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Scientists unveil the head of a prehistoric giant arthropod
18-10-2024
Arthropleura, one of the largest arthropods that ever existed (length up to 2.6 meters), finally 'has' a head. A team from the Université Claude Bernard Lyon 1 and the ESRF has scanned a whole fossil specimen of the Carboniferous period. The results show that the head bears surprising traits typical of centipedes, whilst its body has a millipede structure.
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Arthropleura lived between 345 million and 290 million years ago, in what is now North America and Europe. First discovered in 1854, paleontologists’ knowledge on Arthropleura was mostly based fragmentary fossils and also fossilized trackways. Until today, they did not know what the head of Arthropleura looked like.
Now an international team of scientists led by the Université Claude Bernard Lyon 1 (France) and the ESRF, have discovered that the head of Arthropleura has traits typical of centipedes, whilst its body has a millipede structure, with two pairs of legs per segment. The specimen scanned by the team is a 305 million years old fossil recovered from the site of Montceau-les-Mines, which is today covered by an artificial lake. During the Carboniferous, this area was situated near the equator, with a tropical, swampy environment. The studied fossil was tiny compared to the largest version of the creature, as it was a 4cm long juvenile, but the whole body was intact, embedded in the sediment.
Originally, the team used conventional computed tomography at the university lab, but soon found that there was not enough contrast to recover all the details of the head. Then they turned to Vincent Fernandez at the ESRF: “On BM18 we first scanned the nodule in low resolution, then we selected the parts that were most interesting and zoomed onto them in a multiresolution approach”, explains Fernandez.
Mickaël Lheritier, first author of the paper, explains the importance of the ESRF in the research: "The ESRF was crucial in our investigation because it enabled us to observe with a better quality the feeding apparatus and the antennae, as well as revealing the mandibles that were hidden inside the head of the animal".
The scientists found that Arthropleura's head was roughly circular, with slender antennae, stalked eyes, and underneath a pair of mandibles and two pairs of additional feeding appendages called maxillae. Despite some features of its feeding apparatus resembling the carnivorous centipedes, Arthropleura lacked some predatory traits, like venomous forcipules (modified first set of centipede legs) or specialised limbs for catching prey. Its body structure, such as its short legs and slow-moving gait, suggests it was not a fast predator but more likely a slow-moving detritivore, so scientists conclude that it probably fed on decaying vegetal matter.
The next step for the team is to dig into the more than 100 000 fossils that were collected from the Montceau-les-Mines site before it was filled with water and to try to find other Carboniferous arthropods that can contribute to provide a clearer picture of how fauna was at the time.
Reference:
Lheritier, M., et al, Science Advances, 9 Oct 2024, Vol 10, Issue 41 DOI: 10.1126/sciadv.adp6362
Text by Montserrat Capellas Espuny