An armored ‘worm’ that spread across ocean reefs 518 million years ago is the ancestor of three groups of aquatic animals that live very different lifestyles today and offers new clues about the explosion of various species in that moment, according to a new study.
An international team of researchers recently discovered the fossil of a species that gave rise to brachiopods, bryozoans and phoronids; these three groups of filter-feeding sea creatures fixate on the seafloor, but each group has highly specialized feeding structures and looks very different from one another.
The fossil species, named Wufengella bengtsoni, is a member of an older, shelled group of organisms called tommotiids, scientists reported in a new study.
The find adds a new piece to the puzzle of how animals evolved during the Cambrian explosion, a time during the Cambrian period (541 million to 485.4 million years ago) when early life rapidly diversified into the Earth, introducing and establishing a variety of different body plans. which we still see today in living animals.
Brachiopods are bivalve creatures with a shell; bryozoans have soft bodies with crowns of tentacles, and phoronids are enclosed in protective tubes made of chitin, a material that strengthens organic structures such as exoskeletons, beaks, and shells.
The fossil of Wufengella and a drawing describing the main components of the organism. (Jakob Vinther and Luke Parry)
Before the discovery of W. bengtsoni, taxonomists had speculated that the ancestor of all these groups of animals might have been a segmented worm-like tommotiid, based on similarities in the embryonic development of the groups in living animals.
But while researchers had some idea of what this hypothetical ancestor might look like, they weren’t sure if they would ever find it.
“One of the things we often mentioned when we were sitting in the pub fantasizing about what we might hope to find one day was this elusive tommotiid,” co-author Jakob Vinther, associate professor of macroevolution at the University of Bristol. in England, he told Live Science.
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The fossil was found at the Chengjiang Biota fossil site in Yunnan, a province in southwestern China. It’s a rare find because animals like this aren’t usually preserved well enough for paleontologists to study them in detail.
“They were spreading around the reefs in the shallow tropical waters that existed then,” Vinther said.
In these ancient reef systems, dead animals were typically washed up until their bodies disintegrated, and their soft tissues often decayed in the oxygen-rich reef waters before fossilization could occur.
“This particular animal, luckily for us, was washed into deep water where it was buried in the mud where it was preserved,” Vinther said.
While the researchers predicted the general body plan of W. bengtsoni, some features of the fossil came as a big surprise. It had flaps on its body that could have been used for suction, to secure the animal to the reef when there were waves, Vinther speculated.
The species also had long bristles on its sides that may have been used to detect prey or as protection against predators.
The study authors aren’t sure what the animal was eating, but its body wasn’t adapted to filter water or stand still, so they know it wasn’t a bottom-bound filter feeder marine like their descendants.
Researchers believe it is the ancestor of brachiopods, bryozoans and phoronids because it shared a similar skeleton with those groups. As life evolved in the Cambrian explosion, animals filled different ecological niches and adopted different body plans.
“Sometimes ancestors can look very, very different from their closest living relatives,” Vinther said.
Martin Smith, an associate professor of paleontology at Durham University in England who was not involved in the study, described the new research as an example of “flawlessly executed” science. “It’s a fantastic study,” Smith said.
“We’re really seeing how these groups fit together and how they evolved from a single common ancestor. It’s taking us up a rung on the evolutionary tree,” Smith added.
“It’s the next frontier, we’re going to go a little deeper in time and we’re really starting to see the origin of the Cambrian explosion when all the complex body plans appear.”
The study was published online Sept. 27 in the journal Current Biology.
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This article was originally published by Live Science. Read the original article here.