Fossils not only provide unique opportunity to understand the "tempo and mode" of evolution but are essential for modeling lineage-contingent diversification histories. Here, we interrogate the Mesozoic fossil record of the Aculeata, with emphasis on the ants (Formicidae), and conduct an extended series of ancestral state estimation exercises on distributions of tip-dated combined-evidence phylogenies. We developed and illustrated from ground-up a set of 576 morphological characters which we scored for 144 extant and 431 fossil taxa; we used average posterior probability support to filter this to a target matrix of 303 taxa, for which we integrated strongly filtered ultraconserved element (UCE) data for 115 living species. We also implemented reversible jump MCMC (rjMCMC) and hidden state methods to model complex behavioral characters to test hypotheses about the pathway to obligate eusociality. In addition to revising the higher classification of all sampled groups to family or subfamily level using estimated character polarities to diagnose nodes across the phylogeny, we find that the mid-Cretaceous genera †Camelomecia and †Camelosphecia form a clade which is robustly supported as sister to the total clade Formicidae. For this reason, we name this extinct clade as †@@@idae fam. nov. and provide a definition for the expanded Formicoidea. Based on our results, we recognize three major phases in the early evolution of the ants: (1) origin of ants as running-adapted huntresses during the Late Jurassic in the "stinging aggressor" guild (Aculeata) among various lineages of "sneaking parasitoids" (non-aculeate Vespina); (2) the first formicoid radiation during the Early Cretaceous, by the end of which all major extant ant linages had originated; and (3) turnover of the Formicoidea at the end-Cretaceous leading to the second formicoid radiation, i.e., the Cenozoic formicid diversification. We conclude with a concentrated series of considerations for future directions of study with this dataset and beyond.

Although molecular data have proven indispensable in confidently resolving the phylogeny of many clades across the tree of life, these data may be inaccessible for certain taxa. The resolution of taxonomy in the ant subfamily Leptanillinae is made problematic by the absence of DNA sequence data for leptanilline taxa that are known only from male specimens, including the monotypic genus Phaulomyrma Wheeler & Wheeler. Focusing upon the considerable diversity of undescribed male leptanilline morphospecies, the phylogeny of 35 putative morphospecies sampled from across the Leptanillinae, plus an outgroup, is inferred from 11 nuclear loci and 41 discrete male morphological characters using a Bayesian total-evidence framework, with Phaulomyrma represented by morphological data only. Based upon the results of this analysis Phaulomyrma is synonymised with Leptanilla Emery, and male-based diagnoses for Leptanilla that are grounded in phylogeny are provided, under both broad and narrow circumscriptions of that genus. This demonstrates the potential utility of a total-evidence approach in inferring the phylogeny of rare extant taxa for which molecular data are unavailable and begins a long-overdue systematic revision of the Leptanillinae that is focused on male material.

Subterranean termites in the genus Heterotermes Froggatt (Rhinotermitidae: Heterotermitinae) are pantropical wood feeders capable of causing significant structural damage. The aim of this study was to investigate soldier morphological attributes in three Puerto Rican species of Heterotermes previously identified by sequencing of two mitochondrial genes and attributed to Heterotermes tenuis (Hagen), H. convexinotatus (Snyder) and H. cardini (Snyder). Soldiers (n = 156) were imaged and measured using the Auto-Montage image-stacking program. We demonstrated that Puerto Rican Heterotermes soldiers could not be identified to species level based upon seven morphometric indices or any combination thereof. Nor could differences in soldier head pilosity be used to discriminate species, in contrast to previous findings. However, previously described characters of the soldier tergal setae were reported to be useful in discriminating H. tenuis from both of its Puerto Rican congeners.

The ant subfamily Leptanillinae (Hymenoptera: Formicidae) consists of minute soil-dwelling species, with several genera within this clade being based solely upon males, including Yavnella Kugler. The dissociation of males and workers has resulted in taxonomic confusion for the Leptanillinae. We here describe the worker caste of Yavnella, facilitated by maximum-likelihood and Bayesian inference from 473 partitioned ultra-conserved element loci, this dataset including 49 other leptanilline species, both described and undescribed. Yavnella laventa sp. nov. is described from seven worker specimens collected in south-western Iran from the Milieu Souterrain Superficiel, a subterranean microhabitat consisting of air-filled cavities among rock and soil fragments, which is subject to similar environmental conditions as caves. This species has bizarrely elongated appendages, which suggests that it is confined to cavities, in contrast with the soil-dwelling behaviour observed in other leptanilline ants. Based on its gracile phenotype relative to other Leptanillinae, Y. laventa shows remarkable adaptations for subterranean life, making it one of a very few examples of this syndrome among the ants. Moreover, the discovery of the worker caste of Yavnella expands our morphological knowledge of the leptanilline ants. We provide worker-and male-based diagnoses of Yavnella, along with a key to the genera of the Leptanillinae for which workers are known. The worker caste of Yavnella as known from this species is immediately recognisable, but the possibility must be noted that described workers of Leptanilla may in fact belong to Yavnella. Further molecular sampling is required to test this hypothesis.