Whether you love spiders or can't be within 10 feet of them, you probably think of them crawling around on land. Historically, most researchers would probably say the same thing: Based on the fossil record, they've thought the earliest arachnid ancestors existed around 450 million years ago, living and diversifying exclusively on land. But a new study out this week in the journal Current Biology suggests arachnid brains may have originated much earlier in the ocean.

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