title: Extreme Morphogenesis and Ecological Specialization among Cretaceous Basal Ants.
abstract: Ants comprise one lineage of the triumvirate of eusocial insects and experienced their early diversification within the Cretaceous [1-9]. Their ecological success is generally attributed to their remarkable social behavior. Not all ants cooperate in social hunting, however, and some of the most effective predatory ants are solitary hunters with powerful trap jaws [10]. Recent evolutionary studies predict that the early branching lineages of extant ants formed small colonies of ground-dwelling, solitary specialist predators [2, 5, 7, 11, 12], while some Cretaceous fossils suggest group recruitment and socially advanced behavior among stem-group ants [9]. We describe a trap-jaw ant from 99 million-year-old Burmese amber with head structures that presumably functioned as a highly specialized trap for large-bodied prey. These are a cephalic horn resulting from an extreme modification of the clypeus hitherto unseen among living and extinct ants and scythe-like mandibles that extend high above the head, both demonstrating the presence of exaggerated morphogenesis early among stem-group ants. The new ant belongs to the Haidomyrmecini, possibly the earliest ant lineage [9], and together these trap-jaw ants suggest that at least some of the earliest Formicidae were solitary specialist predators. With their peculiar adaptations, haidomyrmecines had a refined ecology shortly following the advent of ants.
authors.affiliation: CNRS UMR 6118 Géosciences & OSUR, Université Rennes 1, 35042 Rennes, France; Division of Entomology, Biodiversity Institute and Natural History Museum, University of Kansas, Lawrence, KS 66045, USA. Electronic address: vincent.perrichot@univ-rennes1.fr.
authors.forename: Vincent
authors.initials: V
authors.lastname: Perrichot
authors.affiliation: State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: bowang@nigpas.ac.cn.
authors.forename: Bo
authors.initials: B
authors.lastname: Wang
authors.affiliation: Division of Entomology, Biodiversity Institute and Natural History Museum, University of Kansas, Lawrence, KS 66045, USA; Department of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Engel
mesh_terms: D018647:Amber; D000818:Animals; D001000:Ants / Q000033:anatomy & histology*; D005075:Biological Evolution; D005580:Fossils / Q000033:anatomy & histology*; D009024:Morphogenesis; D002052:Myanmar; D012919:Social Behavior
chemical_list: D018647:Amber