Oldest bilateral embryos

This story, from February 1998, reports on fossil embryos 570,000,000 years old. They are microfossils–small balls of cells exquisitely preserved, from an era of sponges and sea anenomes. They appear to be early versions of organisms with right and left sides instead of radial, or no, symmetry.

Here’s a more scientific article on the microscopic fossil embryos, from the Proceedings of the National Academy of Sciences of the U.S.

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