View source for Haidomyrmecinae

{{Taxobox
|name = †Haidomyrmecini
|regnum = [[Animal]]ia
|phylum = [[Arthropod]]a
|classis = [[Insect]]a
|ordo = [[Hymenoptera]]
|familia = [[Formicidae]]
|subfamilia = †Haidomyrmecinae
|subfamilia_authority = Bolton, 2003
|diversity_link = :Category:List of species
|diversity = {{Genus Species Diversity|Fossil=only}}
}}

Hell ants, the haidomyrmecines, are a group of putatively predatory ants that are known exclusively from three Cretaceous amber deposits in France, Myanmar, and Canada. Hell ant cranial morphology is unlike any modern group of ants, a reflection of ancient diversification ultimately bound for extinction. Phylogenetic analyses have recovered haidomyrmecines as a stem-group lineage that diverged from modern ants prior to the most common recent ancestor of all living ants (Barden and Grimaldi, 2016; Barden et al., submitted). This phylogenetic placement, molecular divergence estimates (Moreau and Bell, 2013) and the presence of crown ants in Cretaceous amber (Grimaldi and Agosti, 2000; McKellar et al., 2013b; Zheng et al., 2018; Perrichot, 2019) indicate that hell ants and early members of extant lineages overlapped for tens of millions of years. The extinction of haidomyrmecines following their diversification remains an outstanding question in ant evolution, as is the function and evolutionary history responsible for this striking expansion into unparalleled phenotypic space. (Perrichot, Wang & Barden, 2020)
{{Photo Gallery
|name1=Perrichot, V., Wang, B. et al. 2020. New remarkable hell ants, Fig. 8.jpg
|size1=600px
|comment1=Artistic reconstructions of the heads of hell ants in lateral view, with mandibles in closed position. A, ''Haidomyrmex''. B, ''Protoceratomyrmex''. C, ''Aquilomyrmex''. D, ''Linguamyrmex''. E, ''Ceratomyrmex''. F, ''Chonidris''. G, ''Dhagnathos''. Scale bars: 0.5 mm. (From Perrichot et al. 2020.)
}}

==Identification==
Perrichot et al. (2020) - Defined by mandibles that are dorsoventrally expanded and highly modified heads with a variety of cranial appendages.

(females). Mandibles scythe- or sickle-shaped, with linear basal portion leading to an elongate and dorsally curved apical portion tapering, with inner margin usually developed in a triangular blade pointing medially and ventrally (exception in ''[[Aquilomyrmex]]'' where the inner margin is simple); mandibles uniquely articulating in a vertical plane oblique to longitudinal axis of body, in addition to a moderate lateral opening. Clypeus elongate, with anterior margin broadly concave, smooth, and lateral margins leading posteriorly to an elevated brushy lobe just ventral to antennal insertion, or to a horn expanded anteriorly between toruli. Antennae 12-segmented, filiform, usually with third antennomere longest of basal three flagellomeres (exceptions are in ''[[Haidomyrmex]]'' where fourth antennomere is longest, and in ''[[Haidomyrmodes]]'' where basal flagellomeres are of equal length). Petiole with a short anterior peduncule, nodiform. Gastral constriction between AIII and AIV generally present, faintly to deeply impressed. Pygidium simple, unarmed. Sting robust, dorsally curved. Legs with procoxa distinctly longer than meso- and metacoxae, with trochantellus present on mid- and hind legs; tibial spur formula 1-2-2, rarely 1-1-2, and tibiae additionally with 1e4 subapical, stout setae. In gynes, the fore wing with 8 closed cells, with cross-vein 1r-rs absent or incomplete (present as a short tubular or nebulous stub not reaching ScþR); cross-vein 2rs-m present, tubular; and crossvein cu-a arising from MþCu or Cu. Hind wing with jugal lobe present, with costal, basal and subbasal cells enclosed by tubular veins.

