Thursday 23 August 2018

Permocrassacus novokshonovi and Permocryptops shelleyi: Two new species of Scolopendromorph Centipedes from the Permian of Russia.

Myriapods (Millipedes and Centipedes) are well represented in the fossil records of the Devonian and Carboniferous, but almost totally absent in that of the Permian, and quite rare in Mesozoic deposits, only becoming common on again in post-Cretaceous amber deposits. This is somewhat frustrating for palaeontologists who study the group, as almost all of the Devonian and Carboniferous fossils belong to extinct Millipede lineages, whereas most of the Mesozoic specimens belong to living groups, suggesting that these groups evolved either in the Permian or the Triassic.

In a paper published in the journal Acta Palaeontologica Polonica on 29 June 2018, Alexander Khramov of the Borissiak Paleontological Institute of Russian Academy of Sciences, and the Cherepovets State University, William Shear of Hampden-Sydney College, Randy Mercurio of the Engineering and Science Division at the Eastern Research Group, Inc., and Dmitry Kopylov, also of the Borissiak Paleontological Institute of Russian Academy of Sciences, and the Cherepovets State University, describe two new species of Scolopendromorph Centipedes from Permian deposits in Russia.

Scolopendromorph Centipedes include the largest known Myriapods today, and some of the largest Arthropods of any type, with some tropical species reaching over 30 cm in length and being feared for their highly toxic venom. Most species, however, are much smaller and many are found in temperate climates. All Scolopendromorphs, unfortunately, live in soil and leaf-litter habitats where there are numerous bacteria and fungi capable of digesting both chitin and the other proteins that make up arthropod cuticle, which, since they lack any mineralized tissues, gives them a very low chance of entering the fossil record. There have only been five previously reported fossil Scolopendromorphs from Palaeozoic and Mesozoic deposits, two from the Carboniferous Mazon Creek Lagerstätte of Illinois and three from the Crato deposits of Brazil.

The first new species described is named Permocrassacus novokshonovi, where 'Permocrassacus' refers to the Permian origin of the fossil and the encrassate (enlarged) nature of the last pair of legs of the specimen, and 'novokshonovi' honours Russian palaeoentomologist Viktor Novokshonov (1966–2003), for his work on the Tshekarda fossil site in the Perm Krai of Russia, where the specimen from which the species is described was discovered. The specimen is a 38 mm long Cenipede with 21 pedigerous (leg-bearing) segments, the last of which bears a greatly enlarged pair of legs, preserved on a split block as part and counter-part on a split slab from the Koshelevka Formation.

Scolopendromorph Chilopod Permocrassacus novokshonovi, from the Tshekarda locality, lower Permian of Russia. (A), (B) General view of part and counterpart, respectively. (C) Drawing compiled from part and counterpart. (D Head, antenna, and 1st leg. (E) Pairs of 20th and ultimate legs. Numbers indicate segments of trunk or legpairs. Khramov et al. (2018).

Enlarged final leg pairs are a feature of several modern groups of Scolopendromorph Centipedes. The final legs of the Cryptopidae are highly elongated, but no thicker than the other legs, those of the Scolopendridae are both elongate ans thickened, while those of the Plutoniumidae have been modified to form a large pair of forceps. Khramov et al. do not feel confident enough to assign Permocrassacus novokshonovi to any of these modern groups, but suggest that it may represent an intermediate state between the enlarged rear legs of the Scolopendridae and the forceps of the Plutoniumidae.

The second new species described is named Permocryptops shelleyi, where 'Permocryptops' derives from Permian and the modern Scolopendromorph  Family Scolopocryptopidae, which the specimen resembles. The species is described from a single specimen preserved as part and counterpart on a spilt block from the Poldarsa Formation at Isady in the Vologda Oblast of Russia. The specimen preserves last 12 segments of the body of a Centipede estimated to have had 21 or 23 segments; the length of the preserved portion of the body is 17.7 mm. 

Scolopendromorph Chilopod Permocryptops shelleyi, from the Isady locality, upper Permian of Russia. (A), (D) General view of part and counterpart (mirror-reversed), respectively. (B) Drawing compiled from part and counterpart. (C. Ultimate legs. (E) Pore ields and ventrodistal spines on the ultimate coxae. Abbreviations: po fi; pore field, sp, coxal spine; numbers in parentheses are segment numbers assuming 23 segments are present. Khramov et al. (2018).

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