The fossil history of pseudoscorpions (Arachnida: Pseudoscorpiones)

Abstract

Abstract. Pseudoscorpions, given their resemblance to scorpions, have attracted human attention since the time of Aristotle, although they are much smaller and lack the sting and elongated tail. These arachnids have a long evolutionary history but their origins and phylogenetic affinities are still being debated. Here, we summarise their fossil record based on a comprehensive review of the literature and data contained in other sources. Pseudoscorpions are one of the oldest colonisers of the land, with fossils known since the Middle Devonian (ca. 390 Ma). The only arachnid orders with an older fossil record are scorpions, harvestmen and acariform mites, plus two extinct groups. Pseudoscorpions do not fossilise easily, and records from the Mesozoic and Cenozoic consist almost exclusively of amber inclusions. Most Mesozoic fossils come from Archingeay and Burmese ambers (Late Cretaceous) and those from the Cenozoic are primarily from Eocene Baltic amber, although additional fossils from, for example, Miocene Dominican and Mexican ambers, are known. Overall, 16 of the 26 families of living pseudoscorpions have been documented from fossils and 49 currently valid species are recognised in the literature. Pseudoscorpions represent a case of morphological stasis and even the Devonian fossils look rather modern. Indeed, most amber fossils are comparable to Recent groups despite a major gap in the fossil record of almost 250 Myr. Baltic amber inclusions indicate palaeofauna inhabiting much warmer climates than today and point to climatic shifts in central Europe since the Eocene. They also indicate that some groups (e.g. Feaellidae and Pseudogarypidae) had much wider Eocene distributions. Their present-day occurrence is relictual and highlights past extinction events. Faunas from younger tropical amber deposits (e.g. Dominican and Mexican amber) are comparable to Recent ones. Generally, there is a strong bias in the amber record towards groups that live under tree bark, whereas those from litter habitats are underrepresented. We also discuss challenges in interpreting fossils: their cryptic morphology warranting novel techniques of morphological reconstruction, the massive gap in the fossil record between the Palaeozoic and Mesozoic, and problems with the classification of (historically) old amber material. Finally, we discuss aspects of the palaeoecology and biology of the fossils compared with the Recent fauna, such as phoresy.

Transcriptomic Analysis of Pseudoscorpion Venom Reveals a Unique Cocktail Dominated by Enzymes and Protease Inhibitors

“…These animals live in almost all terrestrial habitats, commonly in leaf litter or soil, but also in caves or littoral habitats [ 2 ]. Like many arachnid orders, pseudoscorpions appeared in the fossil record of the Devonian, with the oldest crown group fossils dating back to 390 Ma [ 3 ]. Their phylogenetic position remains controversial.…”

Unravelling the mystery of “Madagascar copal”: Age, origin and preservation of a Recent resin

“…The lack of dating of the pieces of "Madagascar copal", including their bioinclusions, is a recurrent but never discussed topic in taxonomic publications. This predicament triggers problems in other research fields such as biogeography [139,140,141], phylogeny [142,143] or molecular clocks [144].…”

Arachnids in Bitterfeld amber: A unique fauna of fossils from the heart of Europe or simply old friends?

“…Pseudoscorpions in Bitterfeld amber are likely to represent a diverse fauna which, to date, remains largely undocumented. The fossil history of pseudoscorpions was recently reviewed by Harms and Dunlop (2017) and a total of 49 fossil species in 16 families are currently recognised, of which the majority (34 species in 12 families) were described from Baltic amber. Our preliminary assessment of the Bitterfeld pseudoscorpions suggests that at least nine families are present: Chthoniidae, Tridenchthoniidae, Pseudogarypidae, Neobisiidae, Geogarypidae, Cheiridiidae, Chernetidae, Cheliferidae, and Withiiidae.…”

“…The pseudoscorpion and mite faunas lie essentially bare. While not much can be said about the mites at present, other than that they are abundant with several hundred specimens, the lack of any pseudoscorpion descriptions from Bitterfeld is notable because the Baltic amber pseudoscorpion fauna is very well documented (Harms and Dunlop 2017) and yields about two-thirds of the global fossil diversity for this taxon. As with other arthropod groups, there seem to be some shared morphospecies, but also a number of unique taxa in the chthoniid and neobisiid fauna which may support the hypothesis of a partly distinct status for Bitterfeld versus Baltic amber; irrespective of whether this reflects geographical or temporal differences.…”