Bag-Like, Big-Mouthed Sea Creature Could Be Earliest Human Ancestor

This minute wriggly sea blob could represent some of the earliest steps along the path of evolution

mouth bag
An artist's recreation of what the ancient creature looked like. Jian Han

Researchers have discovered fossilized traces of they believe to be humans’ earliest-known ancestor: a tiny, wriggly, sea-dwelling blob that may have pooped through its mouth.

Such early steps in evolution are rarely preserved in the fossil record—the delicate structures commonly breaking down over time. But a team of researchers from China and Germany came across just such a cache of fossils in Shaanxi Province of China, according to a press release from the University of Cambridge.

No larger than a millimeter, the creatures likely slithered through the sandy bottoms of the shallow seas some 540 million years ago, Nicholas Wade reports for the New York Times. Researchers dubbed the little creature Saccorhytus, after its “sack-like features,” documenting the oddball in a recent study published in the journal Nature.

The Saccorhytus is thought to be the oldest-known example of a “deuterostome”— an ancient biological class that is ancestral to many animals, including people. Other deuterostome groups familiar to scientists lived 510 to 520 million years ago, and had already began to diversify into different species.

The Saccorhytus may represent “the primitive beginnings of a very diverse range of species, including ourselves,” Simon Conway Morris, Professor of Evolutionary Palaeobiology and a Fellow of St John’s College, University of Cambridge, says in the release.

By studying the minute fossils using an electron microscope and CT scanner, researchers were able to create a picture of what this creature may have looked like. And the results are the stuff of monster movies. The creature likely sported a large, gaping mouth and was covered in a film of thin skin. It also had some form of musculature, and likely got about by wriggling.

There was something else rather unusual about the Saccorhytus. As Wade explains, it does not appear to have had an anus. If this is in fact the case—the fossilized material was somewhat crushed, making microscopic posteriors difficult to find—waste would have been secreted through the Saccorhytus’s mouth.

Scientists’ reconstructions yielded other interesting finds. According to the BBC, the Saccorhytus had conical structures on its body, which may be an evolutionary precursor to gills.  The creature’s body was also symmetrical—one of the few traits humans still share with this eccentric ancient life.

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