The oldest chthonioid pseudoscorpion Arachnida: Pseudoscorpiones: Chthonioidea: Chthoniidae: A new genus and species from mid-Cretaceous Burmese amber

Pseudoscorpions are an ancient lineage of arachnids but have a scarce fossil record, presumably because these animals are small (2-8 mm in body length) and live in habitats where they do not fossilize easily. This is particularly the case for one of the more basal lineages, the superfamily Chthonioidea, which are common and diverse in leaf litter habitats across the world but have only been described in the fossil record from some specimens in Baltic, Dominican and Chiapas ambers. Here, we describe and illustrate the oldest pseudoscorpion of the superfamily Chthonioidea from the mid-Cretaceous (lowermost Cenomanian, ca. 99 Mya) amber of northern Myanmar and extend the known fossil record of this diverse superfamily from the Eocene into the Cretaceous. Fragments that suggest a diverse pseudoscorpion fauna have been recorded in Myanmar (Burmese) amber but this is only the fourth pseudoscorpion fossil described from this ancient amber type. The single adult female specimen is substantially older than the next oldest fossil chthonioids, which were described from Baltic amber (ca. 44-49 Mya), and displays small but significant differences to other chthonioids, such that we describe a new genus and species, Weygoldtiella plausus gen. et sp. nov. The placement of the trichobothria on the chelal hand suggests it can be attributed to the family Chthoniidae, but important morphological features are obscured in the fossil which obfuscates hypotheses regarding its nearest relatives. The specimen, although imperfectly preserved, has no known Recent relatives in this area or elsewhere in the diverse chthonioid fauna, and may represent an extinct lineage. Overall, this fossil is another example of the diverse arachnid community preserved in Burmese amber that includes lineages that are now extinct here and of considerable biogeographic interest, e.g. ricinuleids, and fauna which is essentially modern, e.g. solifuges.