Posted: Jun 30, 2011 2:53 am
susu.exp wrote:Ergo Proxy wrote:The reason that they both have prominent dorsal fins is because of convergent evolution. The dorsal fin is absolutely necessary for (large) sea creatures for stability
Ever looked at a beluga? Bowhead whale? Northern or Southern right whale dolphin? The Finless porpoise? Narwhal? North Pacific right whale?
All those have ancestors with dorsal fins.
It's certainly not needed for stability though. It just helps prevent some animals from rolling. Lots of cetaceans, belugas in particular, love to spin through the water and travel upsidedown anyways. It's super helpful too because when mammal eating orca are present they (and narhwals) can tuck themselves right up under the ice. Orca can't pursue them due to their dorsal fins forcing them to travel far deeper under the water.
The dorsal fin helps with sudden turns too. Most cetaceans just aren't great at turning quickly. Sharks, in general, are much better at it. Watching hammerheads turn is magnificent.
I watched a tagging operation of a big beautiful male beluga that absolutely broke my heart. Popping a couple holes through a dorsal fin to insert a tag is easy. Try doing that to someone with a dorsal ridge. It has far further to travel from one side to the other and is much deeper into the animal's back.
I spent the day with one of my favourite cetacean families so this is all very appropriate.