manatees?) don't have blow holes, or show any sign of their nostrils migrating.They're all smaller than whales and dolphins - is that significant? A different lifestyle?  (no votes) Tags: unanswered, domestic science, animals, human body.
	posted on 2008-07-04 15:44:00 | Report abuse

Reply	Nick says: I am no expert but I would suspect it reflects a period in which an ancestral species lurked in shallow coastal lagoons or along riverbanks and the evolution of the upper blowhole allowed it to remain hidden.Probably a lifestyle broadly similar to that of alligators and crocodiles today.  (no votes) Tags: unanswered, domestic science, animals, human body.
	posted on 2008-07-06 13:42:00 | Report abuse

Reply	MacLir says: While I would have to check references to be certain, I recall that the three groups in question are adapted in the degree that they have spent as aquatic species; i.e. cetaceans longest, sirenians next, and pinnipeds last.It is notable that the sirenians closest land relative swims quite well, but largely underwater, with it's nostrils elevated above the surface on it's own snorkel.  (no votes) Tags: unanswered, domestic science, animals, human body.
	posted on 2008-07-08 23:06:00 | Report abuse

Reply	maclir1 says: To address your comment from another perspective, the blowholes are nostril(s) that have migrated up and back.Reconstructions of transitional ancestors of whales somewhat resembled crocodilians in general body plan, but evolution took a different turn with them as they went to fully aquatic life cycles. A "top-mounted" blowhole puts the intake both at the highest point of a resting cetacean and away from the pressure wave at the rostrum as they move at speed.The elongated nasal passages / sinuses which trace out the phylogenetic journey of the whale's "nose" are put to use as noise producers; whale songs have less in common with Maria Callas than they do with the C-minor chord your Grampa makes when he blows his nose. :-D  (no votes) Tags: unanswered, domestic science, animals, human body.
	posted on 2008-07-08 23:25:00 | Report abuse

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