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Re: On the subject of mysterious absences...The Answer

Briefly: if you want to filter feed without gills,

Of course, there's always *Leedsichthys*, the Jurassic pachycormiform teleost that reached whale dimensions and was a filter-feeder.

you need to take in a large amount of water and then somehow stop it going down your gullet before you spit it out past filtering surfaces such as baleen . Only mammals can do this, as only they have seals that shut off the back of the throat (such as you use when you gargle) -- probably evolved in association with suckling."

Don't crocodiles have the same?

On the other hand, most of today's baleen whales live in cold water that simply didn't exist before the Oligocene...