Fossil Record 20(2): 215-238, doi: 10.5194/fr-20-215-2017
The fossil history of pseudoscorpions (Arachnida: Pseudoscorpiones)
expand article infoDanilo Harms, Jason A. Dunlop§
‡ Zoological Museum, Center of Natural History, University of Hamburg, Hamburg, Germany§ Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany
Open Access
Pseudoscorpions, given their resemblance to scorpions, have attracted human attention sincethe time of Aristotle, although they are much smaller and lackthe sting and elongated tail. These arachnids have a long evolutionaryhistory but their origins and phylogenetic affinities are still beingdebated. Here, we summarise their fossil record based on a comprehensivereview of the literature and data contained in other sources. Pseudoscorpionsare one of the oldest colonisers of the land, with fossils known since theMiddle Devonian (ca. 390 Ma). The only arachnid orders with an olderfossil record are scorpions, harvestmen and acariform mites, plus two extinctgroups. Pseudoscorpions do not fossilise easily, and records from theMesozoic and Cenozoic consist almost exclusively of amber inclusions. MostMesozoic fossils come from Archingeay and Burmese ambers (Late Cretaceous)and those from the Cenozoic are primarily from Eocene Baltic amber, althoughadditional fossils from, for example, Miocene Dominican and Mexicanambers, are known. Overall, 16 of the 26 families of living pseudoscorpions have beendocumented from fossils and 49 currently valid species are recognised in theliterature. Pseudoscorpions represent a case of morphological stasis and eventhe Devonian fossils look rather modern. Indeed, most amber fossils arecomparable to Recent groups despite a major gap in the fossil record ofalmost 250 Myr. Baltic amber inclusions indicate palaeofauna inhabitingmuch warmer climates than today and point to climatic shifts in centralEurope since the Eocene. They also indicate that some groups (e.g. Feaellidaeand Pseudogarypidae) had much wider Eocene distributions. Theirpresent-day occurrence is relictual and highlights past extinctionevents. Faunas from younger tropical amber deposits (e.g. Dominican and Mexicanamber) are comparable to Recent ones. Generally, there is a strong bias inthe amber record towards groups that live under tree bark, whereas those fromlitter habitats are underrepresented. We also discuss challenges ininterpreting fossils: their cryptic morphology warranting novel techniques ofmorphological reconstruction, the massive gap in the fossil record betweenthe Palaeozoic and Mesozoic, and problems with the classification of(historically) old amber material. Finally, we discuss aspects of thepalaeoecology and biology of the fossils compared with the Recent fauna, suchas phoresy.