Arthropleura: The Titan of the Carboniferous

Artists reconstruction of the Carboniferous Titan Arthropleura
Image Credit: Nobu Tamara, http://spinops.blogspot.com/

One day, two executives at Warner Brothers film studio are sitting in their office with their heads in their hands. The last film has massively under-performed at the box office, the writers are struggling for ideas, A-List actors are turning their noses up at working for them and their film sets are so quiet you can hear the crickets chirping. However there is a knock at the door. “Come in!” shouts one of the executives. A nerdy looking man; wearing a shirt with an otter on the front, sport shorts that don’t match his top and sandals of a hideous brown and orange colour, steps in to the room. “Hello Brothers Warner! I have a script I’ve written for a potential film, its a mix of Sci-Fi and horror” he exclaims confidently. One of the executives sighs “alright, lets see it”. “Can’t possibly be worse than what we’ve just put out” the other remarks. The executives flick through the script, reading the tale of an adventurer hacking her way through the lush forest of a strange, almost alien world. The adventurer encounters plenty of dangers; ducking a dragonfly the size of an eagle dive-bombing for her head, narrowly dodging the thrusting stinger of an ambushing scorpion the size of a large house-cat and throughout the film she is pursued by a large, unknown monster. At the films climax the adventurer, remarking that she had seen it all now, stumbles on what seems like a large log. She turns round and watches in horror as the log rises and squirms. The monster is revealed! It is a millipede, which rears up high enough to meet her eyes. It hisses, ready to lunge!

“Wow! This script has serious promise! even if it is a little cheesy” One of the executives gasps. “But where is it set?” The other enquires. “Oh turn to the last page!” The geek squeals excitedly. The executives do so, and see the words that would mark the twist ending to this film.

Earth. 300 Million Years Ago.

It sounds absurd, but believe it or not 300 Million years ago planet earth was home to these enormous arthropods. Meganuera and Pulmonoscorpius, the dragonfly and scorpion in our geek’s story, are both fascinating animals. However the most striking of these arthropods, and the one that I have a personal story of, is our monstrous millipede, which has the scientific name Arthropleura, meaning “jointed ribs”.

First discovered in 1854 by Jordan & Meyer, there are two known species of Arthropleura. While the smaller species was only a quarter of a metre in length the larger species was the biggest terrestrial arthropod of all time. Measuring just over two and a half metres long and nearly half a metre wide it was a size that modern millipedes could only dream of. It had a body plan of 30 jointed segments and each segment was covered by a relatively thin armour plating. Its large size meant that it would have had few natural predators (unless one of the large amphibians of the time got in a lucky shot). Since its discovery the main controversy surrounding Arthropleura was whether it was related to millipedes or centipedes, and as a result whether it was a herbivore or a carnivore. This is due to no mouth-parts having been found as of yet. While remains of giant club mosses had been found in some fossil remains a relatively recent study by Kraus showed that this was actually the shed skin of an Arthropleura that had been deposited on top of these club moss fragments. However despite this the common consensus at the moment is that it is a millipede relative and as such a herbivore, feeding on dead plant matter like modern millipedes do today (although its jaws would have given you a bad bite!). Arthropleura first evolved around 315 million years ago and went extinct 299 million years ago. The main reasons for its extinction being a combination of the disappearance of the coal swamps that it resided in and reduction in oxygen levels.

A fossil of the armour plates of Arthropleura from the Senckenberg Museum of Frankfurt in Germany. Image Credit: Ghedoghedo, https://commons.m.wikimedia.org/wiki/File:Arthropleura_armata.jpg

Unfortunately such an animal really was a product of its time. Arthropleura and other arthropods could only grow to such a size because of the special environment conditions present during the Carboniferous period. The earth had a much higher concentration of oxygen compared to modern times (almost 35%, compared to about 21% today). This suited arthropods in particular as it meant that they could take in more oxygen and therefore have more energy via respiration to use in growth. Arthropods take in oxygen via tiny tubes on the side of their bodies, known as trachea, or even directly through their skin. This system is nowhere near as efficient as true lungs are in terrestrial vertebrates. As a result the lower oxygen levels of today means that arthropods simply can’t get enough energy from respiration to maintain such large sizes. If Arthropleura was alive today it would not be able to survive in such a low oxygen environment. However a large concentration of oxygen isn’t the sole reason for their size, as a lack of competition and predation could also have helped.

Fossilised tracks of Arthropleura such as these are found in places in Scotland (e.g. the Island of Arran) and the USA. Image Credit: Ashley Dace, https://www.geograph.org.uk/photo/1994274

To finish this blog i’m going to share my personal encounter with an Arthropleura! Or rather, its fossilised tracks. When I was around the age of 11, during a family holiday in Scotland, I went to see the Arthropleura tracks at Crail. My young palaeontology mad self loved seeing these tracks, and there is a photo that proves it. So as it turns out this animal is indeed Scottish! (well half-Scottish technically, as fossils and trackways have also been found in the USA, but I like to think its Scottish). Arthropleura tracks are also a famous attraction of the island of Arran in Scotland. Whilst I did go to Arran during the first year of my university degree sadly my group didn’t have time to go see them.

So Arthropleura is yet another example of the weird creatures that evolution has produced, and a true marvel of the distant past. In my humble opinion, it would make a fantastic movie monster!

References/Further Reading

A great blog on Arthropleura written by Hans-Dieter Sues, a Paleontologist based at the National Museum of Natural History in Washington DC. The blog was published on National Geographic

Sues, Hans-Dieter,”Largest Land-Dwelling “Bug” of All Time”, National Geographic, Jan. 15, 2011, blog.nationalgeographic.org/2011/01/15/largest-land-dwelling-bug-of-all-time/

A blog, published on National Geographic, which gives futher background on the Carboniferous Period

National Geographic, “Carboniferous Period”, National Geographic, nationalgeographic.com/science/prehistoric-world/carboniferous/

A paper from 1992, written by Paul Pearson (Pearson 1992) and published in the Scottish Journal of Geology describing Arthropleura tracks (named Diplichnites cuithensis) from Fife, Scotland

Pearson, P. N. (1992). “Walking traces of the giant myriapod Arthropleura from the Strathclyde Group (Lower Carboniferous) of Fife.” Scottish Journal of Geology 28(2): 127-133.

Another paper, written by Ronald Martino & Stephen Greb (Martino & Greb 2009) and published in Journal of Paleontology, describing a set of Arthropleura tracks, this time from Kentucky, USA

Martino, R., & Greb, S. (2009). Walking trails of the giant terrestrial arthropod Arthropleura from the Upper Carboniferous of Kentucky. Journal of Paleontology, 83(1), 140-146. doi:10.1017/S0022336000058200

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