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Butterflies are a diverse and charismatic insect group that are thought to have evolved with plants and dispersed throughout the world in response to key geological events. However, these hypotheses have not been extensively tested because a comprehensive phylogenetic framework and datasets for butterfly larval hosts and global distributions are lacking. We sequenced 391 genes from nearly 2,300 butterfly species, sampled from 90 countries and 28 specimen collections, to reconstruct a new phylogenomic tree of butterflies representing 92% of all genera. Our phylogeny has strong support for nearly all nodes and demonstrates that at least 36 butterfly tribes require reclassification. Divergence time analyses imply an origin ~100 million years ago for butterflies and indicate that all but one family were present before the K/Pg extinction event. We aggregated larval host datasets and global distribution records and found that butterflies are likely to have first fed on Fabaceae and originated in what is now the Americas. Soon after the Cretaceous Thermal Maximum, butterflies crossed Beringia and diversified in the Palaeotropics. Our results also reveal that most butterfly species are specialists that feed on only one larval host plant family. However, generalist butterflies that consume two or more plant families usually feed on closely related plants., Funding came from the US National Science Foundation (NSF) GoLife ‘ButterflyNet’ collaborative grant (DEB-1541500, 1541557, 1541560) to A.Y.K., R.P.G., D.J.L. and N.E.P. Specimen collection and preservation was funded by NSF DBI-1349345, 1601369, DEB-1557007 and IOS-1920895 (A.Y.K.), NSF DEB-1120380 (D.J.L.), grants 9285-13 and WW-227R-17 from the National Geographic Society (D.J.L.), NSF DBI-1256742 (A.Y.K. and K.R.W.), NSF DEB-0639861 (K.R.W.) and NSF SES-0750480, DEB-0447244 and DEB-9615760 (N.E.P.). M.E. was supported by the Research Council of Norway (no. 204308) and the Hintelmann Scientific Award for Zoological Systematics. F.L.C. was supported by the European Research Council under the European Union’s Horizon 2020 research and innovation programme (project GAIA, no. 851188). M.P.B. was supported by the Swedish Research Council (IPG no. 2020‐06422). R.V. was supported by the Spanish Ministry of Science and Innovation grant PID2019-107078GB-I00/AEI/10.13039/501100011033. G.T. was supported by the Spanish Ministry of Science and Innovation (grants PID2020-117739GA-I00/AEI/10.13039/501100011033 and RYC2018-025335-I). V.L. was supported by the Russian Science Foundation (grant 19-14-00202) and by the Ministry of Science and Higher Education of the Russian Federation (grant 075-15-2021-1069). M.Y. was supported by MEXT KAKENHI no. 19916010 and JSPS KAKENHI grants 13010131, 23570111, 26440207, 17K07528 and 21H02215. A.B.B.M., H.P.R. and N.O.M. were supported by CNPQ grants proc 563332/2010-7 and 304273/2014-7., Main Results and discussion Methods Data availability Code availability References Acknowledgements Author information Ethics declarations Peer review Additional information Supplementary information Rights and permissions About this article

Butterflies are a diverse and charismatic insect group that are thought to have diversified via coevolution with plants and in response to dispersals following key geological events. These hypotheses have been poorly tested at the macroevolutionary scale because a comprehensive phylogenetic framework and datasets on global distributions and larval hosts of butterflies are lacking. We sequenced 391 genes from nearly 2,000 butterfly species to construct a new, phylogenomic tree of butterflies representing 92% of all genera and aggregated global distribution records and larval host datasets. We found that butterflies likely originated in what is now the Americas, ∼100 Ma, shortly before the Cretaceous Thermal Maximum, then crossed Beringia and diversified in the Paleotropics. The ancestor of modern butterflies likely fed on Fabaceae, and most extant families were present before the K/Pg extinction. The majority of butterfly dispersals occurred from the tropics (especially the Neotropics) to temperate zones, largely supporting a “cradle” pattern of diversification. Surprisingly, host breadth changes and shifts to novel host plants had only modest impacts.