A reconstruction of how Wufengella would have looked like in life. Credit: Illustration made by Roberts Nicholls, Paleocreations.com
Key Points:
- A well-preserved fossilized worm dating from 518-million-years-ago resembles the ancestor of three major groups of living animals.
- Thanks to the fossils, the paleontologists have pieced together how brachiopods evolved to have two shells from ancestors with many shell-like plates arranged into a cone or tube.
- The researchers have linked the appearance of the fossil to the segmentation of the body of today’s earthworms.
An international team of scientists have discovered that a well-preserved fossilized worm dating from 518-million-years-ago resembles the ancestor of three major groups of living animals.
Measuring half-an-inch long, the worm, named Wufengella, was a stubby creature with a dense, overlapping array of plates on its back. Surrounding the asymmetrical armor was a fleshy body with a series of flattened lobes projecting from the sides. Bundles of bristles emerged from the body in between the lobes and the armor.
The researchers now show that the worm belonged to an extinct group of shelly organisms called tommotiids, which is tied to other groups.
Brachiopods are a phylum that resemble bivalves, such as clams, in having a pair of shells and living attached to the seafloor, rocks or reefs. Brachiopods filter water using a pair of tentacles folded up into a horseshoe-shape organ, called a lophophore. Brachiopods share the lophophore with two other major groups called the phoronids (horseshoe worms) and bryozoans (“moss animals”).
Molecular studies agree with anatomical evidence that brachiopods, bryozoans and phoronids are each other’s closest living relatives, a group called Lophophorata after their filter-feeding organ.
Thanks to the Wufengella fossils, the paleontologists have pieced together how brachiopods evolved to have two shells from ancestors with many shell-like plates arranged into a cone or tube. While the fossil fulfils the paleontological prediction that the lophophorates’ ancestral lineage was an agile, armored worm, the appearance of its soft anatomy brings into focus some hypotheses about how lophophorates may be related to segmented worms.
“Biologists had long noted how brachiopods have multiple, paired body cavities, unique kidney structures and bundles of bristles on their back as larvae. These similarities led them to notice how closely brachiopods resemble annelid worms,” said study author Jakob Vinther from the University of Bristol. “We now can see that those similarities are reflections of shared ancestry. The common ancestor of lophophorates and annelids had an anatomy most closely resembling the annelids. At some point, the tommotiid ancestor to the lophophorates became sessile and evolved suspension feeding. Then a long, wormy body with numerous, repeated body units became less useful and was reduced.”
Information provided by University of Bristol.