Dhagnathos autokrator

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Dhagnathos autokrator
Temporal range: Early Cenomanian, Late Cretaceous Burmese amber, Kachin State, Myanmar
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Haidomyrmecinae
Genus: Dhagnathos
Species: D. autokrator
Binomial name
Dhagnathos autokrator
Perrichot, Wang & Barden, 2020

Dhagnathos autokrator F2a.jpg

Identification

As for the genus, by monotypy.

Distribution

This taxon was described from Burmese amber, Kachin State, Myanmar (Early Cenomanian, Late Cretaceous).

Castes

Known from gynes.

Specimens

Figure 3. Overview and details of alate females (gynes) of Dhagnathos autokrator gen. et sp. nov. Specimen HA03 (A), specimen XA01 (B), specimen RM1 (C–D), and holotype IGR.BU-003 (E–G). Habitus (A, B, C), fore wing (D), mandibles, clypeus and labrum in lateral views (E, F), wings, propodeum and petiole (G). Abbreviations: cc, lateral clypeal carina; cd, clypeal denticles; cp, clypeal process (horn); lss, labral spine-like setae; mib, mandibular medioventral blade; mp, mesal process of 1st gastral sternite; pdr, propodeal ridge; spp, sub-petiolar process. Scale bars: 2 mm (A–C), 1 mm (D, G), 0.5 mm (E, F).

Originating from amber mines located near Noije Bum Village, Tanai Town, Myitkina District of Kachin State, northern Myanmar. A radiometric dating of zircons from the amber-bearing bed gave a maximum age of 98.79 ± 0.62 Ma (Shi et al., 2012), thus corresponding to the latest Albiane-earliest Cenomanian (mid-Cretaceous), which may not be very different from the age of the amber itself (Smith and Ross, 2018; Yu et al., 2019).

Holotype IGR.BU-003. Alate gyne. Preserved without distortion, but missing right antennomeres XI-XII, left antennomeres IV-XII, apical portion of fore wings, portion of all right legs beyond femur, portion of left fore leg beyond tarsomere II and left hind leg beyond trochanter, and apico-dorsal portions of gaster beyond AIV. The amber piece is crossed by an internal fracture running obliquely to the head through the left compound eye, scapes, medioapical portion of the horn, and lower portion of the right gena. The piece broke at the level of this fracture during polishing, so the two fragments were immediately glued together. Originally preserved with a thrips (Thysanoptera), now in a separate fragment measuring 14.4 x 10 x 6 mm. IGR, Geology Department and Museum of the University, Rennes 1, France.

HA03. Alate gyne. An almost complete specimen exposed in profile views, with slight lateral compression, partly covered with bubbles on its right side, missing right antennomeres V-XII, left antennomeres III and V-XII, the right fore leg and left mid leg beyond femur. In a round piece of clear yellow amber measuring 15 x 5 mm. HA, Huangyiren Amber Museum, Taiwan.

XA01. Alate gyne. A specimen exposed in profile views, with distinct distortion affecting the head capsule and mesosoma, missing right antennomeres V-XII, left antennomeres IV-XII, most of legs beyond coxae, and apical portions of wings and gaster. Petiole and preserved anterior portion of gaster entirely concealed by wings. In a rounded piece of clear yellow amber measuring 20 x 7 mm, with a midge (Diptera). XA, Lingpoge Amber Museum, Shanghai, China.

RM1. Alate gyne. A complete specimen exposed mostly in right lateroventral view, apparently weakly distorted but largely obscured by small bubbles contacting the body, organic debris floating in amber matrix, and internal fractures crossing the amber piece. In a rounded piece of clear yellow amber measuring 39 x 26 x 8 mm, with a psychodid fly (Diptera) and numerous domichnia (borings) from pholadid bivalves. RM, Ruipoxuan Museum, Jinan, China.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

  • autokrator. †Dhagnathos autokrator Perrichot, Wang & Barden, 2020: 5, figs. 2A-C, 3, 8G (q.) MYANMAR (Burmese amber).

