Spiny trunks, short legs and “little wings”: paleontologists present other representatives of the strange creatures that roamed the seas about half a billion years ago. As they explain, the two new specimens are two interesting pieces of the puzzle when researching the evolutionary history of arthropods. How exactly the freaks, about 462 million years old, fit into the picture is still questionable. Scientists now hope to find more discoveries at the promising new site in Wales that may shed more light on the early evolutionary history of arthropods.
In quantitative terms, they are the most successful of all animal groups: about 80 percent of animal species living today belong to arthropods, such as insects, crabs, and spiders. The evolutionary origin of this group is believed to lie in the so-called Cambrian explosion of life over 520 million years ago. Many fossils already indicate early stages of development. But the relationship between different fossil organisms still baffles researchers. Because despite some of the characteristics of arthropods, they were sometimes very strange creatures, which are sometimes referred to as “strange wonders”. Particularly famous is the bizarre predator Anomalocaris with its radial mouthparts and spiny appendages, as well as the fuzzy five-eyed creature Opabinia.
Now the pool of primal freaks is growing: the finds come from a newly discovered fossil deposit in which traces of organisms survived from the Ordovician-time some 40 million years after the Cambrian explosion. The site is a quarry in central Wales surrounded by sheep pastures. At first only fossil sponges were discovered there. But then co-author Joseph Botting, of the National Museum of Wales in Cardiff, discovered something special: “I discovered something that at first glance looked like a creature with a tentacle sticking out of a tube,” says Botting. He showed it to his colleague Lucy Muir and was excited: “It was clearly a real soft-bodied preservation – something paleontologists dream about. We didn’t sleep well that night because of the excitement,” says the scientist.
Strange little creatures on the horizon
Indeed, the discovery developed into a comprehensive investigation in collaboration with international colleagues. Another specimen was discovered at the site. As the researchers report, these are very cute little representatives of the “strange wonders of the world.” More detailed investigations using modern methods of analysis revealed that the largest specimen was 13 millimeters in size, while the smaller specimen was only three millimeters in length. However, microscopic investigations have provided insights into the partially well-preserved structures of organisms that are about 462 million years old.
Some features are similar to those of Opabinia, such as the triangular stem legs, which may have been used to interact with sediments. The tail fan was also visible in the smaller specimen, as observed in Opabinia’s recently described sister group, Utaurora. The newly discovered organisms also have the literally standout feature that Opabinia also possesses: a trunk. But in this case it was covered in spikes and the animals also had unusual hard structures on their heads. The authors explain that these features were not previously known from any opabiniids, and thus suggest a possible relationship with radiodonts including anomalocaris.
As they continue to report, it is not yet clear whether the two specimens are two species or just one species. Because the smallest specimen could be a young animal. “The size of the smallest is comparable to that of some modern arthropod larvae – we had to take this possibility into account in our analyses,” says senior author Joanna Wolfe from Harvard University, Cambridge (USA). So the researchers used only the larger sample as a basis for describing the new species. They called it Mieridduryn bonniae. The genus name Mieridduryn comes from Welsh and translated means blackberry nose – referring to the animal’s thorny trunk.
Notes on the evolution of arthropods
The paleontologists then conducted phylogenetic analyses, comparing the new fossils to 57 living and fossil arthropods to examine their place in evolutionary history. “The best supported position for our Welsh specimens, whether considered as one or two species, was more closely related to modern arthropods than to opabiniids. These analyzes indicate that Mieridduryn and the smaller specimen are not true opabiniids,” says lead author Stephen Pates from the University of Cambridge (UK). ).
As the researchers point out, this explanation in turn leads to an interesting relationship to the evolutionary history of arthropods. This may mean that the proboscis—which is thought to represent a fused pair of head appendages—was not unique to opapinids. It may also be present in the common ancestor of xrays and early modern arthropod ancestors. Scientists say the microscope may have evolved back into the so-called labrum that covers the mouth of modern arthropods.
But as they stress, the classification remains unclear. Because it also seems possible that Mieridduryn could have been representative of the Opabiniids. It is possible that their features, such as spines and shields, were only the result of a parallel evolution that made them look similar to Diodontes. But until then, the finds will be significant, the scientists point out: They will then be the smallest known opabiniids and the only ones ever discovered outside of North America. Whatever the outcome, fossils are an important new piece of the puzzle in the evolutionary history of arthropods, say the researchers. That is why they are now continuing their quarry work in the sheep pasture and hoping for more discoveries. “Even the sheep seem to have noticed we’re up to something special here,” Muir concludes.
Source: Harvard University, professional article: Nature Communications, doi: 10.1038/s41467-022-34204-w
“Alcohol buff. Troublemaker. Introvert. Student. Social media lover. Web ninja. Bacon fan. Reader.”