how did some freshwater fish like sturgeon end up in far-apart places (like the Great Lakes and Caspian Sea, for sturgeon) with no fresh-water path between them?

Question

how did some freshwater fish like sturgeon end up in far-apart places (like the Great Lakes and Caspian Sea, for sturgeon) with no fresh-water path between them?

In: 1

Answer 1

There used to be water paths between them. The oceans were higher. The Midwest US used to be under a warm shallow sea, it’s all limestone here. To my knowledge, the Great Lakes are what’s left, but now fresh water.