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Queen

holotype IGR.BU-003, in mm: HL 2.50; HoL ca. 1.70; EL 1.20; ocelli diameter 0.20; MDbL 0.40, MDtL 0.55, MDaL 2.00; length/width of antennomeres: I (scape) 1.15/0.16, II (pedicel) 0.26/ 0.14, III 2.16/0.10, IV 1.50/0.07, V 1.34/0.07; WL 3.85; FWL (as preserved) 6.35 (7.90 on specimen DHA4); PL 1.84, PH 1.00, PW 0.67.

Body length ca. 14 mm. Cuticle generally smooth, without distinct sculpturing, sparsely covered by thin, long, erect setae, the head additionally densely covered by short, adpressed setae on vertex and genae.

Head only slightly longer than high and wide. Vertex and posteroventral surface rounded, anterior surface relatively flat, and genae shorter than eyes and projecting anteroventrally above mandible insertion into a cheek-like lobe. Ocelli present near top of vertex, conspicuous, ocellar diameter slightly larger than width of first antennomere; interocellar distance about half of ocellar diameter. Compound eyes bulging, reniform, 2.4 x as long as wide, situated posteriorly on head (EPI 440). Antennae inserted between compound eyes around their midlength, closely flanking lateral edges of clypeus; base of antenna with basal bulb exposed, inserted within thick annular torulus. Antenna geniculate, filiform; scape short, 0.5 x head length, weakly arched and broadened apically; first funicular article (pedicel) very short, 0.22 x scape length, less than twice as long as wide, broadened apically; flagellomeres unusually slender, funicular article II (antennomere III) about 22 x as long as wide; following antennomeres gradually decreasing in length and width. Posterior clypeal margin apparently fused, while horn is the result of de novo medial margin/ridge; anterior clypeal margin broadly rounded. Clypeal horn directed upward for its basal quarter, then bent at a right angle and directed forward for remaining length; horn gently rounded apically, without expanded lobe; dorsal surface of horn convex; ventral surface emarginate, its lateral margins prominent and prolonged basally into raised frontal carinae diverging anteriorly to reach the anterior margin of head, just above insertion of mandibles. Setation of horn consisting, on ventral surface, of a dense brush of short, peg-like denticles at apex; similar peg-like denticles widely spaced and arranged in a single row on each lateral margin, and becoming progressively denser and arranged in 2-3 longitudinal rows along lateral clypeal carinae; dorsal and ventral surfaces of horn sparsely covered by thin, long, erect setae. Labrum well exposed, large, nearly trapezoid, with anterior margin convex, posterior margin slightly emarginate medially, sides unsutured to clypeus so that anterior part of labrum is apparently movable; dorsal surface of labrum rimmed laterally by a longitudinal brush of stiff, spine-like setae, also densely coated by thin, erect setae becoming progressively longer and stiffer along lateral and posterior margins. Mandibles long (MDI 97), scythe-shaped, widely spaced basally and converging apically, with tips curved and acute, nearly reaching the rounded portion of the horn as preserved; basal portion linear, short; apical portion 5 x as long as basal portion, curved dorsally and posteriorly, with dorsal surface concave and rimmed on each margin by row of acute teeth and thin, erect setae directed backwards; medioventral blade between basal and apical portions forming a large, isosceles, blunt tooth perpendicular to apical portion. Palps long (visible on specimen HA03), coated dorsally in fine, tapered setae, maxillary palp with 6 segments, as long as head capsule when combined; labial palp with 5 segments.

