|Name Meaning||Jointed Ribs||Width||50–55 centimeters (19.7–21.7 inches)|
|Pronunciation||Ar-thro-plew-ra||Length||2.5–2.63 meters (8.2–8.62 feet)|
|Era||Paleozoic, Carboniferous–Permian Period||Weight||50 kilograms (110.2 pounds)|
|Classification||Arthropoda, Myriapoda & Diplopoda||Location||North America, Europe|
If you think that the millipede occasionally walking on the walls of your room is disgusting and quite large, you’ll reconsider this thought once you hear about the prehistoric Arthropleura!
The Arthropleura, also known as the jointed ribs, inhabited our planet 345-290 million years ago.
It was a giant millipede that could grow as long as a car! Just imagine how many legs it had!
This large arthropod lived in the territories of today’s North America and Europe and is now considered the world’s largest invertebrate.
The genus was described primarily from exuviae (the remains of an exoskeleton that fossilized upon molting) and fossil trackway.
Today, the Arthropleura genus consists of five species, but the specific differences between them remain unknown.
The Arthropleura was similar in appearance to modern millipedes, except that it was much larger.
In short, it had a segmented body and many legs.
But why did it grow so large? What habitat did it live in? And how did it reproduce?
Keep reading to discover the details!
The Arthropleura was a large millipede arthropod.
It is often regarded as one of the largest known land invertebrates, reaching 2.5 meters (8.2 feet) in length!
Additionally, it was as thick as 50–55 centimeters (19.7–21.7 inches).
Compared to the largest extant millipede, the giant African millipede, scientifically known as Archispirostreptus gigas, which grows only up to 33.5 centimeters (13.2 inches) in length and 6.7 centimeters (2.6 inches) in width, the Arthropleura was undoubtedly a giant!
The size of Arthropleura is also typically compared to that of the Jaeokelopterus, a predatory eurypterid or sea scorpion now believed to be the largest known arthropod, likely reaching 2.59 meters (8.5 feet) in length.
However, if we consider other studies that indicate that an Arthropleura specimen may have measured 2.63 meters (8.62 feet) long and weighed 50 kilograms (pounds), we may even say it surpassed the Jaeokelopterus in size!
The Arthropleura likely had an invisible head hidden underneath the first body segment.
The head may have been equipped with some antennae and trumpet-like organs.
The number of trilobate tergites (segments) probably ranged from 28 to 32, and each tergite likely had two pairs of legs, as observed in extant millipedes.
In short, the Arthropleura resembled extant millipedes in having a long, narrow body composed of numerous segments and multiple legs.
Habitat and Distribution
Arthropleura fossils were unearthed from multiple localities in North America and Europe. The genus is also known from fossil tracks.
Some sources list the Arthropleura as a common prehistoric invertebrate in the United States, Canada, France, Scotland, Belgium, Germany, the Czech Republic, and the United Kingdom.
Studies on its tracks show that the preferred habitat of the Arthropleura was likely filled with water sources and rich in vegetation that subsequently turned into coal deposits.
It has been historically thought that the Arthropleura could survive only in coal forests, meaning wetlands that covered tropical land areas.
Later studies confirmed that the Arthropleura could also live in open areas.
The territory the Arthropleura walked on probably depended on each individual’s age.
For example, juveniles not longer than 0.15 meters (0.5 feet) may have walked on muddy substrates, while adults probably avoided it.
The young may have started moving on sandy substrates once they reached 0.8 meters (2.6 feet) long.
If they moved on sandy substrates until then, no tracks would be left, as they wouldn’t be heavy enough.
These discoveries show that juveniles and adults may have preferred different habitats, so suggesting a typical Arthropleura environment would be difficult.
Moreover, since this creature has been confirmed to have such a wide distribution, its habitat likely differs slightly depending on the location.
Behavior and Diet
Although not much is known about the particular behavior of Arthropleura invertebrates, we can assume they spent much of their lives walking around looking for food.
On the other hand, they definitely did not barge into people’s houses, terrifying them, as extant millipedes do!
Some studies show that the Arthropleura ate fruits, sporophylls, seeds, and possibly spores.
However, scientists question this theory, as they’re not sure these foods were nutritious enough for such large invertebrates.
Moreover, they were only seasonally available.
As such, they do not rule out the possibility that the Arthropleura could have been an omnivore and, thus, a predator preying on other prehistoric creatures like the contemporary eryopids.
However, until fossilized gut contents and mouth parts are found, the true diet of the Arthropleura will remain a mystery.
Modern millipedes are known to be quite defenseless; they are not fast and can’t bite or sting.
As such, they rely on the only defense mechanism mother nature gifted them: the ability to curl into a tight coil, thus hiding the legs inside the exoskeleton.
While this behavior has not been confirmed for the Arthropleura, we may assume it may have been more difficult for it to curl into a tight coil considering its size, although it probably possessed a similar defense mechanism.