Even as Dlussky remarked on the unique cranio-mandibular system of hell ants, his bewilderment was related to a single taxon. Discoveries over the last decade and the taxa described here expand the boundaries of the group's morphology. Most striking is the extent to which the clypeus and mandibles are exaggerated. While all previously known hell ants possess cranial nodes or horns (Dlussky, 1996; Perrichot et al., 2008a, 2016; Barden and Grimaldi, 2012; McKellar et al., 2013a; Barden et al., 2017; Miao and Wang, 2019), these appendages are the product of elevations that originate in the posterior region of the clypeus in ''[[Haidomyrmex]]'', ''[[Haidomyrmodes]]'', ''[[Haidoterminus]]'', ''[[Ceratomyrmex]]'', and ''[[Linguamyrmex]]''. The clypeus itself is drawn out dorsoventrally, matching the elongation present in the head capsule. This scheme is echoed in ''Protoceratomyrmex''. However, the cranial horns present in ''[[Aquilomyrmex]]'', ''[[Chonidris]]'', and ''[[Dhagnathos]]'' are the product of an anterior clypeal margin that is extended dorsally as well as posteriad, resulting in a furrowed clypeal sclerite with a medial depression and ventrally concave horn. The visible epistomal sutures of ''Chonidris'' and ''Protoceratomyrmex'' highlight the two distinct cuticular origins of horns in ''haidomyrmecines''. In ''Aquilomyrmex'', the ventrally concave clypeus comprises the entire anterior expansion of the head capsule, and this expanded clypeus is matched by an equally extended labrum that is coated in thick denticles. The parallel modifications of the clypeus and mandibles in all ''haidomyrmecine'' taxa strongly suggest that these two features interacted during mouthpart movement, most likely to aid in prey capture.

{{AntWebImagesForTaxon|rank=subfamily}}
{{Subfamily identification keys}}

==Notes==
The first ''haidomyrmecine'' “hell ant” was unearthed in Northern Myanmar at least one hundred years ago. This early discovery is evidenced by the acquisition tag that accompanies the type specimen of ''[[Haidomyrmex cerberus]]'', the first described hell ant taxon. The tag (see AntWeb, 2019) indicates that R.C.J. Swinhoe sent T.D.A. Cockerell the specimen in 1920, as part of a series of amber collections that were sent to the Natural History Museum, London in the early 20th century (Cockerell, 1922). It would be another 76 years before the specimen was examined by Dlussky (1996), who described the enigmatic ant with muted astonishment, stating that ''Haidomyrmex'' differed “from all known Formicidae, both recent and fossil, by the very peculiar structure of the cranio-mandibular system.” Dlussky was referencing the unique scythe-like mandibles and elongated head capsule that characterize the many species of hell ants known today. The sole specimen worked by Dlussky was reexamined by Engel and Grimaldi (2005), who refigured ''H. cerberus'' and stressed the enigmatic nature of its morphology. Additional ''haidomyrmecine'' material was subsequently described as ''[[Haidomyrmodes mammuthus]]'' in Albian-Cenomanian age French amber, which confirmed that the unique cranial morphology of hell ants was present in more than one species (Perrichot et al., 2008a). Incidentally, because the inclusions present in French amber spanned both workers and alates, these ''haidomyrmecines'' also represent the earliest direct evidence of reproductive division of labor in ants (Perrichot et al., 2008b). Aside from ''H. mammuthus'', the majority of hell ants are recovered from Burmese amber, however, ''Haidoterminus cippus'' from Campanian-age Canadian amber in Alberta, extends the temporal range of ''haidomyrmecines'' at least 20 million years (McKellar et al., 2013a). A total of nine genera and 14 species are now described. All but two genera and three species have been discovered in the last ten years (circa 2020).

The unique cranio-mandibular complex and mesosomal structure of hell ants clearly distinguish them from other ant subfamilies as currently defined. Earlier studies suggested that haidomyrmecines may not belong to the Sphecomyrminae (Grimaldi et al., 1997; Perrichot et al., 2008a; McKellar et al., 2013a). But, at the time, there were few Cretaceous ant taxa for testing this hypothesis phylogenetically. Recently, the first phylogenetic analysis to include hell ants recovered all haidomyrmecine genera as a monophyletic group outside of modern and stem ant lineages, potentially sister to all other ants (Barden and Grimaldi, 2016). This result was supported by the highly aberrant morphology of hell ants, which is not seen in any other lineages, modern or extinct. Moreover, a recent phylogenetic analysis that included all hell ant genera, including new taxa described herein, recovered haidomyrmecines as each others' closest relatives and consistently monophyletic, to the exclusion of sphecomyrmine terminals
(Barden et al., submitted). In the same paper, a comparison of extant and Cretaceous morphospace also recovered haidomyrmecines as distinct from other stem and crown ants, while cranial morphospace overlaps among other stem ants and living taxa (Barden et al., submitted). There are no indications that scythe-like mandibles have evolved more than once, and so the monophyly of haidomyrmecines is best supported by this highly specific synapomorphy. In our view, the characteristic morphology of haidomyrmecines and strong evidence for their monophyly warrant the placement of hell ants in their own subfamily,  particularly as future paleontological work will undoubtably reveal more Cretaceous taxa.

