Understanding the link between ecology and morphology is a fundamental goal in biology. Ants are diverse terrestrial organisms, known to exhibit ecologically driven morphological variation. While relationships between individual traits and ecologies have been identified, multidimensional interactions among traits and their cumulative predictive power remain unknown. As selective pressures may generate convergent syndromes spanning multiple traits, we applied multivariate analyses across a wide sampling of taxa to assess ecomorphological variation in an integrative context. How well does morphology predict ecology? Moreover, are there quantitatively supported ant ecomorphs? We investigated the links between trait morphology and ecology by assembling a morphometric dataset spanning over 160 species within 110 genera. As ants occupy a wide range of ecologies, we compiled natural history data on nesting microhabitat, foraging stratum and functional role into 35 defined niche combinations. This tripartite ecological classification and our morphological dataset were optimized under dimension reduction techniques including principal component analysis, principal coordinate analysis, linear discriminant analysis and random forest supervised machine learning. Our results describe ant ecomorphospace as comprising regions of shared, generalized morphology as well as unique phenotypic space associated with specialized ecologies. Dimension reduction and model‐based approaches predict ecology with 77%–85% accuracy and Random Forest analysis consistently outperforms LDA. While accounting for shared ancestry, we found eye, antennal scape and leg morphology to be most informative in differentiating among ecologies. We also note some heterogeneity between trait significance in each ecological aspect (nesting niche, foraging niche, functional role). To increase the utility of ecomorphological classification we simplified our 35 observed niche combinations into 10 ecomorph syndromes, which were also predicted by morphology. The predictive power of these machine learning methods underscores the strong role that ecology has in convergently shaping overall body plan morphology across ant lineages. We include a pipeline for predictive ecomorphological modelling using morphometric data, which may be expanded with additional specimen‐based and natural history data. A free Plain Language Summary can be found within the Supporting Information of this article.

Among social insects, army ants are exceptional in their voracious coordinated predation, nomadic life history and highly specialized wingless queens: the synthesis of these remarkable traits is referred to as the army ant syndrome. Despite molecular evidence that the army ant syndrome evolved twice during the mid-Cenozoic, once in the Neotropics and once in the Afrotropics, fossil army ants are markedly scarce, comprising a single known species from the Caribbean 16 Ma. Here we report the oldest army ant fossil and the first from the Eastern Hemisphere (EH), Dissimulodorylus perseus , preserved in Baltic amber dated to the Eocene. Using a combined morphological and molecular ultra conserved elements dataset spanning doryline lineages, we find that D. perseus is nested among extant EH army ants with affinities to Dorylus. Army ants are characterized by limited extant diversification throughout most of the Cenozoic; the discovery of D. perseus suggests an unexpected diversity of now-extinct army ant lineages in the Cenozoic, some of which were present in Continental Europe.

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Fossilized plant resins, or ambers, offer a unique paleontological window into the history of life. A natural polymer, amber can preserve aspects of ancient environments, including whole organisms, for tens or even hundreds of millions of years. While most amber research involves imaging with visual light, other spectra are increasingly used to characterize both organismal inclusions as well as amber matrix. Terahertz (THz) radiation, which occupies the electromagnetic band between microwave and infrared light wavelengths, is non-ionizing and frequently used in polymer spectroscopy. Here, we evaluate the utility of amber terahertz spectroscopy in a comparative setting for the first time by analyzing the terahertz optical properties of samples from 10 fossil deposits ranging in age from the Miocene to the Early Cretaceous. We recover no clear relationships between amber age or botanical source and terahertz permittivity; however, we do find apparent deposit-specific permittivity among transparent amber samples. By comparing the suitability of multiple permittivity models across sample data we find that models with a distribution of dielectric relaxation times best describe the spectral permittivity of amber. We also demonstrate a process for imaging amber inclusions using terahertz transmission and find that terahertz spectroscopy can be used to identify some synthetic amber forgeries.

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