Human forebear a bag-like beast with no anus: study

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Humans' earliest known relative was likely an egg-shaped creature that ate and expelled from the same gaping orifice some 540 million years ago, scientists reported Monday.

Startlingly well-preserved fossils of the tiny beast, dubbed Saccorhytus, were discovered in central China's Shaanxi province, they reported in the journal Nature.

Several major branches of evolution — one of them eventually leading to humans — began from this inconspicuous, sea-dwelling organism, they speculated.

"This may represent the primitive beginnings of a very diverse range of species, including ourselves," said co-author Simon Conway Morris, a professor at Britain's University of Cambridge.

A graph describing relations between Saccorhytus and other animals. /Nature

To the naked eye, the fossils look like black grains of sand.

"But under the microscope, the level of detail is jaw dropping," Morris said.

The sack-like animal's most distinctive feature is a large — relative to the rest of its body — mouth ringed by concentric circles of raised bumps. It probably ate by engulfing food particles and microscopic creatures.

Finding the creatures was not easy.

"We had to process enormous volumes of limestone -- about three tonnes -- to get to the fossils," said lead author Jian Han, a professor at Northwestern University in the city of Xian who made the discovery.

Once isolated, the samples were analysed with an electron microscope and a CT scan, allowing the team to build up an image of how the animal looked and lived.

(Source: AFP)