300-Million-Year-Old Fossils Reveal What Worlds Biggest Arthropod Looked Like

The giant arthropod ‘Arthropleura', which roamed the Earth over 300 million years ago, combined traits of millipedes and centipedes, new fossils have revealed. These fossils, from juvenile specimens, were found in France and have finally solved a nearly 200-year-old mystery about the creature's head structure. It also offers fresh insights into its lifestyle and evolutionary relationships.

Arthropods, a diverse group of invertebrates, are known for their segmented bodies, jointed legs and exoskeletons. This group includes insects, crustaceans, and arachnids, but Arthropleura holds a particularly important place in history as the largest arthropod ever to live on Earth.

First discovered in Great Britain in 1854, fossils of Arthropleura showed that adults could reach a massive 8.5 feet in length. However, until now, no fossils with preserved heads were found, making it difficult to determine whether Arthropleura was a predator like centipedes or a detritivore like modern millipedes.

This recent discovery, detailed in the journal Science Advances on October 9, is considered a breakthrough. Using advanced scanning techniques such as micro-computed tomography and synchrotron imagery, researchers analysed the fossils encased in stone without damaging them. The scans revealed intricate details, including antennae, mandibles, eyes and feeding structures. 

According to Dr Greg Edgecombe, a palaeontologist at London's Natural History Museum, “Millipedes and centipedes are actually each other's closest relative,” a point illustrated by the features found in the Arthropleura fossils.

The findings suggest that Arthropleura likely wasn't a predator. With no venom fangs or specialised predatory legs, the creature probably lived a lifestyle similar to modern detritus-eating millipedes. “They were probably more like the detritus-eating millipedes alive today,” Mr Edgecombe added.

The creature's stalked eyes – more commonly seen in aquatic arthropods like crabs – raise the possibility that it may have lived a partially amphibious life. “Today, stalked eyes are a typical feature of aquatic arthropods like crabs or shrimps,” explained Mickael Lheritier, lead author of the study. Future discoveries, particularly of its respiratory system, could further shed light on Arthropleura's connection to water, he said.

James C. Lamsdell, a geology professor at West Virginia University, praised the discovery, noting that these “remarkable findings” offer a new understanding of this long-extinct giant.