The smallest stag beetles (Coleoptera, Lucanidae): hidden paleodiversity in mid-Cretaceous Kachin amber from northern Myanmar

The fossil record of stag beetles (Lucanidae), especially in Mesozoic amber, is sparse. Four additional fossil lucanids preserved in mid-Cretaceous Kachin amber from northern Myanmar are here reported. All of these species are included in the primitive subfamily Aesalinae, and have been identified as: Protonicagus mandibularis sp. nov. (tribe Nicagini); Cretognathus minutissimus gen. et sp. nov. (tribe Ceratognathini); Ceratognathini gen. et sp. indet. 1 (provisional assignment); and Ceratognathini gen. et sp. indet. 2 (provisional assignment). Except for Protonicagus mandibularis sp. nov., the stag beetles appear to be connected to the continent of Gondwana, as with the Kachin amber paleofauna. More interestingly, these species have significantly smaller bodies than the extant species, with three of them measuring less than 3 mm, which makes them the smallest known species of Lucanidae. This finding is congruent with a trend toward miniaturization in several unrelated lineages of Kachin amber beetles, and it shows hidden paleodiversity of stag beetles during the Cretaceous

Evidence for social parasitism of early insect societies by Cretaceous rove beetles

The evolution of eusociality in ants and termites propelled both insect groups to their modern ecological dominance. Yet, eusociality also fostered the evolution of social parasitism—an adverse symbiosis, in which the superorganismal colonies formed by these insects are infiltrated by a profusion of invertebrate species that target nest resources. Predominant among these are the aleocharine rove beetles (Staphylinidae), a vast and ecologically diverse subfamily with numerous morphologically and behaviourally specialized socially parasitic lineages. Here, we report a fossil aleocharine, Mesosymbion compactus gen. et sp. nov., in Burmese amber (∼99 million years old), displaying specialized anatomy that is a hallmark of social parasites. Mesosymbion coexisted in the Burmese palaeofauna with stem-group ants and termites that provide the earliest indications of eusociality in both insect groups. We infer that the advent of eusociality led automatically and unavoidably to selection for social parasitism. The antiquity and adaptive flexibility of aleocharines made them among the first organisms to engage in this type of symbiosis

Cretaceous origin of the unique prey-capture apparatus in mega-diverse genus:stem lineage of Steninae rove beetles discovered in Burmese amber

Stenus is the largest genus of rove beetles and the second largest among animals. Its evolutionary success was associated with the adhesive labial prey-capture apparatus, a unique apomorphy of that genus. Definite Stenus with prey-capture apparatus are known from the Cenozoic fossils, while the age and early evolution of Steninae was hardly ever hypothesized. Our study of several Cretaceous Burmese amber inclusions revealed a stem lineage of Steninae that possibly possesses the Stenus-like prey-capture apparatus. Phylogenetic analysis of extinct and extant taxa of Steninae and putatively allied subfamilies of Staphylinidae with parsimony and Bayesian approaches resolved the Burmese amber lineage as a member of Steninae. It justified the description of a new extinct stenine genus Festenus with two new species, F. robustus and F. gracilis. The Late Cretaceous age of Festenus suggests an early origin of prey-capture apparatus in Steninae that, perhaps, drove the evolution towards the crown Stenus. Our analysis confirmed the well-established sister relationships between Steninae and Euaesthetinae and resolved Scydmaeninae as their next closest relative, the latter having no stable position in recent phylogenetic studies of rove beetles. Close affiliation of Megalopsidiinae, a subfamily often considered as a sister group to Euaesthetinae + Steninae clade, is rejected

New species of Paraodontomma from mid-Cretaceous Burmese amber with muscle tissue preservation (Coleoptera: Archostemata: Ommatidae)

The third member of the extinct ommatid genus Paraodontomma is reported from mid-Cretaceous Burmese amber. Our observation confirms the transverse ridges on elytra as a diagnostic character for the genus. Paraodontomma leptocristatum sp. nov. differs from previously reported congeners mainly in head subquadrate and without prominent protuberances, pronotal disc without prominent ridges, elytral ridges indistinct, and teeth along elytral margins not forming a wavy pattern. Musculature is preserved in the newly discovered specimen of P. leptocristatum, which further demonstrates the preservation potential and irreplaceable value of amber fossils

First fossil species of ship-timber beetles (Coleoptera, Lymexylidae) from Eocene Rovno amber (Ukraine)

