Emergence of a superradiation: pselaphine rove beetles in mid-Cretaceous amber from Myanmar and their evolutionary implications

Abstract

Pselaphinae is an exceptionally species-rich, globally distributed subfamily of minute rove beetles (Staphylinidae), many of which are inquilines of social insects. Deducing the factors that drove pselaphine diversification and their evolutionary predisposition to inquilinism requires a reliable timescale of pselaphine cladogenesis. Pselaphinae is split into a small and highly plesiomorphic supertribe, Faronitae, and its sister group, the 'higher Pselaphinae' – a vast multi-tribe clade with a more derived morphological ground plan, and which includes all known instances of inquilinism. The higher Pselaphinae is dominated by tribes with a Gondwanan taxonomic bias. However, a minority of tribes are limited to the Nearctic and Palearctic ecozones, implying a potentially older, Pangaean origin of the higher Pselaphinae as a whole. Here, I describe fossils from mid-Cretaceous (∼99 million years old) Burmese amber that confirm the existence of crown-group higher pselaphines on the Eurasian supercontinent prior to contact with Gondwanan landmasses. Protrichonyx rafifrons gen. et sp.n. is placed incertae sedis within the higher Pselaphinae. Boreotethys gen.n., erected for B. grimaldii sp.n. and B. arctopteryx sp.n., represents an extinct sister taxon and putative stem group of Bythinini, a Recent tribe with a primarily Holarctic distribution. The Laurasian palaeolocality of the newly described taxa implies that higher pselaphines are indeed probably of Jurassic, Pangaean extraction and that the Laurasian-Gondwanan tribal dichotomy of this clade may have developed vicariantly following Pangaean rifting. Higher pselaphines probably predate the earliest ants. Their physically protective morphological ground plan may have been a preadaptation for myrmecophily when ants became diverse and ecologically ubiquitous, much later in the Cenozoic.

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