Mesosoma. Pronotal colar pronounced, concealing propleuron in dorsal view, separated from remaining pronotal dorsum by a distinct transverse ridge; pronotal dorsum strongly concave immediately anterior to ridge, nearly flat posterior to ridge; promesonotal suture deeply impressed. Mesoscutum as long as pronotum (excluding neck) in dorsal view, about as broad as long; mesoscutal dorsal outline feebly convex, with long parapsidal furrows almost reaching anterior mesonotal margin, converging posteriorly but not touching. Mesoscutellum posteriorly expanded, in dorsal view concealing median portion of metanotum; dorsal and posterior mesoscutellar surfaces concave, their junction forming a sharp angle; dorsal mesoscutellar surface with a deep, broad, transverse groove immediately posterior to scuto-scutellar suture. Metanotum medially as high as long, with posterior surface forming distinct angle with pronotal dorsum. Propodeum 1.25 x as high as long, dorsal and declivitous surfaces meet at pronounced right angle, forming conspicuous ridge; dorsal surface nearly flat, declivitous surface faintly concave; propodeal spiracle slit-like, opening posteriad, at junction of propodeal dorsum and sides; metapleural gland orifice opening laterally, protected by guard setae. Legs long and robust (mostly visible on specimen HA03); mesocoxa distinctly shorter than pro-and metacoxae; small trochantellus present on mid- and hind legs; all femora distinctly swollen in their basal half, tibiae swollen in their apical half; ventral margin of protibia apically with large calcar gently curved, protibia possessing small subapical point, and two straight, stout setae less than half as long as calcar; mesotibia apically with two long, straight, pectinate spurs, and two short, stout setae; metatibia apically with one long, pectinate spur and one long, simple spur; tarsomeres IeIV of all legs with pairs of stout setae along entire ventral surface (8-10 pairs on tI, 4-5 pairs on tII, 3 pairs on tIII, 2 pairs on tIV), and apically with 2 pairs of stout setae each flanking a spatulate spine; additionally the ventral surface of tarsomeres IeIV covered by dense brush of thin, erect setae; pretarsal claws strong, with a distinct subapical tooth.

Fore wing with Rs∙f2, basal portion of Rs∙f3, M∙f4, and Cu1 nebulous, all other veins tubular; pterostigma elongate, ca. 6 x as long as broad; a short stub of cross-vein 1r-rs present, nebulous; Rs∙f1 half as long as M∙f1, both distinctly arched; Rs∙f2 and Rs∙f3 nearly at right angle, Rs∙f2 half as long as M∙f2; 2rs-m present, situated beyond apex of pterostigma; discal and subdiscal cells pentagonal; cu-a arising from MþCu and proximal to M∙f1 (Cu∙f1 short); vein Cu with both Cu1 and Cu2 present. Hind wing with jugal lobe present; anterior margin with 5 median and 22 distal hamuli; vein C present; vein R present, reaching distal wing margin; Rs∙f1 more than twice as long as 1rs-m; cu-a arising from M+Cu, proximal to fork of M∙f1 and Cu (Cu∙f1 short); Rs∙f2, M∙f2, Cu, and A∙f2 present, not reaching wing margin.

Metasoma with petiole short-pedunculate, almost 0.6 x as high as long; petiolar tergite a broadly convex node, with anterior surface approximately twice as long as posterior face; subpetiolar process present, in profile forming a high, transverse, lamella pointing ventrally, with anterior face concave, posterior face vertical; not fused tergosternally, suture visible; attaching broadly to gaster. Gaster elongate. First gastral tergite with helcium pronounced, forming a post-petiolar peduncle, with anterior surface behind helcium high, oblique, and dorsal surface strongly convex, short; anteriormost part of first gastral sternite with a distinct mesal process (keel) pointing anteroventrally below helcium.

Second gastral segment distinctly longer than first, with presclerite largely exposed to form a deep, broad constriction between first and second gastral segments (abdominal segments III and IV). Gastral segments unfused with deep lateral suture. Following segments poorly preserved, pygidium apparently broadly acute towards sting shaft.

Type Material

IGR.BU-003, alate female. Additional specimens. HA03, XA01 and RM1, three alate females. Horizon and locality. Upper Cretaceous, upper Albiane-lower Cenomanian (ca. 99 Ma); in amber from the Hukawng Valley, Kachin State, Myanmar. Holotype: IGR, Geology Department and Museum of the University. Rennes 1, France.

Etymology

The specific epithet refers to autokrátor (Greek, meaning ‘self-ruler’), an individual who exercises absolute power, unrestrained by superiors; in reference to the highly powerful aspect of this ant.

References