==Evolution==
Perrichot et al. (2020) - Hell ant cranial morphology is unlike any modern group, a reflection of ancient diversification ultimately bound for extinction. Phylogenetic analyses have recovered ''haidomyrmecines'' as a stemgroup lineage that diverged from modern ants prior to the most common recent ancestor of all living ants (Barden and Grimaldi, 2016; Barden et al., submitted). This phylogenetic placement, molecular divergence estimates (Moreau and Bell, 2013) and the presence of crown ants in Cretaceous amber (Grimaldi and Agosti, 2000; McKellar et al., 2013b; Zheng et al., 2018; Perrichot, 2019) indicate that hell ants and early members of extant lineages overlapped for tens of millions of years. The extinction of haidomyrmecines following their diversification remains an outstanding question in ant evolution, as is the function and evolutionary history responsible for this striking expansion into unparalleled phenotypic space.

{{SubfamilyStatistics|{{Burmese amber}}, {{Charentese amber}}, {{Foremost Formation}}}}
{{ListOfTribesAndGenera}}

==Nomenclature==
{{Nomenclature}}
*†{{RedText|HAIDOMYRMECINI}} [tribe of †Sphecomyrminae]
**†Haidomyrmecini Bolton, 2003: 74, 261. Type-genus: †''Haidomyrmex'' Dlussky, 1996: 84.

Genera
===Taxonomic History===
*†Haidomyrmecini as tribe of †Sphecomyrminae: Bolton, 2003: 74, 261; Perrichot, et al. 2008: 92; McKellar, et al. 2013b: 457; Borysenko, 2017: 17.
*†Haidomyrmecinae as subfamily of Formicidae: Perrichot, Wang & Barden, 2020: 3.

===Taxonomic References===
McKellar, et al. 2013b: 457 (genera and all species key); Perrichot, Wang & Engel, 2016: in supplemental information (not paginated) (genera and all species key); Barden, et al. 2017: 838 (synopsis of species); Borysenko, 2017: 19 (diagnosis); Perrichot, Wang & Barden, 2020: 3 (status as subfamily).

==References==
*[[Media:Borysenko, L.H. 2017. Description of a new genus of primitive ants from Canadian amber, with the study of relationships between stem- and crown-group ants.pdf|Borysenko, L.H. 2017. Description of a new genus of primitive ants from Canadian amber, with the study of relationships between stem- and crown-group ants (Hymenoptera: Formicidae). Insecta Mundi 570: 1–57.]]
*[[Media:Boudinot, B.E., Perrichot, V. et al. 2020. †Camelosphecia gen. nov., lost ant-wasp intermediates from the mid-Cretaceous (10.3897@zookeys.1005.57629).pdf|Boudinot, B.E., Perrichot, V., Chaul, J.C.M. 2020. †''Camelosphecia'' gen. nov., lost ant-wasp intermediates from the mid-Cretaceous (Hymenoptera, Formicoidea). ZooKeys 1005, 21–55]] ({{doi|10.3897/zookeys.1005.57629}}).
*[[Media:Perrichot, V., Wang, B. et al. 2020. New remarkable hell ants (10.1016@j.cretres.2020.104381).pdf|Perrichot, V., Wang, B., Barden, P. 2020. New remarkable hell ants (Formicidae: Haidomyrmecinae stat. nov.) from mid-Cretaceous amber of northern Myanmar. Cretaceous Research 109, 104381]] ({{doi|10.1016/j.cretres.2020.104381}}).

[[category:Subfamily]][[category:Extinct subfamily]][[category:Haidomyrmecinae]]