On the other hand, did it actually require a defense mechanism? After all, some scientists believe it had no predators!
While other prehistoric creatures are quite well known in terms of their reproductive behavior, there’s little to no information about an Arthropleura’s life cycle.
We can guess some characteristics and behaviors if we analyze what is known about the reproductive behavior and growth rates of modern millipedes.
Obviously, many things may have changed over the last 290 million years since the Arthropleura went extinct, but we can at least outline possible habits.
The genital openings of millipedes are located near the second pair of legs, on the underside of the third body segment.
Before copulation, male millipedes may engage in some kind of courtship ritual.
Modern millipedes are known to have developed different mating styles and structures.
For example, some rely on indirect mating, when males first deposit the spermatophores and the females pick them up.
Others rely on direct copulation, during which males use specialized appendages called gonopods to transfer the sperm directly to the female by inserting the gonopods into her.
The gonopods’ shape, size, and location differ between species.
After mating, females can lay up to 300 eggs at a time.
Some species lay the eggs directly on moist soil, while others construct nests using dried feces.
The extent of parental care exhibited depends on the species; some abandon the eggs right after laying them, while others care for both the eggs and the young.
Baby millipedes hatch with only three pairs of legs.
The other four segments have no legs, and as they grow, they add new segments and leg pairs.
They also molt repeatedly.
A millipede’s lifespan has been estimated at 1–10 years, and this depends on the species.
How many of these details can be attributed to the Arthropleura? It remains unknown.
However, we cannot rule out the possibility that at least some behaviors are valid for the extinct genus as well!
Now you’re probably wondering why Arthropleura creatures grew so large and extant millipedes are so small.
We don’t mind them being small, but there must be an explanation!
The truth is that the environment during the Carboniferous was richer in oxygen.
This allowed the Arthropleura to grow much larger than its ancestors.
Over time, the oxygen levels lowered, and its successors grew smaller.
Evolution and History
The Arthropleura is classified under the Arthropleuridae subclass in the Diplopoda class of millipedes.
These invertebrates are widely recognized as the first animals to colonize land 440 million years ago, during the Silurian.
Back then, millipedes fed on mosses and vascular plants.
The earliest forms are considered Kampecaris obanensis and members of the Archidesmus genus.
More than 400 million years ago, these invertebrates were much smaller, measuring only 20–30 millimeters (0.8–1.2 inches) long.
The appearance of the Arthropleura marked a significant event in its evolutionary history, as the members of this genus became the largest known invertebrates and members of the Diplopoda class.
Interactions with Other Species
Modern millipedes are known to engage in mutualistic relationships (interactions between two or more species where all benefit from them) and commensal relationships (interactions between two species where only one species benefits from them).
Some millipede species are known to be close to ants and mites.
This is an indicator that millipedes are relatively social creatures.
Were prehistoric millipedes just as social? It remains unknown.
However, since the Carboniferous and the Permian were rich in insects, arachnids, and myriapods, they may have engaged in a certain degree of interaction.
Tetrapods, synapsids, and amphibians were also quite common back then.
The discovery of the Arthropleura genus carries significant paleontological information, as it marks a turning point in the evolution of arthropods and millipedes in particular.
Being the largest millipede ever known, it’s no wonder the Arthropleura caught the attention of both scientists and wildlife enthusiasts.
It is enough to imagine such a gigantic millipede to be either impressed or terrified by its size!
If you’re a true wildlife enthusiast, you should watch the Walking with Monsters documentary, as the Arthropleura appears in the second episode.
It is also a character in Prehistoric Park and Primeval.
The Arthropleura is a gigantic prehistoric millipede arthropod.
It was widespread across North America and Europe during the Carboniferous and Permian.
More precisely, it was alive for roughly 55 million years, between 345 and 290 million years ago, from the Visean until the Sakmarian.
It is now considered the largest invertebrate known, reaching approximately 2.5 meters (8.2 feet) in length, although others may have been even longer.
Its diet remains unknown, as scientists aren’t entirely sure whether this multi-legged creature was herbivorous, detritivorous, or omnivorous.
Hopefully, future paleontological findings will shed light on other aspects of the Arthropleura’s appearance, lifestyle, and behavior.
Why did Arthropleura go extinct?
The exact reason behind the Arthropleura extinction is unknown.
Some scientists associate it with the diversification of tetrapods, while others suggest that the climatic changes during the Permian didn’t support its existence anymore.
Its extinction has been historically associated with the Carboniferous rainforest collapse, which led to the decline of coal forests.
But since fossils were discovered after this event, the theory was subsequently disapproved of.
How did the Arthropleura breathe?
The Arthropleura probably had no tracheal system, as scientists couldn’t find any traces confirming otherwise.
As such, it was suggested that each body segment had paired, pocket-like structures on the underside.
This was covered by a thin layer of air that allowed oxygen absorption.
This arthropod could breathe more easily since the oxygen levels were much higher when the Arthropleura was alive (35% compared to today’s 21%).