Re: Why do mammels like a dolphin move there tail up and down.

Why do mammels like a dolphin move there tail up and down? Fish like sharks move there tail sideways. Is there a relation to breathing air?

Shark	Ichthyosaur	Dolphin

Other marine animals, all of which breathe air, have "sideways" tails: crocodiles, sea snakes, otters; ichthyosaurs and mososaurs also had "sideways" tails. For that matter, flying fish, which spend a good bit of time above the surface, have "sideways" tails too, and they don't seem to have any problem getting to the surface or sculling across it.

On the other hand, pinnipeds -- seals, sea lions and walruses -- use their hind feet as "up-and-down" tails when swimming; given the recent discoveries of proto-whales with very long hind legs, I'd bet that this is the origin of the up-and-down tails of cetaceans.

Here are some links:

• Jaap's Marine Mammal Pages contains information on whales, dolphins and pinnipeds. Jaap van der Toorn is the author of the FAQ for alt.animals.dolphins.
• Ian Geraint Jones' Shark site is quite comprehensive.
• Ichthyosaurs:
  • There is an ichthyosaur exhibit at The Museon in The Hague; I'd have included a link but it is a bit unorganized. Try a Yahoo search.
  • One of the most famous ichthyosaur finds, which established the truly marine character of the reptile, is in Glasgow's Hunterian Museum.

NOTE: I was unable to find any web sites with information on the long-legged proto-whales, but an article appeared in Science magazine a few years ago -- before April 1995, that's the limit of the online index.

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