You’ve probably heard that every bony land-dwelling creature on Earth evolved from fish
that grew limbs and crawled out of the water many million years ago.
可如今 海洋 湖泊 河流中超过99％的鱼
And yet, over 99% of the fish in today’s oceans, lakes, and rivers
have incredibly delicate fins, formed
by a series of spines covered by a thin web of skin.
It’s hard to imagine fins like those evolving into sturdy, weight-bearing limbs…
because they didn’t.
But the fins of a far more foreign fish did.
Very soon after bony fishes first evolved, they branched into two groups –
those with flimsy ray-type fins,
and those with more meaty appendages that were attached to
their bodies by a single strong bone.
At first, those so-called lobe-finned fishes far out numbered their ray-finned relatives,
but just as some of them were becoming adapted for life in the weedy shallows,
global climate fluctuations caused a mass extinction that devastated life in the oceans.
After the catastrophe, the ray-finned fishes recovered and took over the oceans.
The lobe-fins never recovered, but a few survivors
in the shallows managed to find their footing out of the water,
and eventually gave rise to every backboned, four-limbed creature to
ever walk, hop, crawl, or fly on land.
Hey, this is Emily.
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还可以在评论和我们互动 我们愿意倾听你们的声音 谢谢!
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