TedStixon

Those bodies of water on the earth's surface with much higher salt content are invariably isolated lakes and inland seas that were formerly connected to the oceans in the distant past. Such high-salt lakes are the result of many millennia (even millions of years) of evaporation and reduction, which results in the nearby terrain becoming almost devoid of vegetation (due to the increasingly high alkalinity of the surrounding water table). So, you would expect to see near-desert-like conditions in the vicinity of isolated salt lakes and inland seas and virtually no large wildlife (except maybe migrating flamingos at certain times of the year). Point is, while there is evidence of "marine incursion" across the northern half of South America as far back as 14 million years ago (which did, in fact, produce the largest salt flats in the world at Uyuni, Bolivia), these salt lakes are very hostile and even toxic to complex life. Large animals, such as gill-people, simply couldn't have evolved there, with a saline content more than twice that of the ocean and virtually no food chain.

Charles Austin Miller