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Ancient Bag-Like Sea Creature Could Be Oldest Human Ancestor

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A bag-like marine creature from China could be human's earliest relative.

In a study published on Jan. 30, scientists revealed that the sea creature that wriggled in seabed mud about 540 million years ago could be the earliest known animal in the evolutionary branch that eventually led to humans.

Evolutionary Deeper Ancestors

Apes and monkeys are known to have evolutionary links with humans, who emerged 200,000 years ago, but paleontologist Simon Conway Morris, from the University of Cambridge, explained that humans have a series of evolutionary deeper ancestors than these primates.

Cambrian Period Creature

The creature called Saccorhytus coronaries, whose name means wrinkled sack, is an example of an ancient human relative. It lived during the Cambrian Period, the time of exceptional evolutionary experimentation when life experienced great increase in diversity. Creatures that emerged during this period include penis worms with teeth and crustacean-like animals. It was the time in history when the food chains were just beginning to assemble.

"It was the beginning for the world as we know it now, a world that's dominated by active animals — things walking around, swimming around, not just sitting there," said paleobiologist Peter Van Roy, from Yale University who was not involved in the study.

Most Primitive Member Of Deuterostomes

Saccorhytus, which has an oval body and a relatively big mouth for its size of about 1 millimeter, appears to be the most primitive member of the broad animal group known as deuterostomes, which include vertebrates such as reptiles, birds, fish, amphibians and mammals including humans.

Animals known as echinoderms, which include sea urchins and starfish, as well as the hemichordates, which include acorn worms, also belong to this group.

"We think that as an early deuterostome, this may represent the primitive beginnings of a very diverse range of species, including ourselves," Morris explained.

Characteristics Of Saccorhytus Coronaries

Researchers used computed tomography scan and electron microscope to construct image of the ancient creature.

Analysis of the creature's fossil revealed that it had a bilaterally symmetrical body, a characteristic passed down to its descendants including humans. It was also covered with a thin and flexible skin that hint it had some kind of muscles that may have helped it wriggle around in the water.

The small, conical structures that encircle its mouth may have also allowed the water it swallowed to escape from its body. These structures were possibly the precursor of gill slits that are found in fish, the vanguard of vertebrates that appeared about 10 to 15 million years after the Saccorhytus.

Paleontologist Degan Shu, from China's Northwest University, said that the creature, which looked like a miniscule black grain, offers scientists remarkable insight into the first stage of evolution of a group that led to fish and eventually to humans.

"The bag-like body bears a prominent mouth and associated folds, and behind them up to four conical openings on either side of the body as well as possible sensory structures," researchers described the creature in a study published in the journal Nature.

"An anus may have been absent, and correspondingly the lateral openings probably served to expel water and waste material."

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