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Not to be confused with Anthopleura.

Prehistorica CM/sandbox
Temporal range: Early Viséan-Sakmarian, 346–290 Ma [1]
Arthropleura sp., juvenile specimen from Montceau-les-Mines (France)
Reconstruction of Arthropleura based on Montceau-les-Mines fossils
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Myriapoda
Class: Diplopoda
Subclass: †Arthropleuridea
Order: †Arthropleurida
Waterlot, 1933
Family: †Arthropleuridae
Zittel, 1885
Genus: †Arthropleura
Meyer, 1854
Species[2]
  • A. armata Meyer, 1854
  • A. mammata Salter, 1863
  • A. fayoli Boule, 1893
  • A. britannica Andrée, 1910
  • A. maillieuxi Pruvost, 1930
  • A. cristata Richardson, 1959
Synonyms
  • A. affinis Goldenberg, 1873
  • A. zeilleri Boule, 1893
  • A. moyseyi? Calman, 1914

Arthropleura (Greek for 'jointed ribs') is a genus of massive myriapod that lived in what is now Europe and North America around 345 to 290 million years ago,[2][3] from the Viséan stage of the lower Carboniferous Period to the Sakmarian stage of the lower Permian Period.[2][4] It is related to millipedes, and was capable of reaching at least 2 metres (6 ft 7 in) in length, possibly up to over 2.5 metres (8 ft 2 in), making it the largest known land arthropod of all time. Arthropleura is known from body fossils as well as trace fossils, particularly giant trackways up to 50 centimetres (20 in) wide, and potentially also large burrows. It lived in open, sparsely wooded environments near water, and was likely semi-aquatic.[1][2]

History and classification

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A nearly complete juvenile found by Dr. Lewis Moysey, ascribed by Waterlot to Arthropleura aramata (previously A. moyseyi), showing the first known fossil of the head. This specimen was also said to preserve fragments of lycopod plants in the gut. From Calman (1914)
 
 
Photographs of Arthropleura armata (Figs. 1-12) and Arthropleura mammata (Fig. 13) fossils, from Andree (1910).

First discovered in 1854, Arthropleura has consistently attracted much artistic and scientific attention, yet has historically been known from mostly fragmentary remains.[5] Prior to its description, the remains were attributed by Jordan and Meyer to a decapod crustacean. In their subsequent description of the genus, they compared it with trilobites and eurypterids. Another author, Moritz Kliver, described a small specimen of Arthropleura armata showing the underside, with a series of 7 pairs of limbs articulated with various other plates, including the sternites. Kliver that Arthropleura could not be an insect, arachnid, or myriapod, but instead that it was a non-decapod crustacean, comparing the appendages to those of branchiopods. Following authors tended to view Arthropleura in connection to isopods, some believing it represented a very primitive Eumalacostracan crusteacean. Palaeontologists Lewis Moysey and Henry Woodward were the first to associate Arthropleura with Myriapoda in 1911.[6]

Gérard Waterlot published a landmark study in 1934, establishing the order Arthropleurida, placing the group as sister to order Trilobita, within the defunct crustacean subclass Archaeocrustacea. He believed the limbs to be composed of two branches, a lower walking leg and an upper gill branch, like the biramous limbs of trilobites. Palaeontologist Leif Størmer remarked on this study in 1944, writing that after careful study of the photographs, the supposed two branches of the limb are always found close together, close enough that even their joints consistently line up. Because of this, he interpreted the limbs as uniramous, having only a single branch. Waterlot referred a nearly complete juvenile specimen described by Dr. W. T. Calman as Arthropleura moyseyi[7] to Arthropleura armata, and agreed that this specimen showed the mostly unknown head segment of the animal. A curved structure found along the edge of the head resembled the mandibles of some myraipods, and so it was seen by Waterlot as a cephalic feeding appendage, and that this meant Arthropleura was carnivorous, feeding on small soft-bodied prey. Waterlot also believed that Arthropleura was amphibious, living at the bottom of lakebeds, with occasional excursions onto the land where the humidity of coal swamps allowed it to continue breathing with its supposedly trilobite-like gills. Other authors preferred a terrestrial habitat, and questioned the carnivorous diet.[6] The juvenile specimen described by Waterlot appeared to show various plant remains within the gut tract, more recently this has been seen as a taphonomic artifact.[1]

Arthropleura as a myriapod or relative of myriapods (particularly diplopods) becaming the prevailing view among scientists in the following decades,[6] and the limbs became quite well understood.[8] Further species of Arthropleura have been described over the decades, mostly from central Europe and the UK, and even from the central United States with Arthropleura cristata. The head segment, however, remained enigmatic even into the 21st century. What had previously been identified as the head was reinterpreted as the collum, the first segment behind the head, with the true head hidden beneath it.[5] The millipede Microdecemplex was described in 1999, and was believed to belong to the subclass Arthropleuridea. Thse tiny fossils were much more complete, and so its head anatomy was taken as an insight into the head of Arthropleura.[9]

