The study says that the fossils reveal the head of the largest known arthropod in the world

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For nearly two centuries, scientists have tried to solve an enduring mystery involving a giant millipede-like animal called Arthropleura, which used its multiple legs to roam the Earth more than 300 million years ago.

Now, two well-preserved fossils of the creature discovered in France have finally revealed what the arthropod’s head looked like, providing insight into how giant arthropods lived.

Today, arthropods are a group that includes insects, crustaceans, and arachnids such as spiders and their relatives – and the extinct arthropods remain the largest arthropods ever known to inhabit the planet.

Scientists in Great Britain first discovered arthropod fossils in 1854, with some adult specimens reaching 8.5 feet (2.6 meters) in length. But none of the fossils included a head, which will help researchers determine basic details about the creature, such as whether it was a centipede-like predator or an animal that fed only on decaying organic matter like millipedes.

In an attempt to find the first complete head, researchers conducted an analysis of arthropod fossils belonging to two juvenile individuals that were discovered in the 1970s in France. The results were published on October 9 in the journal Advancement of science.

The strange story of Arthropleura gained a new twist when the study team surveyed fossils still trapped in stone.

The head of each animal shows characteristics belonging to both millipedes and centipedes, suggesting that the two arthropod species are more closely related than previously thought, according to the study’s authors.

“By combining the best available data from hundreds of genes from the living species in this study, along with physical characteristics that allow us to place fossils like Arthropleura on evolutionary trees, we were able to square this circle,” said study co-author and paleontologist Dr. Greg Edgecombe. He is an expert in ancient invertebrates at the Natural History Museum in London, in a statement: “Millenniums and centipedes are actually each other’s closest relatives.”

Through fossils and tread-like tracks left by arthropods, scientists determined that this massive creature lived between 290 million and 346 million years ago in what is now North America and Europe — and was just one of many giants roaming the planet.

The abundance of oxygen in the atmosphere has caused creatures such as scorpions and now-extinct dragonfly-like insects called griffinalis to reach enormous sizes that dwarf their modern counterparts, the study authors said. But the arthropods are still notable, reaching roughly the same length as modern crocodiles, said Mikael Lheriter, the study’s lead author.

Leritier is pursuing a doctorate in thousands of ancient legs, A group of arthropods that includes millipedes and centipedes, at the French University Claude Bernard Lyon 1 to understand how arthropods adapted to live on land millions of years ago.

Once the animals died and were buried in layers of sediment over time, some became buried in a mineral known as siderite, which hardened and formed nodules around the remains. Becoming encased in stone has helped preserve the more delicate aspects of the fossilized creatures.

Such nodules were first observed in a coal mine in Montceau-les-Mines, France, in the 1970s, and were then transferred to the collections of a French museum.

“Traditionally, we would section the nodules and take casts of the samples,” Edgecombe said. “These days, we can investigate them through scans. We used a combination of microCT and synchrotron images to examine the arthropods from the inside, revealing the finer details of their anatomy.

3D scans revealed two nearly complete specimens of arthropods that lived 300 million years ago. Both fossilized animals still had most of their legs, and one had a complete head, including antennae, eyes, lower jaws and feeding organs, the first articulated head ever documented, Leritaire said.

The team was surprised to discover that Arthrorpleura had physical characteristics seen in modern millipedes, such as two pairs of legs for each body segment, as well as head characteristics of early centipedes, such as the position of its lower jaw and the shape of its feeding apparatus. The creature also had stalking eyes, like a crustacean, Leritaire said.

In addition to helping researchers better understand what arthropods looked like, the discovery also draws a closer evolutionary relationship between modern millipedes and centipedes.

Previously, scientists thought the two arthropods were distantly related, but in recent years, genetic studies have shown that millipedes and centipedes were more closely related.

“This new scenario has been[criticized]on the grounds that there is no ‘fossil’ or anatomical argument to defend this grouping, but our new findings on arthropods that combine features of both groups tend to confirm this new scenario,” Leritaire wrote in an article. . Email.

Researchers believe the two Arthropleura fossils are very young, measuring only 0.9 inches (25 mm) and 1.5 inches (40 mm) long.

Studies of arthropod specimens have shown that animals vary in the amount of body parts they have, similar to most millipedes that add body parts until they reach a fixed maximum. But centipedes have all their body parts already in place at birth, according to the study authors.

This result suggests that arthropods reach peak segmentation at adulthood, rather than at birth. But researchers are curious to determine whether they have found true specimens, or a previously unknown smaller species, as well as the growth rate over time of such an animal.

“Traces found elsewhere at Montceux-les-Mines suggest that these arthropods were probably about 40 cm (1.3 feet) long at their longest,” Edgecombe said. “Although there is no indication that it could not be larger, we currently have no evidence of that.”

What Arthropleura ate and other secrets

Now that researchers have discovered a complete arthropod head, they hope the discovery will help them solve other mysteries about the giant animal, including what it eats and how it breathes. But other fossils must be found that preserve additional aspects of the arthropod’s body, including the head of an adult.

“While specific intestinal contents have not yet been found, other details about these fossils contribute to the ongoing debate about arthropod diet,” Edgecombe said. “They do not have any fangs or venom (specialized) legs for catching prey, which suggests they were probably not a predator. Since their legs are better suited for slow movement, they were probably more like the detritivorous millipedes living today.”

Leritaire, who studies another group of thousands of ancient legs that may have been amphibious, said he was curious about Arthropleura’s stalking eyes.

“Today, stalked eyes are a typical feature of aquatic arthropods such as crabs or shrimp,” he said. “Could this mean that arthropods were amphibious? To answer this, we need to find the respiratory system of arthropods. Finding these organs can help us (understand) Association of arthropods with water. Gills like in crustaceans may mean an aquatic/amphibian lifestyle, while tracheas (like insects or other millipedes) or lungs (like spiders) mean a terrestrial lifestyle.

But revealing what Arthropleura’s head looked like solves a major mystery, said James C. Lumsdale, associate professor of geology at West Virginia University in a study Related article Which appeared in the progress of science. Lumsdale was not involved in the new study.

“(These) fascinating findings, based on two nearly complete juvenile individuals, provide a new perspective on this enigmatic arthropod,” Lumsdale wrote.

“(T)he most exciting discovery comes from the heads of the specimens bearing a mosaic of characteristics of millipedes and centipedes. …With the mystery of the connections between the largest known arthropods unraveled, the work of reconstructing the life history of this extraordinary creature can finally begin.”