New species of ‘Dune-like’ carnivorous worm described from UK fossils
By Emma Caton
A new species of ancient worm which could have been plucked straight from the pages of a sci-fi novel has recently been described by scientists.
The carnivorous worms are thought to have dragged themselves along the sea floor, consuming whatever prey they could find during the early explosion of life on our planet.
Carnivorous worms may sound like something straight out of the popular blockbuster Dune, but this newly described species was found much closer to home.
Fossils of the new species, now called Radnorscolex latus,were found in an old quarry in Herefordshire and date to around 425 million years ago when the area would have been deep underwater at the edge of a continental shelf.
R. latus was a burrowing predator that belonged to an extinct group of worms called Palaeoscolecida. Although it only grew up to 10 centimetres long, it had a truly terrifying way of engulfing unsuspected prey that wandered too close on the seafloor during the Silurian Period.
Dr Richie Howard, Curator of Fossil Arthropods at the Natural History Museum who helped name and describe the species, says, “They had a retractable throat which was covered in rows of sharp teeth that they would throw out to catch prey.”
“We think they weren’t too picky when it came to feeding and likely just shoved their throat out into the mud and just grab anything they could find. They certainly make you think of the sandworm in Dune or the Xenomorphs from Alien!”
Although the fossils were found in the 1920s, they were relatively understudied at the time and have remained a part of the Natural History Museum’s collections since then. The remains were originally assigned to a genus called Protoscolex, which acted as a “wastebasket taxon” where fossils end up when their classification is uncertain.
In other groups with less simple worm-like bodies it may be features of the head or appendages preserved in the fossil record that are used to help classify a species.
But most fossils of palaeoscolecids are usually very incomplete with impressions of the skin being all that remain. They were covered in tiny armour plates and the shape and distribution of these help to differentiate the different species.
It is therefore the texture of this skin that is most commonly used to determine their taxonomy.
“In the 1920s, trying to analyse the skin of these tiny animals was difficult, which is why a lot of these species were understudied or undescribed completely,” says Richie.
“Today, our scientists can use more advanced, state-of-the-art technology, like scanning electron microscopes to help make a more thorough description of the species. We eventually assigned the worm to the genus Radnorscolex due to its similarity to other fossils that were found in Wales, which lived around 40 million years earlier.”
They were also able to examine the way in which these ancient worms may have moved along the muddy sea floor.
“On their heads they had rows of backwards facing spines,” explains Richie. “The worms might have used these as an anchor to dig into the ground and then drag its body with the help of rings of muscles that would have moved in an out like an accordion to propel it forward.”
Scientists believe the palaeoscolecids might have been early relatives of penis worms or arthropods, a group which includes animals like centipedes, spiders and the horseshoe crab.
The palaeoscolecids first appeared around 520 million years ago during the Cambrian explosion, a time which saw the rapid expansion of life on Earth and when most major animal groups started to appear in the fossil record.
Palaeoscolecids were a successful group of animals for around for 100 million years, spanning three geological time periods: the Cambrian, Ordovician and the Silurian. They were particularly diverse and widespread during the Cambrian and Ordovician and their remains from this time have been found all over the world.
But younger members of the palaeoscolecids that lived during the Silurian Period have rarely been studied and their remains aren’t well documented in the fossil record. This is probably because at the end of the Ordovician, the Earth experienced its first mass extinction when a rapid drop in temperature formed huge glaciers and resulted in a drop in sea levels. As a result, around 86% of all species were went extinct.
As the remains of R. latus date to the Late Silurian, scientists believe they might have been some of the last surviving species of palaeoscolecids, as the group are thought to have gone extinct soon afterwards about 424 million years ago.
This means that the new species could be described as a living fossil of the Silurian, similar to how we view horseshoe crabs or coelacanths today.
“Following the Ordovician mass extinction, it seems like palaeoscolecids may have been impacted and that’s why we don’t see as many of them in the Silurian,” says Richie.
“We think they could have been a low diversity group that hung on after the mass extinction before eventually becoming extinct not long after this specimen of R. latus would have lived.”
“But it could also be because they are a very understudied group. We are the only ones that have properly described the younger palaeoscolecids from the third time period of their existence. So, we are laying the groundwork for further study in the future.”
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