The largest arthropod ever was a car-sized millipede-like creature — and now it has a face
New fossils reveal the head of the largest arthropod ever to live.
by Tibi Puiu · ZME ScienceFor more than a hundred years, scientists have been chasing the face of a creature so large and bizarre it feels almost mythical. Arthropleura, a colossal millipede-like beast that scuttled through the lush forests of ancient Earth, has been an enigma ever since its discovery. Fossils of its massive, segmented body have hinted at a creature of terrifying proportions, but one crucial piece was missing: its head.
Now, after decades of searching, paleontologists have finally uncovered the face of this Paleozoic titan. Two newly unearthed fossils, preserved with extraordinary detail, have given scientists their first glimpse of Arthropleura’s head. What they found is both remarkable and strange, offering new insights into a creature that once grew to over eight feet long. That’s longer than a king-sized bed or about the size of a car — and ruled Earth’s swamps some 300 million years ago.
“Arthropleura . . . has been known since the 18th century, over 100 years, and we hadn’t found a complete head,” Mickaël Lhéritier, a paleontologist at Claude Bernard Lyon 1 University in France and lead author of the new study, told Live Science. “Now with the completed head, you can see the mandibles, the eyes, and these characteristics can [help us understand] the position of this [creature] in evolution.”
A Monster of the Carboniferous
Imagine walking through the dense, tropical forests of the Carboniferous period, around 300 million years ago. Towering plants and colossal trees dominate the landscape, and underfoot, among the roots and decaying leaves, crawls a giant. Arthropleura was an invertebrate unlike anything alive today. It stretched over eight feet in length, weighed over 100 pounds, and its body was divided into armored segments that slithered and undulated as it moved.
When the first fossilized segments of Arthropleura were discovered in the mid-1800s, paleontologists were stunned by its sheer size. For years, they puzzled over how such a large arthropod could have existed. But without the head, many questions remained unanswered.
Scientists knew that it had a millipede-like body, with two pairs of legs per segment, but Arthropleura’s exact place in the arthropod family tree remained uncertain. Was it closer to the centipedes, with their flattened bodies and venomous jaws, or the millipedes, which are gentle decomposers?
Now, thanks to micro-CT scans of the two newly discovered juvenile fossils, the answer may be closer at hand.
“We discovered that it had the body of a millipede, but the head of a centipede,” explained Lhéritier in an interview with AP. The fossils, pulled from ancient rock in Montceau-les-Mines, France, revealed Arthropleura’s antennae, mandibles, and — perhaps most surprisingly — stalked eyes, the kind typically seen in creatures that spend time in water.
This peculiar combination of features suggests that Arthropleura may have lived a life more complex than scientists previously imagined.
A Creature of Land and Water?
The discovery of Arthropleura’s head, complete with its stalked eyes, opens a new window into its peculiar life. Scientists have long assumed that this giant invertebrate roamed the land. However, its eye structure raises the tantalizing possibility that Arthropleura might have spent part of its life underwater, at least as a juvenile.
“The stalked eyes remain a big mystery, because we don’t really know how to explain this,” Lhéritier admitted. Stalked eyes are a feature commonly seen in aquatic arthropods like crabs, suggesting that Arthropleura’s young may have been semi-aquatic, lurking in ancient swamps before making their way onto land as adults.
This finding adds a new twist to the mystery of how such creatures became so large. Some scientists have suggested that the high oxygen levels of the Carboniferous period allowed invertebrates to grow to sizes far beyond what we see today. But Arthropleura fossils predate the peak of this oxygen surge, indicating that something else — perhaps the warm, humid climate and dense forests — fueled their massive growth.
What did Arthropleura eat? Did both males and females grow to these monstrous sizes? And how long did it take these creatures to reach their full size? These are questions still waiting for answers.
Despite its immense size, Arthropleura vanished from the Earth around 298 million years ago, during the Permian period. The reasons for its extinction are unclear, but scientists speculate that a drying climate or competition from early reptiles may have sealed its fate.
The findings appeared in the journal Science Advances.