A new lymexylid fossil species, †Raractocetus sverlilo Nazarenko, Perkovsky & Yamamoto, sp. nov., is described from late Eocene Rovno amber of Ukraine. This new species is similar to species of the recent genera Atractocerus Palisot de Beauvois and Raractocetus Kurosawa in the ship-timber beetle subfamily Atractocerinae, but differs in pronotal and elytral features. Notably, the new species is one of the smallest atractocerines known to date. This is the first member of the family Lymexylidae found in Rovno amber. Our finding sheds further light on the paleodiversity of atractocerine beetles, highlighting a peculiar distribution during the Eocene. Only one extant atractocerine specimen has been reported from Europe (Greece), while three species from Eocene European amber forests with equable climate are known now, including two species from the otherwise tropical genus Raractocetus. Our finding of the Raractocetus beetle from Rovno amber is of significant biogeographically because it indicates the wide distribution of the genus in the Eocene European amber forests

Evidence for the evolution of eusociality in stem ants and a systematic revision of †Gerontoformica (Hymenoptera: Formicidae)

It is generally assumed that Cretaceous stem ants were obligately eusocial, because of the presence of wingless adult females, yet the available evidence is ambiguous. Here, we report the syninclusion of a pupa and adult of a stem ant species from Mid-Cretaceous amber. As brood are immobile, the pupa was likely to have been transported by an adult. Therefore, the fossil substantiates the hypothesis that wingless females were cooperators, thus these were true ‘workers’. Re-examination of all described Cretaceous ant species reveals that winged–wingless diphenism – hence a variable dispersal capacity – may have been ancestral to the total clade of the ants, and that highly specialized worker-specific phenotypes evolved in parallel between the stem and crown groups. The soft-tissue preservation of the fossil is exceptional, demonstrating the possibility of analysing the development of the internal anatomy in stem ants. Based on the highest-resolution µ-CT scans of stem ants to date, we describe †Gerontoformica sternorhabda sp. nov., redescribe †G. gracilis, redefine the species group classification of †Gerontoformica, and provide a key to the species of the genus. Our work clarifies the species boundaries of †Gerontoformica and renders fossils relevant to the discussion of eusocial evolution in a way that has heretofore been intractable.journal articl

Integrated phylogenomics and fossil data illuminate the evolution of beetles

Beetles constitute the most biodiverse animal order with over 380,000 described species and possibly several million more yet unnamed. Recent phylogenomic studies have arrived at considerably incongruent topologies and widely varying estimates of divergence dates for major beetle clades. Here we use a dataset of 68 single-copy nuclear protein coding genes sampling 129 out of the 193 recognized extant families as well as the first comprehensive set of fully-justified fossil calibrations to recover a refined timescale of beetle evolution. Using phylogenetic methods that counter the effects of compositional and rate heterogeneity we recover a topology congruent with morphological studies, which we use, combined with other recent phylogenomic studies, to propose several formal changes in the classification of Coleoptera: Scirtiformia and Scirtoidea sensu nov., Clambiformia ser. nov. and Clamboidea sensu nov., Rhinorhipiformia ser. nov., Byrrhoidea sensu nov., Dryopoidea stat. res., Nosodendriformia ser. nov., and Staphyliniformia sensu nov., Erotyloidea stat. nov., Nitiduloidea stat. nov., and Cucujoidea sensu nov., alongside changes below the superfamily level. Our divergence time analyses recovered a late Carboniferous origin of Coleoptera, a late Paleozoic origin of all modern beetle suborders, and a Triassic–Jurassic origin of most extant families, while fundamental divergences within beetle phylogeny did not coincide with the hypothesis of a Cretaceous Terrestrial Revolution

Mesozoic Notocupes revealed as the sister group of Cupedidae (Coleoptera: Archostemata)

Despite encompassing only about 50 extant species, beetles of the suborder Archostemata have a rich fossil history, being known from the Permian and dominating coleopteran assemblages in the Mesozoic before declining in richness towards the Late Cretaceous. Given the limited diversity of extant archostematans, fossils provide a valuable line of evidence for reconstructing the relationships among its constituent families. Here we re-evaluate the phylogenetic position of the Triassic–Cretaceous genus Notocupes, the most species-rich archostematan taxon in the fossil record. Exquisitely preserved fossils from the Middle Jurassic Haifanggou Formation (Daohugou; ~165 Ma) and mid-Cretaceous amber (~99 Ma) reveal critical differences from Ommatidae in the presence of separated procoxae and overlapping abdominal ventrites. Our analyses confirm that Notocupes is not a member of Ommatidae, but is closely related to Cupedidae. Our fossils reveal that Notocupes possessed unique adaptations for protecting their appendages, such as unusual dorsal pronotal grooves for the reception of antennae and epipleural grooves for the reception of legs, shedding light on ecological interactions in Mesozoic saproxylic habitats. The high similarity between Jurassic and Cretaceous Notocupes provides an exceptional example of long-term morphological stasis, suggesting a consistent microhabitat for the group