Gesomyrmex hoernesi Mayr

Dlussky, G. M., Wappler, T. & Wedmann, S., 2009, Fossil ants of the genus Gesomyrmex Mayr (Hymenoptera, Formicidae) from the Eocene of Europe and remarks on the evolution of arboreal ant communities., Zootaxa 2031, pp. 1-20 : 6-9

Gesomyrmex hoernesi Mayr , 1868

(Fig. 2 and Fig. 6A-E)

Gesomyrmex hoernesi Mayr , 1868, p. 52, tab. II, fig. 38-41 (worker and male); Ern. Andre, 1895, p. 82; Handlirsch, 1907, p. 859.

Gesomyrmex hoernesii Mayr : Dalla Torre, 1893, p. 176 (misspelling).

Gesomyrmex hoernesi Mayr : Wheeler, 1915, p. 108-111, fig. 53; Wheeler, 1929, p. 11; Burnham, 1978, p.114;

Ponomarenko, Schultz, 1988, p. 26; Bolton, 1995, p. 207; Dlussky, 1997, p. 59, fig. 3h.

Dimorphomyrmex theryi Emery , 1905, p. 188, fig. 1 (worker); Handlirsch, 1907, p. 868; Wheeler, 1915, p. 104-106, fig. 50; Burnham, 1978, p.113. Synonymy by Wheeler, 1929, p. 11.

Dimorphomyrmex mayri Wheeler , 1915, p. 106-107, fig. 51 (worker); Burnham, 1978, p.113. Synonymy by Wheeler, 1929, p. 11.

Gesomyrmex annectens Wheeler , 1915, p. 107-108, fig. 52 (worker); Burnham, 1978, p.113. Synonymy by Wheeler, 1929, p. 11.

Types. Mayr (1868) described G. hoernesi from 18 workers and a male. Three workers are preserved in NMW (1984/34/141, 1984/34/142 and 1984/34/143). A lectotype was not designated. The holotype of Dimorphomyrmex theryi is present at the collection of BMNH (In.29052). The types of Gesomyrmex annectens and Dimorhomyrmex mayri are lost.

Studied material. Baltic amber (workers). BMNH.In.17787 with label "Samland"; BMNH.In.29052 with label "Coll. A. Thery, holotype of Dimorphomyrmex theryi Emery "; GMUG.BST.03830 (K2614) determined by Wheeler (1929) as G. hoernesi ; GMUG.BST.03840 (K2626); GMUG.BST.03977 (228, K4302); GMUG.BST.03993 (K4048); GMUG.BST.04076 (K6406); GMUG.BST.04088 (a181, K4311); GMUG.BST.04097 (x10); GMUG.BST.04151 (K4442) determined by Wheeler as D. theryi ; GMUG.BST.04152 (K4252) determined by Wheeler as D. theryi , pictured on fig. 50 in Wheeler (1915); GMUG.BST.04157 (K779) determined by Wheeler as D. theryi ; GMUG.BST.04200 (a124) determined by Wheeler as G hoernesi ; GMUG.BST.04206 (a119) determined by Wheeler as G hoernesi ; GMUG.BST.04207 (K889) determined by Wheeler as G. hoernesi ; GMUG.BST.04208 (a111) determined by Wheeler as G hoernesi ; GMUG.BST.04213 (K4466) determined by Wheeler as G hoernesi ; GMUG.BST.04214 (a95) determined by Wheeler as G hoernesi ; GMUG.BST.04438 (K6421) determined by Wheeler as D. theryi ; GMUG.BST.04456 (a204) determined by Wheeler as G hoernesi ; GMUG.BST.04457 (a171) determined by Wheeler as G. hoernesi ; MZPW.412; MZPW.2940; MZPW.5864; MZPW.5890; MZPW.8126; MZPW.9561; MZPW.10353; MZPW.15933; MZPW.15980; MZPW.19144; MZPW.19377; MZPW.19959; PIN.964/484; PIN.964/485; PIN964/486; CGC.1632; CGC.2652; CGC.3338. Bitterfeld amber. PMHU.7/201 (worker); HM.7/229 ([[queen]]); PMHU.10/225 (worker); PMHU.11/221 (worker); PMHU.13/206 (worker); PMHU.13/210 (worker); PMHU.13/221 (worker); PMHU.15/205 (worker); PMHU.16/227; MKC.F-010 [[male]]); MKC.F-129 (worker); MKC.F-130 (worker). Rovno amber (workers). SIZK.K-419; SIZK.K-5695. Scandinavian amber (workers). ZMUC.187 with label "G. Henningsen, 01.07.1966"; ZMUC.188 with label "G.V. Henningsen, 01.02.1969"; ZMUC.189 with label "G.V. Henningsen, 03.05.1960"; ZMUC.190 with label "A. K. Andersen, 28.03.1968".

