Image: S Conway Morris / Jian Han

Here’s a joke for you: What has one horrible mouth and no butt? Your great-great-great-great-great-(etc.) grandpa, probably.

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Chinese researchers have collected dozens of these tiny sea creature fossils, called Saccorhytus coronarius and over 500 million years old, in South China. They think the newly-discovered critters predate the earliest deuterostomes, animals that grow two openings early in their embryonic development, just like us. A creature just like it could be our distant ancestor, and in fact, the ancestor of all other deuterostomes, from earthworms to dolphins.

“These fossils throw new light on what appears to be an early stage in deuterostome evolution,” the researchers write in the paper published today in Nature.

Image: Jian Han

The study describes this creature as bag-like, measuring around 1.3 by 0.8 millimeters, with a large main opening and eight tiny body cones, and again, with apparently no anus (though maybe the researchers just haven’t spotted it). So we shall call it the buttless bagbaby, for now. The scientists suggest its structure allowed it to ingest seawater and food together, exhale the water through the cones, and let out waste material through holes in its body.

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Researchers are perhaps most excited that creatures like the buttless bagbaby could explain one major conundrum in animal development. There’s a big gap in the fossil record right around where animals should have developed, study co-author Simon Conway Morris, a professor of palaeobiology at the University of Cambridge, explained to The Guardian. Perhaps the earliest animals were simply too small and could only fossilize under certain circumstances, though this is speculative.

So, while some may be harping on our differences, it’s worth remembering that deep down, we’re all the same. A long time ago, we were all just buttless bagbabies.

[Nature]