400-million-years old giant worm discovered

Websteroprion armstrongi fossil (Photo courtesy Luke Parry)
Websteroprion armstrongi fossil (Photo courtesy Luke Parry)

An article published in the journal “Scientific Reports” describes the discovery of a primitive worm with jaws that are huge compared to its body’s size. Called Websteroprion armstrongi, it was studied by a team of researchers after a fossil specimen was discovered at the Royal Ontario Museum, where it was stored in the mid ’80s. It seems to belong to the class of polychaetes (Polychaeta), a marine relative of earthworms and leeches that lived about 400 million years ago.

It’s not the first time that paleontologists discovered polychaete fossils dating back to the Paleozoic era, in fact they were found until the beginning of the Cambrian period, about 540 million years ago. However, most of the data on this group derives from microfossils of jaws that have a size ranging from 0.1 to 2 mm which are well preserved. The fossil subject of this new research however has jaws that could reach a length of one centimeter. The comparison with living species suggests that its body could exceed one meter in length.

In essence, Websteroprion armstrongi was a giant worm so it can also be studied with the naked eye where the microfossils of its smaller relatives always require studies under the microscope. Today there are giant marine polychaetes as well, in particular Eunice aphroditois, the so-called “Bobbit worm”, a predator that uses its jaws to attack prey such as fish and cephalopods.

However, it’s the first time that gigantism among polychaetes is discovered in the Paleozoic era. From the study carried out by researchers led by Professor Mats Eriksson of Lund University they deduced that this phenomenon is restricted to a certain group of polychaetes and within that group it evolved many times in different species in the course of the geological eras.

The specimens studied were discovered in June 1994 by Derek K Armstrong of the Ontario Geological Survey during a survey on rocks and fossils of a remote area in Ontario. Various rock samples belonging to the Kwataboahegan Formation dating from the Devonian period were taken to the Royal Ontario Museum, where they remained in stock until they raised the curiosity of this research’s authors.

David Rudkin of the Royal Ontario Museum, one of the authors of the research, noted the importance of examining museum collections to make important discoveries in neglected samples. In the field of paleontology occasionally such cases happen, also thanks to modern technology applied to this field which allow more in-depth and non-destructive exams.

In the case of worms, a problem is the fact that their soft parts don’t fossilize well so typically only small parts of their bodies are found and in particular their jaws. Those of Websteroprion armstrongi are particularly large but are still just one centimeter long. Luckily they were eventually identified and studied.

Reconstruction of Websteroprion armstrongi attacking a fish (Image courtesy James Ormiston)
Reconstruction of Websteroprion armstrongi attacking a fish (Image courtesy James Ormiston)

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