Animals with a front and a back
The first to crawl in a chosen direction
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Bilateral symmetry seems trivial until you consider what it implies: an axis means a front end, and a front end concentrates sense organs and nerve cells in one place. That is the origin of the head, and therefore of the brain. Kimberella from the White Sea is interpreted as an early mollusc relative, and the associated trace fossils show repeated, directional scrape marks. The trace fossil Treptichnus pedum, recording an animal burrowing systematically, is so characteristic that it is used to define the base of the Cambrian itself. Over 99 per cent of animal species today are bilaterians.
For children
By the White Sea in Russia lie fossils of a small oval animal called Kimberella — and beside it, scratches in the ancient sea floor where it scraped up food. It is the first animal we know of that had a front, a back, and could decide where to go.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org