Prolonged faunal turnover in earliest ants revealed by North American Cretaceous amber.

All ∼14,000 extant ant species descended from the same common ancestor, which lived ∼140-120 million years ago (Ma).1,2 While modern ants began to diversify in the Cretaceous, recent fossil evidence has demonstrated that older lineages concomitantly occupied the same ancient ecosystems.3 These early-diverging ant lineages, or stem ants, left no modern descendants; however, they dominated the fossil record throughout the Cretaceous until their ultimate extinction sometime around the K-Pg boundary. Even as stem ant lineages appear to be diverse and abundant throughout the Cretaceous, the extent of their longevity in the fossil record and circumstances contributing to their extinction remain unknown.3 Here we report the youngest stem ants, preserved in ∼77 Ma Cretaceous amber from North Carolina, which illustrate unexpected morphological stability and lineage persistence in this enigmatic group, rivaling the longevity of contemporary ants. Through phylogenetic reconstruction and morphometric analyses, we find evidence that total taxic turnover in ants was not accompanied by a fundamental morphological shift, in contrast to other analogous stem extinctions such as theropod dinosaurs. While stem taxa showed broad morphological variation, high-density ant morphospace remained relatively constant through the last 100 million years, detailing a parallel, but temporally staggered, evolutionary history of modern and stem ants.

Trait-Based Paleontological Niche Prediction Recovers Extinct Ecological Breadth of the Earliest Specialized Ant Predators.

AbstractPaleoecological estimation is fundamental to the reconstruction of evolutionary and environmental histories. The ant fossil record preserves a range of species in three-dimensional fidelity and chronicles faunal turnover across the Cretaceous and Cenozoic; taxonomically rich and ecologically diverse, ants are an exemplar system to test new methods of paleoecological estimation in evaluating hypotheses. We apply a broad extant ecomorphological dataset to evaluate random forest machine learning classification in predicting the total ecological breadth of extinct and enigmatic hell ants. In contrast to previous hypotheses of extinction-prone arboreality, we find that hell ants were primarily leaf litter or ground-nesting and foraging predators, and by comparing ecospace occupations of hell ants and their extant analogs, we recover a signature of ecomorphological turnover across temporally and phylogenetically distinct lineages on opposing sides of the Cretaceous-Paleogene boundary. This paleoecological predictive framework is applicable across lineages and may provide new avenues for testing hypotheses over deep time.

Deep time extinction of largest insular ant predators and the first fossil Neoponera (Formicidae: Ponerinae) from Miocene age Dominican amber.

BACKGROUND: Ponerine ants are almost exclusively predatory and comprise many of the largest known ant species. Within this clade, the genus Neoponera is among the most conspicuous Neotropical predators. We describe the first fossil member of this lineage: a worker preserved in Miocene-age Dominican amber from Hispaniola. RESULTS: Neoponera vejestoria sp. nov. demonstrates a clear case of local extinction-there are no known extant Neoponera species in the Greater Antilles. The species is attributable to an extant and well-defined species group in the genus, which suggests the group is older than previously estimated. Through CT scan reconstruction and linear morphometrics, we reconstruct the morphospace of extant and fossil ants to evaluate the history and evolution of predatory taxa in this island system. CONCLUSIONS: The fossil attests to a shift in insular ecological community structure since the Miocene. The largest predatory taxa have undergone extinction on the island, but their extant relatives persist throughout the Neotropics. Neoponera vejestoria sp. nov. is larger than all other predatory ant workers known from Hispaniola, extant or extinct. Our results empirically demonstrate the loss of a functional niche associated with body size, which is a trait long hypothesized to be related to extinction risk.

An Eocene army ant.

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.

Non-destructive comparative evaluation of fossil amber using terahertz time-domain spectroscopy.

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.