Description. Minor worker. BL 2.5-5 mm. Body slender. Head longer than broad, subtrapezoid, narrower in the front than in the back, with convex sides, rounded posterior corners and feebly concave posterior border. Eyes very large, convex, reniform; long axes of eyes distinctive convergent anteriorly. Maximum eye diameter 1.8-2.0 times less than head length and 1.05-1.8 times less than head width. Cheeks very short. Ocelli small but distinct. Frontal area and frontal groove obsolete. Clypeus as long as broad or a little longer than broad. Anterior clypeal margin projecting as a long, rather narrowly rounded lobe over the bases of the mandibles. Antenna short, 8-jointed. Scape does not reach the posterior margin of the eye. Funiculus incrassate, but without distinct club. First funicular joint more than twice as long than thick. The following joints longer than thick. Mandibles very long, decussating when closed, with 9 long, acute teeth, some of which are slightly shorter than the others. External margin of mandible concave in middle part. Maxillary palps do not reach the occipital foramen. Mesosoma long, narrower than the head, constricted in the mesopropodeal region. Pronotum gradually convex, longer than broad. Mesonotum rather flat above, the latter compressed laterally, longer than broad, narrower behind than in front and impressed, but without a suture that divides it from the metanotum. In lateral view propodeal dorsum and declivity are subequal and form a rounded obtuse angle; propodeal dorsum feebly convex, propodeal declivity slightly concave. Legs rather slender. Middle and hind tibiae each with one short simple spur. Petiole as long as broad, with low and thick scale, a little more than twice as broad as long, rounded above, with convex anterior and posterior surfaces. Gaster elongate elliptical, with a circlet of coarse anal cilia. Body rather shiny and lightly shagreened. Mandibles, clypeus and frons usually delicately longitudinally striated. Erect hairs absent on all parts of the body except the top of the gaster. Decumbent pubescence absent.

Major worker (soldier). BL 5-8 mm. Head a little longer than broad, subrectangular, a little narrower in the front than in the back, with straight sides, rounded posterior corners and straight or feebly concave posterior border. Eyes large and convex, elongate elliptical or slightly reniform, situated near the middle of the sides, slightly more approximated in the front than in the back. Maximum eye diameter 2-3 times less than head length and 1.8-3.5 times less than head width. Ocelli usually lacking. Frontal carinae short but prominent, extending to the middle of the anterior orbits. Frontal area small and indistinct. Clypeus broader than long, its posterior border extending back medially between the frontal carinae. Anterior clypeal border projecting in the form of a short broad rounded lobe. Antenna short 8-jointed. Scape not reaching to the posterior orbits. Funiculus incrassated but without distinct clave; joints 1 and 2 of the funiculi subequal, about twice as long as thick, joints 3 and 4 about 1.5 times as long as thick, 5 and 6 scarcely longer than thick, the terminal joint a little longer than thick. Mandibles stout, not decussating when closed, with convex external margin and 8 to 9-toothed masticatory margin. The teeth are stout; the apical tooth is longest; shorter teeth are alternating with the longer ones towards the base. Maxillary palps short, do not reach the occipital foramen. Mesosoma long, narrower than the head, constricted in the mesopropodeal region. Pronotum gradually convex, about as long as broad. Mesonotum longer than broad and broader in front than behind; laterally its surface is straight and gradually sloping backward, its sides compressed. Metanotum distinct, short and transverse, divided from mesonotum and propodeum by sutures or impressions. In lateral view propodeal dorsum and declivity are subequal and form a rounded obtuse angle; propodeal dorsum feebly convex, propodeal declivity slightly concave. Legs long and rather stout, middle and hind tibiae with short simple spurs. Petiole short, with a low and thick scale. Gaster elongate oval. Body rather shiny and lightly shagreened. Mandibles, clypeus and frons sharply and densely longitudinally striated. Erect hairs absent on all parts of the body except the top of the gaster. Decumbent pubescence absent.

Gyne (first description). BL 10.5 mm. Head subrectangular, about 1.3 times longer than wide, with rounded posterolateral corners and feebly concave posterior margin. Eyes comparatively smaller than in workers: maximum eye diameter less than 4 times head length. Ocelli large, distance between central and lateral ocelli equals roughly their diameters. Anterior clypeal margin and dentition of mandibles not visible. Antenna 10-jointed. Scape does not reach the posterior margin. Funiculus incrassate, but without distinct club. First funicular joint longer than 2 and 3 together and 2.5 times longer than thick. Following joints except terminal about as long as thick. Scutum and scutellum wider than long. Gaster, petiole and propodeum covered by white film and not visible. Head and mesosoma with numerous short erect hairs. Legs without erect and semi-erect hairs.

Male. BL 7-8 mm. Head with enormous large convex eyes, which occupy most of the head. Ocelli large and convex. Frontal carinae and lobes absent. Frontal furrow distinct. Anterior clypeal margin projecting as a rounded lobe. Antenna geniculate, small. Mayr (1868) wrote that it is 11-jointed but the studied specimen has only one antenna with 8 joints; perhaps the terminal joints were lost. Mandibles short, not opposable, with an acute apical tooth and without teeth on the masticatory margin. Maxillary palps long, reach the occipital foramen. Pronotum transverse. Scutum with flat dorsal surface strongly rounded anteriorly. Scutellum convex. Propodeal dorsum and declivity form rounded obtuse angle in lateral view; propodeal dorsum much shorter than declivity. Legs rather long and thin. Petiole with rounded scale, higher than long. Gaster cylindrical. Genitalia not retractile.

