The evolutionary history of body organisation in the lineage towards modern scorpions


Authors: Haug C, Wagner P, Haug JT

Published in: Bulletin of Geosciences, volume 94, issue 4; pages: 389 - 408; Received 21 February 2019; Accepted in revised form 21 October 2019; Online 10 December 2019

Keywords: tagmosis, tagmatization, feeding apparatus, character polarisation, pectines, book lungs,

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The enormous evolutionary success of euarthropods (insects, crustaceans, myriapods, chelicerates, and their relatives) is generally thought to be coupled to their specific mode of body organisation, also called tagmosis. Their body segments are organised into groups of segments, which share specific functions; these functional units are called tagmata. The patterns of tagmosis differ between the different euarthropod groups, and some of these patterns appear to be constant since the earliest appearance of the group. However, often no strict criteria have been applied which characterise a tagma as such. We provide here a new view on the tagmosis of scorpions and the evolutionary history behind it, by applying criteria already successfully used for elucidating the tagmosis of other euarthropods. Our study shows that the tagmosis changed several times from the ground pattern of Euarthropoda to modern scorpions, the latter ones possessing a tagmosis not present in the earliest scorpions. This difference mainly concerns the region of the sternum, the genital operculum and the pectines. We provide additional data which cast doubt on the presence of pectines in early scorpions. Our argumentation provides an explanation for the evolution of tagmosis in modern scorpions with less conflict than hypotheses proposed earlier.


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