Ants (Hymenoptera, Formicidae) through space, time, and sociality : a history from amber.
With over 13,000 ecologically diverse species exhibiting worldwide ubiquity in vegetated terrestrial ecosystems, ants are one of nature's greatest success stories. Colonies range from a few dozen tiny workers housed inside of an acorn to millions of nomadic army ants known to consume even vertebrates. The ant fossil record is very rich, comprising thousands of amber and impression specimens spanning a hundred million years, the vast majority of which is Cenozoic. Until very recently, early ant history has been obfuscated by a lack of well-preserved fossils from the Cretaceous. Here, utilizing CT-scanning methodology and traditional methods, diverse species of ~99 million-year-old Cretaceous ants are described from Burmese amber, which together comprise over one-third of all known Cretaceous ants. Among them are trap-jaw predators with scythelike mandibles not known in any living or extinct ants, as well as enigmatic feeders with hair-coated mouthparts, and several species with morphology analogous to that found in modern ants while retaining plesiomorphic features. These and other unusual Cretaceous taxa are contextualized for the first time, with results that challenge traditional viewpoints regarding the diversity, phylogenetic placement, and sociality of the earliest ants known. In the age of molecular phylogenetics the role of fossils can be unclear. Most frequently, fossils are included in analyses solely as calibration points for divergence date estimates, a practice that relies on assumed taxonomy and excludes biogeographic information. To explore alternative roles for fossils in molecular-based biogeographic, phylogenetic, and temporal reconstruction, combined analysis methodology is explored -- first, with respect to a small genus, and then finally applied to a large sampling of all ant subfamilies. The genus Leptomyrmex is endemic to eastern Australia, New Caledonia and New Guinea. Over 25 years ago, a putative fossil Leptomyrmex was described from Dominican amber dated to the Miocene. In the absence of compelling evidence other than taxonomic discussions in literature, researchers have typically excluded the Dominican fossil from phylogenetic and biogeographic reconstruction. To test the placement of the fossil, published molecular sequences for modern Leptomyrmex and related groups were merged with a novel morphological matrix. Through combined analysis the fossil was recovered among modern Australasian Leptomyrmex, indicating that the current distribution is a reflection of a great contraction and more complex biogeographic history. This same methodology is applied to a much larger dataset including members of all modern ant subfamilies in a preliminary total-evidence analysis of ants.
viii, 236 pages : illustrations (chiefly color)
Ants, Fossil., Amber fossils.