You're correct, the immediate ancestors of tetrapods almost certainly lived in freshwater, as known intermediate fossils like titaalik were found in fresh water

You're correct, the immediate ancestors of tetrapods almost certainly lived in freshwater, as known intermediate fossils like titaalik were found in fresh water stream deposits[1]. I believe all of the immediate ancestors of and early tetrapods have been found in fresh water deposits, although I can't confirm. [1] http://tiktaalik.uchicago.edu/searching4Tik3.html http://tiktaalik.uchicago.edu/searching4Tik3.html