Head of 340-million-year-old car-sized bug revealed after centuries of mystery

The face of Arthropleura , a car-sized, millipede-like creature and the largest arthropod to ever exist, has finally been unveiled, thanks to the discovery of two well-preserved fossils.

According to new research, the head of Arthropleura consisted of a round, bulbous structure with two short, bell-shaped antennae. It also had two protruding eyes, similar to those seen on crabs today, and a relatively small mouth designed for grinding leaves and bark—suggesting that this giant arthropod was a plant-eater.

Despite its fearsome size, the creature’s diet likely consisted of vegetation, including leaves and bits of bark from the lush forests it inhabited.

This colossal arthropod roamed the Earth between 346 and 290 million years ago, during the late Paleozoic era. Living in forests near the equator, Arthropleura thrived in an oxygen-rich atmosphere that enabled it to grow up to an astonishing 8.5 feet (2.6 meters) in length and weigh over 100 pounds (45 kilograms).

Body of a millipede, head of a centipede

Although fossils of this ancient giant had been discovered before, scientists were previously unable to determine what its head looked like. Many of the Arthropleura fossils found over the years were missing their heads, leaving only the body’s segmented shell.

These headless remains are believed to be molted exoskeletons left behind as the creature grew. Like other arthropods, Arthropleura would shed its exoskeleton through the head opening, leaving behind clues of its massive size but no indication of its facial structure.

The lack of head fossils left scientists speculating about what the top end of this massive bug might have looked like. However, recent discoveries of juvenile Arthropleura fossils, which were far more complete than those found before, have finally given researchers a long-awaited opportunity to study its head.

Arthropleura was an arthropod, a group that includes modern-day insects, crabs, and spiders, and it shared characteristics with present-day centipedes and millipedes. However, it was much larger and had a unique blend of features.

“We discovered that it had the body of a millipede, but the head of a centipede,” explained study co-author Mickael Lheritier, a paleobiologist at the University Claude Bernard Lyon in Villeurbanne, France. This combination of features made Arthropleura an unusual and formidable creature in its time.

Examining juvenile fossils

For a long time, paleobiologists have been eager to understand what the head of this giant arthropod looked like. “We’ve been wanting to see what the head of this animal looked like for a really long time,” said James Lamsdell, a paleobiologist at West Virginia University who was not involved in the study.

To model the head, researchers used advanced CT scanning techniques to examine fossil specimens of juvenile Arthropleura . These fossils , found in a French coal field in the 1980s, were still embedded in rock. The CT scans allowed the team to examine hidden details without damaging the fossils.

“When you chip away at rock, you don’t know what part of a delicate fossil may have been lost or damaged,” Lamsdell explained, emphasizing the value of non-invasive techniques.

Though the juvenile fossils measured only around 2 inches (6 centimeters) long—far smaller than the giant adults—the researchers believe they provide crucial insights into the appearance of Arthropleura .

These smaller specimens may not have grown to the same enormous size as their adult counterparts, but they still offer valuable clues about what this prehistoric titan looked like during its reign over 300 million years ago.

The study has been published in Science Advances .