The largest land arthropod ever was a millipede longer than a person
Around 300 million years ago, a millipede called Arthropleura crawled through open woodland in Europe and North America, reaching at least 2 metres long and leaving trackways half a metre wide. For over 170 years scientists argued about what it was, and only in 2024 did anyone clearly see its head.
It lived from roughly 344 to 292 million years ago, spanning the early Carboniferous into the early Permian, in sparsely wooded ground near water, and it may have been partly amphibious. Its name, from Greek words for joint and rib, refers to the way its armour splits into a central band and side plates. A shed skin reported in 2021 suggests an animal perhaps 1.9 to 2.63 metres long and about 50 kilograms, rivalling the giant sea scorpion Jaekelopterus. Adults carried 28 to 32 body segments, each with two pairs of legs, while juveniles had fewer, adding segments as they moulted.
The first fossils turned up in 1849 during railway construction near Friedrichsthal in Germany, and early experts filed them under crustaceans. Hermann von Meyer linked the remains to decapods, others compared them with trilobites or isopods, and only in 1911 did Lewis Moysey and Henry Woodward connect Arthropleura with the myriapods. Gerard Waterlot's influential 1934 study placed it beside trilobites and imagined two-branched legs with gills, a carnivorous diet and a life on lake beds, though Leif Stormer later showed the legs had a single branch. The best adult fossil, a 90 centimetre specimen described in 1935, was carefully cut from the roof of a German coal mine.
The head stayed a mystery into the 21st century; at one stage researchers even decided the supposed head was really the first segment behind it. The answer came from two nearly complete juveniles from Montceau-les-Mines in France, scanned with micro-CT in 2024. The original head identification was right after all. What Waterlot had taken for feeding limbs were paired plates guarding the head like a car bumper, beneath which sat two pairs of maxillae and internal mandibles resembling a centipede's. It also had antennae and, unlike any living myriapod, stalked compound eyes.
That study placed Arthropleura just outside the living millipede group, as its closest relative, partly because it bore a pair of legs under the first segment behind the head, which modern millipedes lack. How it breathed is still debated: some researchers see hollow plates at the leg bases as respiratory sacs, others as simple reinforcement for walking.
Source: Arthropleura
