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onioning t1_j117x28 wrote

Reply to comment by Ruuhkatukka in TIL Lake Baikal is located in southeast Siberia and is the oldest and deepest lake in the world, at 25 million years old and 1,700 meters deep. It contains 20% of the world's unfrozen freshwater and is home to a rich and unusual freshwater fauna that is of significant value to evolutionary science. by wisely_lined56

This is all speculation. Just perhaps the most plausible explanation. There's literally no evidence of river going seals up there. Though that doesn't at all mean it didn't happen. Finding a river going ancestor somewhere would change things, but the fossil record can be really cruel sometimes.

If they came from the West this problem doesn't exist, because that would be a voyage of shorter rivers between larger bodies of water.

There's a good YouTube video on this. Can't recall if it's PBS or Moth Light Media or someone else, but details the various theories.

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