Finally, in 2024, exceptionally preserved fossils from the Montceau-les-Mines Lagerstätte of France were studied and described with the aid of Micro-CT scanning, revealing the head region in two nearly complete juvenile Arthropleura fossils.[1] They showed that the head identified by past authors was indeed the head, with the collum a thin segment behind it. Waterlot's cephalic limbs are now identified as paired ventral scleites, protecting the head like a car bumper. The cephalic limbs showed two pairs of external maxillae, and an internal set of mandibles. Phylogenetic analysis found Arthropleura just outside of Diplopoda (stem-group Diplopoda), while Microdecemplex was found as a crown-group millipede rather than an arthropleuridean.

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    The larger of two exceptionally preserved Arthropleura fossils from Montceau-les-Mines (France), showing the head region (including the antennae and stalked eyes), as well as legs (two pairs per body segment), from Lhéritier et al. (2024).[1]
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    Detail of the previous fossil, showing the head in greater resolution, from Lhéritier et al. (2024).[1]
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    The smaller of the two exceptionally preserved Arthropleura fossils from Montceau-les-Mines, also showing the head region, from Lhéritier et al. (2024).[1]
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    Detail of the smaller of two exceptionally preserved Arthropleura fossils from Montceau-les-Mines (France), showing the head region (including the antennae and stalked eyes), from Lhéritier et al. (2024).[1]

Morphology

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Arthropleura armata grew to be up to 2.5 metres (8 ft 2 in) long.[10] Tracks from Arthropleura up to 50 centimetres (20 in) wide have been found at Joggins, Nova Scotia.[11] In 2021 a fossil, probably a shed exoskeleton (exuviae) of an Arthropleura, was reported with an estimated width of 55 centimetres (22 in), length of 1.9 metres (6 ft 3 in) to 2.63 metres (8 ft 8 in) and body mass of 50 kg (110 lb).[3][2] It is one of the largest arthropods ever known, as large as the eurypterid Jaekelopterus rhenaniae, whose length is estimated at 2.33–2.59 metres (7 ft 8 in – 8 ft 6 in).[12] The 2024 study reported the complete head and trunk of a juvenile specimen of Arthropleura sp. (MNHN.F.SOT002123) from Kasimovian (~305 Ma) Montceau-les-Mines lagerstätte, which revealed multiple previously unknown features.[1] Arthropleura had large, flattened ventral sclerites and a pair of antennae with at least seven antennal articles at the front of its head.[1] The trunk anatomy of Arthropleura is characterized by a series of well-developed 28-32 tergites (dorsal exoskeleton)[2] having three lobes like a trilobite, the dorsal surface of which is typically covered by many tubercles or spines.[1] Juvenile specimens have fewer numbers of tergites at 20-24, suggesting hemianamorphic development, with the number of segments reaching their maximum number (adding during each moult) before the final moult, the animal continuing to grow while retaining the same number of segments past a certain point.[1]

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    Diagrammatic reconstruction of A. armata
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    Anterior morphology of A. armata, with details of the head drawn from A. sp. from Montceau-les-Mines
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    Leg and associated structures of A. armata
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    Size estimation of the largest specimen of Arthropleura

Arthropleura had two pairs of maxillae appendages beneath the head, each composed of 3 segments, the outermost pair of maxillae being relatively large and pointed. These outwardly resemble the forcipules of centipedes, but were incapable of delivering venom. The paired mandibles were small, composed of three segments, and fully internalized into the head, similar to centipedes rather than millipedes. The antennae and mandibles identify it as a millipede, but the presence of a pair of legs on its collum, which is absent in present day species, reveals it as the sister group of the millipede crown group. Unlike any living myriapods, they had stalked compound eyes, which despite also being known from the extinct myriapod group Euthycarcinoidea, appears to be a derived trait evolved independently from the euthycarcinoids.[1][13] Each body segment bore two pairs of walking legs, which themselves are composed of 9 or 10 segments (podomeres). A crease ran down each side of the leg which probably allowed for stronger muscle attachment,[14] and the ventral surface bore paired endites on each segment. The anterior surface of the leg was smooth, while the posterior surface was tuberculate, with many pores that probably housed setae. Around each walking leg pair, there were three pairs of ventral plates located alongside the median sternite, namely K-plates, B-plates, and rosette plates, and either the B-plates or K-plates were thought to be respiratory organs[15][16]. This has however also been questioned, with Rolfe and Ingham (1967) considering all of these plates to be simply sclerotized ventral integument responsible for reinforcing and buttressing the limb bases to enable locomotion for such a large animal. Their placement infront of the limb also suggests the legs would thrust backward and downward during movement, before returning to their standard position, with little capacity for movement forward.[8] The body terminated with a trapezoidal telson.[17]

 
Tubercule patterns of different Arthropleura species, from Lhéritier et al. (2024).[1] The Montceau species is only identified at the genus-level and not assigned to a species name, though it almost certaintly represents a new species.

