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

[David Marjanovic <david.marjanovic@gmx.at>]

>  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...