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Abstract The classification of ants (Hymenoptera: Formicidae) has progressed in waves since the first 17 species were described by Linnaeus in the 1758 edition of Systema Naturae. Since then, over 18,000 species-rank names have accumulated for the global myrmecofauna, of which ~14,260 living and ~810 fossil species are valid. Here, we provide a synopsis of ant biodiversity and review the history and classification of the family, while highlighting the massive growth of the field in the new millennium. We observe that major transformation has occurred for ant classification due to advances in DNA sequencing technologies, model-based hypothesis testing, and imaging technologies. We therefore provide a revised and illustrated list of diagnostic character states for the higher clades of Formicidae, recognizing that vastly more work is to be done. To facilitate discussion and the systematic accumulation of evolutionary knowledge for the early evolution of the ants, we suggest an informal nomenclatural system for the higher clades of ants, based on names currently in use and a set of names that have been democratically selected by the authors. To guide future work on ant systematics, we summarize currently available databases and present perspectives on regions in need of biodiversity exploration, challenges facing the field, and the future of ant taxonomy. 

Abstract Dorymyrmex Mayr 1866, the ‘pyramid ants’ or ‘cone ants’, are conspicuous inhabitants of arid landscapes across the Americas. Ranging from the Great Plains to Patagonia, they are concentrated north and south of the tropics in contrast to the latitudinal diversity gradient canon. Despite being frequently collected and ecologically important, Dorymyrmex ants exemplify the taxonomic neglect typical in the subfamily Dolichoderinae. The genus has never had the benefit of a global revision, and even the major lineages are still uncertain. This work characterizes the issues at hand and ushers 22 Dorymyrmex species into the world of modern-day phylogenomics: By targeting ultraconserved elements (UCEs) across the genome, I construct an alignment of 1,891 loci, infer phylogenies under maximum likelihood and Bayesian approaches, and estimate divergence dates. Three major clades of Dorymyrmex emerge with maximal support, corresponding to former genera: Dorymyrmex sensu stricto, Araucomyrmex Gallardo 1919, and Conomyrma Forel 1913. The pyramicus group (‘Conomyrma’) shows a recent, rapid radiation with minimal morphological differentiation, reaffirming the difficulty of species delimitation in this widespread clade. Finally, I observe a general south-to-north pattern of dispersal, likely by way of savanna ‘stepping stones’ across the tropics during cooler, drier periods. Intercontinental dispersal occurred after the hypothetical Caribbean landspan in the Miocene, but before the Pleistocene or the completion of the Panamanian isthmus, suggesting dispersal by flight. This corroborates patterns observed in other arid-adapted amphitropical New World taxa. Characterizing the major Dorymyrmex species groups is an important first step towards stable taxonomic definitions—which underpin active studies in behavior, chemical ecology, and physiology.