A well-preserved fossilised worm from over 518 million years could be the ancestor of three major groups of living animals, according to an international team including researchers from the University of Bristol, University of Oxford and the Natural History Museum.
According to the University of Bristol, the creature is called Wufengella bengtsoni, and the 1.2 centimetre-long fossil was unearthed in China and belongs to a small creature with a layer of dense overlapping array of plates on its back. It belongs to an extinct group of shelly organisms called tommotiids. The asymmetrical armour surrounds a fleshy body with flattened lobes jutting out from the side.
The space on its body between the armour and the lobes houses bundles of bristles. According to the researchers, the lobes, bundles of bristles and the array of shells on the back are evidence that the worm was originally segmented like an earthworm. The research has been published in an article in the journal Current Biology.
Animals are separated into more than 30 categorie known as phyla. Members of each phylum have a set of features that set them apart from others. Only a few features are shared among members from different phyla, and this can be attributed to the fast rate of evolution during the period when these major groups originated. This period is known as the Cambrian explosion and happened approximately 550 million years ago.
“Wufengella belongs to a group of Cambrian fossils that’s crucial for understanding how lophophorates evolved. They’re called tommotiids, and thanks to these fossils we have been able to understand how brachiopods evolved to have two shells from ancestors with many shell-like plates arranged into a cone or tube,” said co-author Luke Parry from the University of Oxford, in a press statement.
A Lophophore is a horseshoe-shaped organ that consists of folded-up tentacles used to filter water. This organ is shared by members of three major phyla, including Brachiopods, Phoroids and brozoans Molecular studies and anatomical evidence suggests that brachipods, bryozoans and phoronids are each others’ closest living relatives. The three phyla can be grouped into a clade called Lophophorata, named after the filter-feeding organs.
“We have known for a long time about this tommotiid group called camenellans. Palaeontologists have thought that those shells were attached to an agile organism—crawling around—rather than being fixed in one place and feeding with a lophophore,” added Parry. The research team demonstrates that Wufengella is a camenellan tomootiid, meaning that it is the long sought-after wormy ancestor to the lophophorates.
The fossil proves the prediction that the lophophorates share an ancestor that was an agile, armoured worm but its soft anatomy also suggests hypotheses about how lophophorates may be related to segmented worms
“We get an incomplete picture by only looking at living animals, with the relatively few anatomical characters that are shared between different phyla. With fossils like Wufengella, we can trace each lineage back to its roots, realising how they once looked altogether different and had very different modes of life, sometimes unique and sometimes shared with more distant relatives,” added co-author Greg Edgecombe from the Natural History Museum, in the press statement.