Body shiny with very delicate shagreened sculpture. Short erect hairs present on mandibles, clypeus, near ocelli, on the last sternites of the gaster, and genital parts. Decumbent pubescence absent.

Forewing with closed cells 1+2r, 3r and mcu. Cell mcu rhomboidal. Veins RS and M partly united and form short section RS+M.

Measurements (in mm). Minor workers. CGC.1632: BL 5.0, AL 1.7, HL 1.2, MdL 0.64, ED 0.61, SL 0.58; CGC.3338: BL 2.3, AL 0.73, HL 0.60, MdL 0.32, ED 0.31, SL 0.30; GMUG.BST.03840: BL 4.7, AL 1.5, HL 1.0, ED 0.52, PtL 0.35. PtH 0.41; GMUG.BST.04206: BL 4.4, AL 1.5, HL 1.0; GMUG.BST.04207: BL 3.9, AL 1.3, HL 0.95, HW 0.68, MdL 0.50, ED 0.50, SL 0.52; GMUG.BST. 04208: BL 4.1, AL 1.35, HL 1.05, HW 0.75, MdL 0.50, ED 0.58, SL 0.48; GMUG.BST.04213: BL 5.0, AL 1.5; GMUG.BST.04214: BL 4.35, AL 1.4, HL 1.1, ED 0.58; GMUG.BST.04456: BL 4.8, AL 1.55, HL 1.1, HW 0.8, ED 0.58, SL 0.55; PIN.964/484: HL 0.99, HW 0.56, MdL 0.53, ED 0.53, SL 0.51; PIN.964/485: BL 5.5, AL 1.75, HL 1.2, HW 1.1, ED 0.61, SL 0.64, PtL 0.35, PtW 0.45, PtH 0.48; PIN.964/486: BL 5.5, AL 1.75. Major workers. GMUG.BST.04151: BL 5.7; GMUG.BST.04152: BL 5.8, AL 1.7, HL 1.4, HW 1.3, MdL 0.57, ED 0.47, SL 0.53; GMUG.BST.04157: BL 5.3, AL 1.9; PMHU.13/221: BL 5.3; BMNH.In.29052: BL 5.5, AL 1.75, HL 1.25, HW 1.25, ED 0.53, SL 0.50; SIZK.K-419: AL ~1.8, HL 1.2, HW 1.1, ED 0.62, SL 0.58. Gyne. PMHU.7/229: BL 10.5, AL ~3, HL 2.2, HW ~1.6, ED 0.46, SL 0.92, FWL 6.5. Male. MKC.F-010: BL about 7, AL 3.0, HL 1.3, MdL 0.36, ED 1.01, SL 0.34, FWL 6.8.

Distribution and horizon. Baltic, Bitterfeld, Rovno and Scandinavian ambers. Late Eocene.

Comments. There is a problem with the association of different castes of fossil ant species as findings of males, females and workers of the same species in the same piece of amber are extremely rare. However we are confident that workers, male and female of Gesomyrmex described above belong to the same species. Up to the present 231workers of Gesomyrmex from Baltic and similar ambers are studied: 18 by Mayr (1868), 7 by Andre (1895), one by Emery (1905), 172 by Wheeler (1915) and 33 (excluding species determined by Wheeler) by one of us (GMD). All these specimens belong to the same species G hoernesi . So there is a high possibility that the two studied males (one by Mayr, and one by us) and above described gyne belong to the same species. The gyne has small eyes relative to those of the workers. This is unusual for ants, but Gesomyrmex is evidently an exception to the rule. The only extant species whose workers and gynes are known is G. luzonensis (Wheeler, 1916, 1930). Its gynes have comparatively smaller eyes than workers.

Theobald (1937, p. 212) described Gesomyrmex hoernesi from Oligocene deposits of France (Kleinkembs, Haut-Rhin). Judged by the description and figures the described insects are really ants but they do not belong to Gesomyrmex . The male (Theobald 1937, pl. XIV, fig. 24) has a low nodiform petiole and filiform (not geniculate) antenna with a very short scape, and evidently belongs to Dolichoderinae . One of two specimens described as gynes (Theobald 1937, pl. XIV, fig. 25) has a rounded head and triangulate petiole without a scale. The form of the head of the other «gyne» (Theobald 1937, pl. XIV, fig. 26) is similar to Formica or Camponotus , but not to Gesomyrmex . This specimen also has a small and narrow petiole without a scale. Specimens described as workers (Theobald 1937, pl. XIV, figs. 27, 28) judged by the construction of mesosoma really are poorly preserved gynes without wings. They also have no characters of Gesomyrmex .