The Eumetabola (Endopterygota (also known as Holometabola) plus Paraneoptera)1 have the highest number of species of any clade, and greatly contribute to animal species biodiversity2,3. The palaeoecological circumstances that favoured their emergence and success remain an intriguing question3,4,5,6. Recent molecular phylogenetic analyses have suggested a wide range of dates for the initial appearance of the Holometabola, from the Middle Devonian epoch (391 million years (Myr) ago) to the Late Pennsylvanian epoch (311 Myr ago7,8,9,10,11,12), and Hemiptera (310 Myr ago13). Palaeoenvironments greatly changed over these periods, with global cooling and increasing complexity of green forests14. The Pennsylvanian-period crown-eumetabolan fossil record remains notably incomplete15,16,17,18,19, particularly as several fossils have been erroneously considered to be stem Holometabola1,15,20,21 (Supplementary Information); the earliest definitive beetles are from the start of the Permian period21,22. The emergence of the hymenopterids, sister group to other Holometabola, is dated between 350 and 309 Myr ago8,9,12, incongruent with their current earliest record (Middle Triassic epoch)1,20. Here we describe five fossils— a Gzhelian-age stem coleopterid, a holometabolous larva of uncertain ordinal affinity, a stem hymenopterid, and early Hemiptera and Psocodea, all from the Moscovian age—and reveal a notable penecontemporaneous breadth of early eumetabolan insects. These discoveries are more congruent with current hypotheses of clade divergence. Eumetabola experienced episodes of diversification during the Bashkirian–Moscovian and the Kasimovian–Gzhelian ages. This cladogenetic activity is perhaps related to notable episodes of drying resulting from glaciations, leading to the eventual demise in Euramerica of coal-swamp ecosystems, evidenced by floral turnover during this interval23,24. These ancient species were of very small size, living in the shadow of Palaeozoic-era ‘giant’ insects. Although these discoveries reveal unexpected Pennsylvanian eumetabolan diversity, the lineage radiated more successfully only after the mass extinctions at the end of the Permian period, giving rise to the familiar crown groups of their respective clades.
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We thank C. C. Labandeira for comments on the first version of the manuscript that helped to improve the paper. We are grateful to A. P. Rasnitsyn, S. I. Golovach and B. R. Striganova, M. Fikáček, A.A. Przhiboro, R. Beutel, T. Hörnschemeyer and V. Krassilov for early discussions. C. Garrouste and P. A. Kirejtshuk assisted in the preparation of illustrations for this publication. Financial support was provided by the Grant Agency of the Czech Republic no. P210/10/0633 (to J.P.) and the German Science Foundation WA 1492/6-1 (to T.W.). The study was supported by the program for visiting researchers and professors of the Smithsonian Institution National Museum of Natural History (NMNH) and partly carried out within the framework of the program of the Presidium of the Russian Academy of Sciences ‘Problems of the origin of life and formation of the biosphere’. A.A.P. and A.G.K. were supported by the Russian Foundation of Basic Research (grant 12-04-00663-a). This paper is a participation to the team project ‘Biodiversity: Origin, Structure, Evolution and Geology’ allotted to D.A. by the Lebanese University.
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