540 million years ago, one of our ancient relatives lived between grains of sand on the bottom of the sea, wiggling around and engulfing food. It was a member of the “deuterostomes,” a group that includes everything from starfish and sea urchins, to monkeys and humans. The name means “mouth second,” to differentiate them from protostomes. During the embryonic stage, protostomes form their mouth first, and then anus, while with deuterostomes, it’s vice versa. Why is this group so diverse? What do they have in common? Whether it’s an eagle or an eel, their embryos all develop in the same way, with the anus forming first, followed by the mouth. After that, they branch off into four separate categories known as phyla. Humans belong to the Chordata.
The particular deuterostome newly-discovered in China, the teeny saccorhytus, is usually never fossilized. At the site in China, scientists found 45 of them in a layer of sedimentary rock. Their full name is saccorhytus coronarious, and they have a globular body like a bag and an unusually-large mouth. When they were alive, they would have likely possessed a thin, stretchy skin. It would have wiggled its way around its habitat by flexing its muscles. Its large mouth would have been used to swallow food. Oddly enough, it doesn’t appear to have an anus. Another unusual trait is that it has a set of what can only be described as the earliest form of gills, which would release the water the creature swallowed during feeding. Perhaps this is why it doesn’t need an anus.
Scientists say the creature most likely isn’t our direct ancestor, but it’s the closest we’ve ever seen. Having such well-preserved fossils means scientists can begin to understand more about the earliest evolution of a huge group that includes all the vertebras. Without fossils, it would be nearly impossible to picture what the common ancestor of a group that includes humans, starfish, and birds would look like. The group is so diverse, it’s like trying to solve a puzzle with a million pieces in every imaginable shade, and there’s no picture on the box. The more fossils scientists find, the more is added to the picture, so we start to get a better idea of how all the pieces fit together.
Why does any of this matter, really? Studying ancient fossils of microscopic squishies may seem like nothing more than a very specific waste of time, but mapping out the patterns of evolution can tell us about our future. Evolution hasn’t stopped occurring, and since it moves so slowly we can’t see it in real time, we have to look backwards. Figuring out how and why certain creatures and their traits evolved can help the human race spot anomalies caused by stuff like mutations and climate change, as well as cure diseases and make other advancements in biology. Knowledge is progress, and the saccorhytus fossil is another stepping stone.