The different species of Arthropleura are primarily differentiated by the dorsal ornamentation of their tergites. There is a keel across the middle of the tergites running laterally in all species, and typically, there is a line of large tubercules running behind it. The only exception is A. cristata from the Mazon Creek of the United States, where tuberculate ornamentation is absent. Because complete specimens are rare, species are sometimes poorly delineated, and could possibly represent different growth stages of the a smaller number of species, leading paleontologists who work with Arthropleura to often only give a genus-level identification to the fossils. The Montceau-les-Mines species (known from only juvenile specimens) has a band of 4 large tubercules on the paratergal lobe, which rise up into tall spines. This pattern is extremely similar to A. moyseyi, which suggests that A. moyseyi is also a juvenile, possibly of A. mammata. Because the ornamentation may change over time, it is not viewed as a reliable way to determine species. At Montceau-les-Mines, large specimens are absent, and the largest trackways were left by animals less than 50 centimetres (20 in) in length, so this species may have been genuinely much smaller than the giant species elsewhere in Europe.[1]

Paleobiology

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Fossil footprints of Arthropleura, Laggan Harbour, Isle of Arran, Great Britain. This trail is the type specimen of the ichnospecies Diplichnites cuithensis.

Most fossils of Arthropleura are believed to represent exuviae (moulted shells) instead of carcasses.[16] Arthropleura has typically been reconstructed living in coal swamps, based on the co-occurence of its fossils with dense plant remains and coal veins. However, this view is no longer strictly supported. Many fossils of Arthropleura are found either before or after the dominance of such coal forests, and direct geological and paleobotanical evidence suggests its primary habitat was far more open. Arthropleura preferred open environments, particularly sparsely wooded and near to water, such as coastlines and floodplains. Arthropleura is also found in association with tetrapod trackways suggesting they lived in the same environments. In addition to large trackways, enormous burrows have been attributed to Arthropleura and arthropleurids generally, suggested to be made during periods of Aestivation similar to hibernation. Arthropleura remains (body fossils and trackways) are also closely associated with the palaeoequator, with all documented fossils occuring with 10° of either side of the palaeoequator during both the Carboniferous and Permian.[2]

Arthropleura has repeatedly been suggested to have been amphibious to some degree. Despite falling out of favour for many years, this idea has been bolstered by new evidence. Trackways, often found in association with coastlines, are found in both submerged and emergent substrates, showing that Arthropleura was probably capable of walking in air and in shallow water, and did so accordingly. Additional evidence for this comes from the juvenile Montceau fossils, which demonstrate that the eyes were large and stalked, unlike any living myriapod. This condition is however known in the extinct myriapod family euthycarcinoidea (which Arthropleura is sometimes associated with), which were aquatic to amphibious. The authors suggest that this could point to a semi-aquatic, amphibious lifestyle, capable of entering and exiting shallow bodies of water. It has been suggested that due to their large size, moulting (a stressful period even for smaller arthropods) probably occured underwater, allowing its weight to be supported while its new exoskeleton hardened.[14]

The diet of Arthropleura has also been heavily debated. Waterlot suggested it was a carnivore, but the holotype of "A. moyseyi" was suggested to preserve the original gut contents, a mix of woody plant material, suggesting it was an herbivore.[6] The interpretation of these fossils as gut contents is no longer supported. Currently, Arthropleura is believed to be a detritivore, like most extant millipedes. This means feeding on either dead and decaying plant matter or animal remains when available. The short, closely packed legs, as well as evidence from the morphology of the ichnofossil trackways, both suggest that Arthropleura was a very slow moving animal, and the lack of venomous forcipules or other predatory adapations to the limbs basically precludes a predatory lifestyle.[1]

The giant size of Arthropleura is frequently attributed to higher oxygen levels during the Carboniferous,[18] however, this does not align with the fossil record or modern understanding of arthropod size range. Arthropleura reaches giant sizes before the rise in oxygen concentration during the Carboniferous, with the largest known body fossil found in an interval where oxygen levels were only about 23% higher than modern day. More likely, Arthropleura was capable of gigantism due to other generally favourable environmental and ecological conditions and lack of serious competition. Consequently, Arthropleura went extinct during the early Permian, probably due to the desertification of the equatorial regions of the supercontinent and competition with Permian tetrapods.[2]

