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Humans’ Oldest Ancestor: Bag-Like, Microscopic Sea Creature

Meet your oldest ancestor: a bag-like, super-tiny creature of the sea. Wearing a big mouth on its elliptical body, it was a frightening little fellow. It has been documented in the journal Nature.

This is what your oldest ancestor looked like. The image is an artist’s rendition of the possible appearance of the creature which was no larger than a millimeter. Photo credits: S Conway Morris/ Jian Han.

You’re a Creature of the Ocean

Prepare to be horrified. Your oldest ancestor was no more than a millimeter in size. It resembled a sack more than it resembled you, and it came from the ocean. Such was the conclusion of a team of researchers who spotted microfossils of the minuscule sea creature in China’s Shaanxi Province. On the evolutionary timeline of humans, this prehistoric, microscopic child of the ocean would be at the earliest of events.

From Bag-Like Organism to Fish to Humans

Its story started around 540 million years ago. It constitutes a new species, and has been named Saccorhytus coronarius. Scientists think that it is the most primitive form of a deuterostome, a category based on its embryonic development, to which humans also belong. This makes of the Saccorhytus the ancestor of many other species.

“We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves. 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,” says one of the authors, Simon Conway Morris from the University of Cambridge.

It is said to provide invaluable information about the earliest stages of evolution of the species that allegedly developed into fish, and then into humans, explains co-author Degan Shu from Northwest University.

It Had a Mouth, But No Anus

The above picture was made after the well-preserved microfossils were analysed under an electron microscope, and with a CT scan. The features proposed by the scientists are in line with the assumptions made concerning primitive deuterostomes.

Based on the fossils, the scientists say that its body might have displayed bilateral symmetry, like humans do; its skin was thin and flexible; it might have some form of musculature that would have allowed it to contract and move. The team also believe that it might have had an evolutionary precursor of gills. It bore a mouth relatively big when compared to its body, and survived by engulfing food particles. However, it is not known if it had an anus.

Saccorhytus probably lived in between sand grains making up the seabed.

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