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Your family tree begins with this ugly wrinkled sea sack

Can you see the family resemblance?

Artist's reconstruction of Saccorhytus coronarius.

University of Cambridge

If you didn't like the (erroneous) idea that humanity descended from apes, you're going to hate this one. Scientists have found what they think is humanity's earliest known ancestor, and the family resemblance is striking.

The newly discovered microscopic organism, found in China, has been called Saccorhytus coronaries. This is because it looks like a sack, is about a millimetre in length, with an elliptical body and a large mouth at one end.

It's believed that the new species, around 540 million years old from the Cambrian Period, is the most primitive example found to date of the superphylum known as deuterostomes, most of which are from 510 to 520 million years ago. This category is very broad, covering vertebrates, starfish and other five-pointed marine animals, and acorn worms and graptolites.

So while it's true that Saccorhytus could have been a human ancestor, according to the study, published today in the journal Nature, it's a common ancestor for a huge range of species, perhaps not ground zero but certainly a critical link.

"We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves," said Simon Conway Morris, Professor of Evolutionary Palaeobiology and a Fellow of St John's College at the University of Cambridge.

"To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail is jaw-dropping. All deuterostomes had a common ancestor, and we think that is what we are looking at here."

University of Cambridge

The researchers believe that Saccorhytus may be something of a "missing link" in the molecular clock, a technique that uses the mutation rate of biomolecules to predict when two or more life forms diverged from a common ancestor. However, at some point before Saccorhytus' lifetime, there are hardly any fossils to match the clock. One theory is that the creatures were simply too small for fossils -- and the size of Saccorhytus is consistent with this theory.

Thanks to electron microscopy and CT scanning, these microfossils were able to tell us a lot about our tiny early forebears.

The region in which it lived would have been a shallow sea, and it was so tiny it probably lived between grains of sand, the researchers ascertained. Its body was bilaterally symmetrical and covered with thin, flexible skin, which suggests it also had muscles of some sort and was able to wriggle about.

Its most prominent feature was its large, gaping mouth, which it probably used to engulf food particles whole, and the small conical structures that you see in the image above could have allowed water to escape, like very early gills.

However, the researchers couldn't find an anus.

"If that was the case, then any waste material would simply have been taken out back through the mouth, which from our perspective sounds rather unappealing," Conway Morris said.

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