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Fish invade the land

How did sea creatures manage to colonise the dry land?

The fossil record shows clearly that, as you might expect, it was a gradual process. And it was the ‘lobe-finned’ fish that did it.

The vast bulk of fish are ‘ray’ finned. They have the flimsy fins that we are familiar with – excellent for swimming with, but useless as legs.

But there are also these ‘lobe-finned’ fish. Their fins have bones in them. Lobe fins are much less good as paddles, which puts their owners at something of a disadvantage in open waters. Lobe-finned fish tend to frequent the shallow waters, bogs and tidal margins; which other fish keep away from.

Well before the land invasion occurred, some lobe-finned fishes had already acquired a limited ability to breathe air. This enabled them to survive in ‘anaerobic’ conditions that would kill other fish.

With their strong fins and ability to survive briefly out of the water, these fish became true masters of the marginal zone between wet water and dry land.

They still had to develop proper lungs, waterproof skins and so on. And the rest of the transition was neither easy nor quick. But perhaps it no longer appears as ‘impossible’ as it might have seemed before.