| Arthropleuridea | |
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| Arthropleura fossil illustration | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Myriapoda |
| Class: | Diplopoda |
| Subclass: | †Arthropleuridea Waterlot, 1934 |
| Orders | |
Arthropleuridea is an extinct subclass ofmyriapodarthropods that flourished during theCarboniferous period, having first arisen during theSilurian, and perishing in theEarly Permian.[1] Members are characterized by possessing diplosegement (fused "double segments", as in modern-daymillipedes)paranotal tergal lobes separated from the body axis by a suture, and bysclerotized plates buttressing the leg insertions. Despite their unique features, recentphylogenetic research suggests Arthropleuridea be included among millipedes in the class Diplopoda.[2][3] The subclass contains three or two recognizedorders, each with a singlegenus.[4]
Arthropleurids lived in the moistcoal swamps that were common at the time and may haveburrowed in the undergrowth. They were eitherherbivores ordetritivores. Besides their size, their most distinguishing features were their legs with eight segments (as many as 30 pairs) and extremely toughexoskeletons. There is no evidence ofspiracles, so the animals must have usedlungs orgills forrespiration.[3]
Most arthropleurideans are thought to have been terrestrial, although, without any known respiratory structure, terrestriality is assumed only by analogy to modern arthropods.[5] Early forms, however, includingEoarthropleura (order Eoarthropleurida), appear to have beenaquatic.[citation needed] For this reason, some question Arthropleuridea's inclusion among millipedes because no modern aquaticmyriapods are known.[3]
Arthropleuridea is most famous forArthropleura (order Arthropleurida).Tracks fromArthropleura up to 50 cm wide have been found atJoggins, Nova Scotia.[6] Reaching over 2 meters in length, arthropleurids are among the largestarthropods ever to have lived. The lack of large terrestrial vertebrate predators and the highlyoxygenic atmosphere at that time probably enabled them to grow so large.[7] It was previously believed thatArthropleura becameextinct as the coal swamps dried out.[3] However, many fossils have been discovered after theCarboniferous rainforest collapse. A more recent proposal is that predation bytetrapods and thearidification of theequator caused it to become extinct.[1][8]Arthropleura has been found from the UpperCarboniferous ofEurope andNorth America.
Eoarthropleura has been found from the Upper Silurian through the UpperDevonian ofEurope andNorth America.[9]
Microdecemplex, of the order Microdecemplicida, was dwarfed by the other Arthropleurideans, at just a few millimeters long. The genus is known from the Middle through UpperDevonian ofNew York state, USA.[4] This genus, however, is suggested to reject from Arthropleuridea after research of well-preserved specimen ofArthropleura.[10]
After several decades of uncertainty, Arthropleuridea was placed within the Diplopoda in the year 2000.[11] However, there is still controversy regarding the relationships of the three orders to living millipede groups.[2][12] Some authors place Arthropleuridea within theChilognatha, as asister group to all living Chilognathan millipedes (Pentazonia +Helminthomorpha).[11][13] An alternate hypothesis breaks up the subclass: placing the orders Arthropleurida and Eoarthropleurida within thebasalPenicillata (as sister to the livingPolyxenida), and leaving only Microdecemplicida as a sister group to the living Chilognatha.[14] Under this hypothesis, Arthropleuridea would beparaphyletic.
Orders of the classDiplopoda(millipedes) | |||||||||||||||||||||||||||||||||
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