Underwater unknown

A strange honeycomb pattern appears on sea ridges around the world. We think that it is created by living creatures, but no-one has ever seen one. Oh, and there are fossils of the patterns going back 500 million years.

Hectonichus [CC BY-SA 4.0], via Wikimedia Commons
The pattern is known as Paleodictyon. It’s small, but not too small: individual hex shapes might be up to 3cm wide, and the repeated pattern can stretch over a metre. Various features suggest that it’s from a living creature of some kind rather than being a natural geological formation, but we have no idea what the creature is.

That hasn’t stopped scientists giving the creature a name: Paleodictyon nodosum. No-one has ever seen one – we only have the hexagonal patterns as proof that they exist at all. Some of the hypotheses about this mysterious animal:

1. It’s some kind of underwater worm that uses the honeycomb pattern to trap passing protozoa.

2. It’s the remains of the creature itself, like a dried-up sponge.

3. It’s the fossil of a body imprint: some giant thing brushed up against some mud and then swam off. This seems very unlikely.

The strangest thing is this: they also appear in the fossil record, going back as far as the Precambrian. That’s almost as far back as you can go, which means that if the first theory above is correct the Paleodictyon is one of the first structures ever created by a living being.

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