The team believes the palaeoscolecid lived on ocean floors.

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Today, paleontologists, scientists, and researchers near and far still gather data on the most ancient creatures to ever cross the Earth, and this is largely thanks to the "Cambrian explosion." This event took place between 530 and 540 million years ago; its impact revealed the first signs of animals in fossil records. The findings from this time period help us study the evolution of the creatures alive today. As for one of the most recent animal discoveries? In a study published in Acta Palaeontologica Polonica, researchers out of the University of Missouri found an ancient worm-like fossil with the same anatomical makeup as modern worms—however, it isn't something that would be found on Earth in the present day.

"This group of animals are extinct, so we don't see them, or any modern relatives, on the planet today," Jim Schiffbauer, an associate professor of geological sciences in the University of Missouri College of Arts and Science and one of the study's co-authors, said. "We tend to call them 'worm-like' because it's hard to say that they perfectly fit with annelids, priapulids, or any other types of organism that we would generally call a 'worm.' But palaeoscolecids have the same general body plan, which in the history of life has been an incredibly successful body plan. So, this is a pretty cool addition, because it expands the number of worm-like things that we know about from 500 million years ago in North America and adds to our global occurrences and diversity of the palaeoscolecids."

paleontologists digging for fossils in wester utah
Credit: PATRICK T. FALLON/AFP via Getty Images

Wade Leibach, a University of Missouri graduate teaching assistant in the College of Arts and Science and lead author on the study, thinks that this palaeoscolecid spent its lifespan slithering on ocean floors. "It is the first known palaeoscolecid discovery in a certain rock formation—the Marjum Formation of western Utah—and that's important because this represents one of only a few palaeoscolecid taxa in North America," he said. "Other examples of this type of fossil have been previously found in much higher abundance on other continents, such as Asia, so we believe this find can help us better understand how we view prehistoric environments and ecologies, such as why different types of organisms are underrepresented or overrepresented in the fossil record."

To reach these conclusions, Leibach centered his research around the indentations in the fossil near the palaeoscolecids' microscopic plates: "These very small mineralized plates are usually nanometers-to-micrometers in size, so we needed the assistance of the equipment in Dr. Schiffbauer's lab [at the University of Missouri X-Ray Microanalysis Core] to be able to study them in detail. Their size, orientation, and distribution is how we classify the organism to the genus and species levels." As for why this critter type went extinct? It was likely ecological competition, explained Leibach, that didn't allow these organisms to survive in some areas.

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