See also

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References

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  1. ^ a b c d e f g h i j k l m n o p Lhéritier, M.; Edgecombe, G. D.; Garwood, R. J.; Buisson, A.; Gerbe, A.; Mongiardino Koch, N.; Vannier, J.; Escarguel, G.; Adrien, J.; Fernandez, V.; Bergeret-Medina, A.; Perrier, V. (2024). "Head anatomy and phylogenomics show the Carboniferous giant Arthropleura belonged to a millipede-centipede group". Science Advances. 10 (41). eadp6362. doi:10.1126/sciadv.adp6362.
  2. ^ a b c d e f g h Davies, Neil S.; Garwood, Russell J.; McMahon, William J.; Schneider, Joerg W.; Shillito, Anthony P. (Dec 21, 2021). "The largest arthropod in Earth history: insights from newly discovered Arthropleura remains (Serpukhovian Stainmore Formation, Northumberland, England)". Journal of the Geological Society. 179 (3). doi:10.1144/jgs2021-115. S2CID 245401499.
  3. ^ a b "Largest-ever millipede fossil found on Northumberland beach". BBC News. 21 December 2021. Retrieved 21 December 2021.
  4. ^ Martino, Ronald L.; Greb, Stephen F. (2009). "Walking trails of the giant terrestrial arthropod Arthropleura from the Upper Carboniferous of Kentucky". Journal of Paleontology. 83 (1): 140–146. Bibcode:2009JPal...83..140M. doi:10.1666/08-093R.1.Archived 2019-12-23 at the Wayback Machine.
  5. ^ a b Lamsdell, James C. (11 October 2024). "Bring me the head of Arthropleura". Science Advances. 10 (41). doi:10.1126/sciadv.ads9192. ISSN 2375-2548.
  6. ^ a b c d Glaessner, M. F.; Hoffman, Richard L.; Newman, W. A.; Hahn, Gerhard; Zullo, V. A.; Rolfe, W. D. Ian (1 January 1969). "Part R, Arthropoda 4, vol. 1 & 2, ch. 5, p. 567-629". Treatise on Invertebrate Paleontology: 607–620. doi:10.17161/dt.v0i0.5630.
  7. ^ Calman, W. T. (December 1914). "III.—On Arthropleura Moyseyi , n.sp., from the Coal-Measures of Debyshire". Geological Magazine. 1 (12): 541–544. doi:10.1017/S0016756800153452.
  8. ^ a b Ian Rolfe, W. D.; Ingham, J. K. (January 1967). "Limb structure, affinity and diet of the Carboniferous 'centipede' Arthropleura". Scottish Journal of Geology. 3 (1): 118–124. doi:10.1144/sjg03010118.
  9. ^ Wilson, Heather M.; Shear, William A. (1999). "Microdecemplicida, a new order of minute arthropleurideans (Arthropoda: Myriapoda) from the Devonian of New York State, U.S.A.". Transactions of the Royal Society of Edinburgh: Earth Sciences. 90 (4): 351–375. doi:10.1017/S0263593300002674.
  10. ^ Mcghee, George R. Jr (2013-11-12). When the Invasion of Land Failed: The Legacy of the Devonian Extinctions. Columbia University Press. ISBN 9780231160575.
  11. ^ "The Excitement of Discovery". Virtual Museum of Canada. Archived from the original on February 4, 2012. Retrieved 2006-04-17.
  12. ^ Braddy, Simon J; Poschmann, Markus; Tetlie, O. Erik (2008-02-23). "Giant claw reveals the largest ever arthropod". Biology Letters. 4 (1): 106–109. doi:10.1098/rsbl.2007.0491. PMC 2412931. PMID 18029297.
  13. ^ Bring me the head of Arthropleura
  14. ^ a b Donovan, S. K. (2002). "Arthropleurid Myriapods". Geology Today. 18 (1): 35–37. doi:10.1046/j.1365-2451.2002.00322.x.
  15. ^ Sues, Hans-Dieter. "Largest Land-Dwelling "Bug" of All Time". National Geographic. Ford Cochran. Archived from the original on 4 March 2016. Retrieved 14 February 2017.
  16. ^ a b Schneider, Joerg; Lucas, Spencer; Werneburg, Ralf; Rößler, Ronny (2010-05-01). "Euramerican Late Pennsylvanian/Early Permian arthropleurid/tetrapod associations – implications for the habitat and paleobiology of the largest terrestrial arthropod". New Mexico Museum of Natural History and Science Bulletin. 49: 49–70.
  17. ^ Kraus, O.; Brauckmann, C. (2003-05-05). "Fossil giants and surviving dwarfs. Arthropleurida and Pselaphognatha (Atelocerata, Diplopoda): characters, phylogenetic relationships and construction". Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg. 40: 5–50.
  18. ^ Thom Holmes (2008). "The first land animals". March Onto Land: the Silurian Period to the Middle Triassic Epoch. The Prehistoric Earth. Infobase Publishing. pp. 57–84. ISBN 9780816059591.
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