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Discovery of a 4-Centimeter Fossil Preserved in Carboniferous Rocks Allowed Scientists to Reconstruct for the First Time the Head of Arthropleura, a Terrestrial Arthropod That Lived Between 345 and 290 Million Years Ago and Could Reach Up to 3.2 Meters in Length and About 50 Kilos
A 4-centimeter fossil found in Montceau-les-Mines, France, allowed researchers to reconstruct for the first time the head of the giant Arthropleura, an arthropod that lived around 300 million years ago and could reach up to 3.2 meters in length.
The discovery was detailed in a study published on October 9, 2024, in the journal Science Advances. The work was led by researcher Mickaël Lhéritier and analyzed fossils from the Carboniferous period preserved within rocks.
The specimens analyzed were associated with the ancient fossil site of Montceau-les-Mines. Today the area is covered by an artificial lake, but in the past it was a tropical swamp environment located near the Equator.
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This small fossil ended up revealing a part of the body that remained unknown for over a century and a half. Despite the existence of several traces of Arthropleura, the front part of the animal had never been observed clearly.
The Fossil That Solved a Mystery of Over 150 Years
Since its discovery in 1854, Arthropleura was known mainly from body fragments and fossilized footprints. These records confirmed the existence of a giant terrestrial arthropod but did not reveal complete details about its anatomy.
The new analyzed fossil changed this scenario by preserving structures that remained hidden within the rock. To access this information, researchers used advanced imaging techniques that allowed them to examine the interior of the fossilized material.
Initially, the team used conventional tomography at a university facility. However, the images obtained did not have sufficient contrast to distinguish the delicate structures of the head region.
The analysis progressed when scientists turned to the European Synchrotron Radiation Facility, ESRF, located in Grenoble. At this stage, a multi-resolution approach was applied that allowed for observing the interior of the fossil nodule with greater precision.
According to researcher Vincent Fernandez, the sample was first scanned at low resolution. After that, the areas considered more promising were enlarged at higher resolutions.
Head Structures Appear for the First Time in the Fossil
The detailed examination of the fossil revealed anatomical characteristics never before described in the genus Arthropleura. For the first time, scientists were able to clearly observe mouthparts, antennae, and internal structures of the animal.
The three-dimensional digital reconstruction showed that the head had an approximately circular shape. It featured slender antennae and pedunculated eyes, in addition to a feeding apparatus made up of mandibles and two pairs of maxillae.
These structures had remained hidden within the rock since the animal’s fossilization. With the imaging analysis, Arthropleura was no longer known only by body segments and had its frontal part identified.
The researchers highlighted that the analyzed specimens were juvenile individuals. Nevertheless, they preserve a segmented organization that indicates growth through successive molts throughout life.
What the Fossil Revealed About the Lifestyle of Arthropleura
The new reconstruction also changed how Arthropleura is interpreted in relation to its behavior. Although it shows some features observed in carnivorous arthropods, the animal did not possess typical structures of active predators.
The researchers specifically pointed out the absence of venomous pincers. These structures are used by modern centipedes as hooks to capture prey.
The rest of the body reinforces this interpretation. Arthropleura had short legs and likely moved slowly, characteristics that do not indicate adaptation for fast chases.
The team concluded that the animal was probably detritivorous. This means it fed on decomposing plant material present in the soil of the Carboniferous forests.
In this environment, Arthropleura could act as a major biological recycler. Moving slowly through layers of organic debris, the arthropod would have played an important role in processing plant material.
How the Fossil Helps Understand the Evolution of Myriapods
In addition to anatomy, the study also analyzed the evolutionary position of Arthropleura among the myriapods. To do this, scientists combined morphological data with phylogenetic analyses based on transcriptomic information.
The results indicate that Arthropleura occupies a position close to the stem group of millipedes. At the same time, it preserves characteristics that also resemble centipedes.
This combination of features helps explain why the classification of the animal remained uncertain for so long. Without the presence of the head, each new fossil contributed fragmented information but did not solve the puzzle.
With the new reconstruction, it became possible to observe structures that connect different lineages of myriapods. Arthropleura exhibits traits shared by both millipedes and centipedes.
The Scientific Value of the 305-Million-Year-Old Fossil
The study concludes that the analyzed fossil is approximately 305 million years old. This age makes it an important record for understanding the diversity of terrestrial arthropods during the Carboniferous period.
The reconstructed head offers an anatomical link between groups that are often compared only based on molecular data from current species. The fossil preserves a combination of features that do not appear in exactly the same way in any living animal.
The researchers intend to continue examining the material collected in Montceau-les-Mines. Before the site was covered by the artificial lake, more than 100,000 fossils were recovered from the region.
These specimens may still reveal additional details about the arthropods that inhabited the tropical forests of the Carboniferous. For the genus Arthropleura, at least, the newly analyzed fossil finally fills a historical gap in the understanding of its anatomy.
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