A formicine in New Jersey Cretaceous amber (Hymenoptera : Formicidae) and early evolution of the ants

A worker ant preserved with microscopic detail has been discovered in Turon ian-aged New Jersey amber [ca. 92 mega-annum (Ma)]. The apex of the gaster has an acidopore and, thus, allows definitive assignment of the fossil to t he large extant subfamily Formicinae, members of which use a defensive spra y of formic acid. This specimen is the only Cretaceous record of the subfam ily, and only two other fossil ants are known from the Cretaceous that uneq uivocally belong to an extant subfamily (Brownimecia and Canapone of the Po nerinae, in New Jersey and Canadian amber, respectively). In lieu of a clad ogram of formicine genera, generalized morphology of this fossil suggests a basal position in the subfamily. Formicinae and Ponerinae in the mid Creta ceous indicate divergence of basal lineages of ants near the Albian (ca. 10 5-110 Ma) when they presumably diverged from the Sphecomyrminae. Sphecomyrm ines are the plesiomorphic sister group to all other ants. or they are a pa raphyletic stem group ancestral to all other ants-they apparently became ex tinct in the Late Cretaceous. Ant abundance in major deposits of Cretaceous and Tertiary insects indicates that they did not become common and presuma bly dominant in terrestrial ecosystems until the Eocene (ca. 45 Ma). It is at this time that modern genera that form very large colonies (at least 10, 000 individuals) first appear. During the Cretaceous, eusocial termites, be es, and vespid wasps also first appear-they show a similar pattern of diver sification and proliferation in the Tertiary. The Cretaceous ants have furt her implications for interpreting distributions of modern ants.