“Oldest Known Human Ancestor” –Revealed by Discovery in Central China of Microscopic Sea Fossil

 

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"To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail was jaw-dropping, " Simon Conway Morris, from the University of Cambridge told BBC News. "We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves. All deuterostomes had a common ancestor, and we think that is what we are looking at here."


Fossilized traces discovered in Central China of a 540-million-year-old "exquisitely well preserved"
microscopic sea animal is the earliest known step on the evolutionary path that led to fish and – eventually – to humans, according to Nature journal. The research team says that Saccorhytus is the most primitive example of a category of animals called "deuterostomes" which are common ancestors of a broad range of species, including vertebrates (backboned animals).

 

Saccorhytus, which moved by wriggling, was covered with a thin, relatively flexible skin and muscles was about a millimeter in size, and is thought to have lived between grains of sand on the sea bed. The researchers were unable to find any evidence that the animal had an anus, which suggests that it consumed food and excreted from the same orifice.

The study was carried out by an international team of researchers, from the UK, China and Germany.
Degan Shu, from Northwest University in Xi'An, Shaanxi Province, where the fossils were found, said: "Saccorhytus now gives us remarkable insights into the very first stages of the evolution of a group that led to the fish, and ultimately, to us."

Until now, the deuterostome groups discovered were from between 510 to 520 million years ago. These had already begun to diversify into not just the vertebrates, the group to which we and our ancestors belong and animals such as starfish and sea urchins. The research suggests that the creature had a large mouth, relative to the rest of its body, and probably ate by engulfing food particles, or even other creatures.

 

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Its body was symmetrical, a characteristic inherited by many of its evolutionary descendants, including humans. Conical structures on its body suggest a very early version of gills.

“These are, we suggest, the precursors of what we call the gill slits which you see in a fish,” he said. The role of small pores across the body, Morris adds, is more of a mystery, although he suggests that they might have been involved in securing the animal to sand grains, possible by releasing some sort of adhesive, or may otherwise have played a sensory role.

“These are really interesting and to my mind surprising fossils,” said Imran Rahman, museum research fellow at the Oxford University Museum of Natural History and an expert in the field. “[They have the] potential to greatly improve our understanding of the early evolution of deuterostomes, which is the major group to which vertebrates – including humans – belong, so they are obviously going to be important going forwards for understanding our evolutionary history.”

The tiny size of the fossils, Rahman adds, is particularly remarkable, noting that previously discovered fossils of younger deuterostomes are often several centimetres in length. “That kind of opens up the tantalising prospect that maybe some of these oldest animals were really microscopic as well,” he said.

Conway Morris, that the discovery could shed light on an enduring conundrum: why there is an apparent blank in the fossil record from around the time that animals are thought to have emerged based on the so-called “molecular clock” – an approach that estimates the dates of evolutionary splits from the rate at which genetic differences accumulate. “If indeed the first of these animals including Saccorhytus were very, very tiny, they could only preserve in very, very exceptional circumstances – they basically slip through the fossilisation net,” said Conway Morris.

While Conway Morris admits the idea is speculative, the latest discovery, he says, makes it an intriguing possibility.

“The question here of course is: "is it possible that there is a deep cryptic history that has almost entirely eluded discovery because these things are absolutely tiny?”

The Daily Galaxy via BBC News and theguardian.com

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