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, 97 (25), 13678-83

A Formicine in New Jersey Cretaceous Amber (Hymenoptera: Formicidae) and Early Evolution of the Ants

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A Formicine in New Jersey Cretaceous Amber (Hymenoptera: Formicidae) and Early Evolution of the Ants

D Grimaldi et al. Proc Natl Acad Sci U S A.

Abstract

A worker ant preserved with microscopic detail has been discovered in Turonian-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 the large extant subfamily Formicinae, members of which use a defensive spray of formic acid. This specimen is the only Cretaceous record of the subfamily, and only two other fossil ants are known from the Cretaceous that unequivocally belong to an extant subfamily (Brownimecia and Canapone of the Ponerinae, in New Jersey and Canadian amber, respectively). In lieu of a cladogram of formicine genera, generalized morphology of this fossil suggests a basal position in the subfamily. Formicinae and Ponerinae in the mid Cretaceous indicate divergence of basal lineages of ants near the Albian (ca. 105-110 Ma) when they presumably diverged from the Sphecomyrminae. Sphecomyrmines are the plesiomorphic sister group to all other ants, or they are a paraphyletic stem group ancestral to all other ants-they apparently became extinct in the Late Cretaceous. Ant abundance in major deposits of Cretaceous and Tertiary insects indicates that they did not become common and presumably 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, bees, and vespid wasps also first appear-they show a similar pattern of diversification and proliferation in the Tertiary. The Cretaceous ants have further implications for interpreting distributions of modern ants.

Figures

Figure 1
Figure 1
Kyromyrma neffi holotype (AMNH NJ-1029) in New Jersey Cretaceous amber. Left lateral habitus of specimen in original position, showing propodeal spiracle and metapleural gland area; frontal view of head and dentition of mandibles; and detail of gaster apex, showing acidopore with fringe of hairs.
Figure 2
Figure 2
Cladogram of ant subfamilies, some tribes, the Cretaceous genera, and related families of aculeate wasps [from ref. (ants); and ref. for aculeate families]. The cladogram is overlaid on a geological time scale to show ages of fossils (numbered, in circles) and hypothesized dates of divergence. The thick circle (no. 13) is the formicine fossil in the present report. Unlike the prior (7) cladogram, the Sphecomyrminae here are shown as sister group to all other ants, based on the plesiomorphic scape. With the exception of compression fossils of Armaniidae and other families, the only ant fossils included are in amber, because preservation in amber allows accurate phylogenetic placement. Also not shown are several genera of ants in Burmese amber, of undetermined age within the Upper Cretaceous (36). Divergence times for some lineages are largely conjectural because of a paucity of fossils: clade of Apomyrminae and subordinate taxa, and the Myrmicinae + Pseudomyrmecinae clade. The Tertiary divergence time of the Australian clade of Myrmeciini + Nothomyrmeciinae is based on the post-Gondwanan isolation of Australia (35). Significant features of some clades are indicated. Circled numbers refer to the following fossils, deposits, and references. 1, Mesorhopalosoma cearae (Santana Formation, Brazil; ref. 37). 2, 3, Curiosivespa and Priorvespa spp. (Bon-Tsagan Nuur, Mongolia; Zaza Formation of Baissa). 4, Curiosivespa spp. (Kzyl-Zhar, Kazakhstan) and Symmorphus senex (Raritan Formation, New Jersey; nos. 2–4: ref. ; no. 4, ref. 38). 5, Archaeoscolia hispanica (Lleida, Cuenca, Spain; ref. 39). 6, Archaeoscolia senilis (Bon-Tsagan Nuur, Mongolia; ref. 40). 7, Cretaproscolia josai (Santana Formation, Brazil; ref. 39). 8, Cretoscolia promissiva (Ola' Formation, Magadan). 9, Cretoscolia patiens (Kzyl-Zhar, Kazakhstan; nos. 8 and 9, ref. 40). 10, Armania and Khetania spp. (Emanra Formation, Khabarovsk; ref. 41). 11, Armania (5). 12, Sphecomyrma freyi and sp. (Raritan Formation, New Jersey; refs. and 7). 13, Formicine fossil, this report (12). 14, Brownimecia clavata (Raritan Formation, New Jersey; ref. 7). 15, Cretomyrma spp., Dlusskyidris zherichini (Taimyr, Siberia; Baikura-Neru; ref. 4). 16, Sphecomyrma canadensis (Foremost Formation, Alberta; ref. 6). 17, Eotapinoma macalpini (Foremost Formation, Alberta; ref. ; placement uncertain). 18, Canapone dentata (Foremost Formation, Alberta; ref. 8). 19, Chimaeromyrma [Paleocene (?), Sakhalin Island]. 20, Aneuretellus [Paleocene (?), Sakhalin Island]. 21, Eotapinoma, Zherichinius [Paleocene (?), Sakhalin Island]. 22, Protopone (nos. 19–22; ref. 42). 23, Propalosoma gutierrezae (Klondike Mountain Formation, Washington; ref. 26). 24, Paleovespa baltica (Baltic amber). 25–31, Various genera of ants in subfamilies indicated (refs. , , and 43); Arkansas amber (Claiborne Formation; ref. 6). 32, Floriscolia relicta (Florissant, Colorado; ref. 40). 33, Pompilidae, genera indet., Dominican amber (D.G., unpublished observation). 34, Agelaia electra (Dominican amber; ref. 44). 35–41, Various genera of ants in subfamilies indicated (Dominican amber; ref. 45). Not all Tertiary fossils of Pompilidae and Vespidae are indicated; no Cretaceous fossils of Pompilidae or any fossils of Bradynobaenidae are known. Ma, mega-annum; K/T, Cretaceous/Tertiary; J/K, Jurassic/Cretaceous.

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