A new stem bythinine in Cretaceous Burmese amber and early evolution of specialized predatory behaviour in pselaphine rove beetles (Coleoptera: Staphylinidae)

Abstract

Comprising more than 10,000 valid species, the staphylinid subfamily Pselaphinae is a major element of epigean habitats, and among the most diverse groups of rove beetles. Pselaphinae is split basally into two principal clades: the small supertribe Faronitae, and its sister group, the hyper-diverse 'higher Pselaphinae' containing the remaining five supertribes. Deducing the origins and divergence times of major higher Pselaphinae clades requires direct fossil evidence. Here we describe a new pselaphine rove beetle, Cretobythus excavatus Yin, Parker & Cai gen. et sp. nov., based on a well-preserved individual embedded in mid-Cretaceous amber from Myanmar (Cenomanian, c. 99 Ma). Cretobythus does not obviously belong to any Recent tribe, but Bayesian phylogenetic placement using morphological characters supports a position within the stem-group of the tribe Bythinini, sister to Boreotethys Parker, a genus also recently described from Burmese amber. Together, Cretobythus + Boreotethys comprise the sister group of modern Bythinini. Despite some external similarities to Recent Bythinini, Cretobythus exhibits several plesiomorphic traits, including a generally flattened body plan, and metacoxae that are positioned close to the ventral midline. The resemblance in form of the enlarged maxillary palpi of Cretobythus to extant bythinines implies a similar function in prey capture, indicating that the unusual employment of the maxillary palps to trap moving prey in Bythinini had probably evolved by the mid-Cretaceous, at the latest.

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