Saccorhytus: This Ugly Bag-like Creature Is Our Oldest Known Ancestor

This pre-historic creature did not have an anus. It would eat and excrete from the same orifice. And it does not have much in common with modern humans. But scientists say that the newly discovered creature Saccorhytus coronaries is our oldest known ancestor. Fossils of this ugly, bag-like sea organism were unearthed from Xi’An, Shaanxi Province in central China.

The organism lived 540 million years ago

Findings of the study were published in the journal Nature. The creature, measuring just a millimeter in size, lived between the grains of sand on the seabed about 540 million years ago. Paleontologists said the fossils were “exquisitely well preserved.” Saccorhytus is the oldest example of a category of animals knows as deuterostomes that are common ancestors of a variety of species, including humans.

The study was conducted by an international team of paleontologists from the UK, China, and Germany. Prof Simon Conway Morris of the University of Cambridge told BBC News that the organism looks like tiny black grains to the naked eye. But the level of details under the microscope was “jaw-dropping.” Researchers had to process through three tons of limestone to get to the fossils.

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Saccorhytus had a bilaterally symmetrical body

There are a few deuterostome groups known from 510 million to 520 million years ago. But these groups had already started diversifying into vertebrates, echinoderms, hemichordates, and sea squirts. Their diversity made it difficult for researchers to figure out what the common deuterostome ancestor looked like. The discovery of Saccorhytus offers a look at the common ancestor of all deuterostomes.

Scientists found that the Saccorhytus had a bilaterally symmetrical body. The characteristic was passed down to many of its descendants, including humans, through millions of years of evolution. The creature had a thin and flexible skin, which led researchers to believe that it moved around by contracting its muscles. It could wriggle around in the ocean water to find food.

Comparing Saccorhytus’ genetic structure with other species

What surprised scientists was its large mouth relative to its body. Tiny conical structures around the mouth might have allowed the swallowed water to escape. Scientists believe these structures could have been the precursor to gill stilts.

Now that it has been established that deuterostomes existed about 540 million years ago, scientists can use the “molecular clock” to determine when the explosion in animal diversity occurred. Researchers can figure out when two groups began to diverge by quantifying the genetic differences between them. However, there are only a few fossils of Saccorhytus coronaries, which makes it difficult to compare its genetic structure with other species.