Gesomyrmex gallicus

Identification
This species is readily distinguishable from all extant and extinct species by its petiolar node with dorsal margin acute instead of rounded in profile view; and from all species except the extinct Gesomyrmex hoernesi by the masticatory margin of mandibles with nine teeth. It differs from the latter by its external mandibular margins (sensu Richter et al. (2019)) straight to feebly convex in full-face view (medially concave in G. hoernesi), and the petiolar node with dorsal margin medially concave (flat or weakly convex in G. hoernesi).

Workers of G. gallicus share a diagnostic nine-toothed mandible with Gesomyrmex hoernesi, contrasting with the five, six or eight teeth in workers of extant species (when known), but differs from G. hoernesi in its straight to slightly convex external mandibular margins (vs medially concave), which is more similar to extant species (Fig. 3). Gesomyrmex gallicus also differs from G. hoernesi and all extant species in its petiolar node with dorsal margin angled between anterior and posterior faces (vs rounded), and from G. hoernesi, Gesomyrmex chaperi, Gesomyrmex howardi or Gesomyrmex luzonensis in its petiolar node with dorsal margin emarginate medially (vs flat or slightly convex) (Fig. 3). Based on the findings by Peeters et al. (2017), we assign the new larger morph to a soldier cast. A ‘supersoldier’ would be characteristically defined by a sub-rectangular head and relatively smaller eyes. Additionally, this species differs from all other known Gesomyrmex species by its temporal range.

Distribution
This taxon was described from.

Nomenclature

 * †. †Gesomyrmex gallicus Aria et al., 2023: 2, figs. 1-3, Supp. Figs. 1-2 (w.) FRANCE (Oligocene).

Type Material

 * Holotype MNHN.F.A32941 (minor worker), Le Quesnoy farm, commune of Chevrière, near Creil, department of Oise, France; Lower Eocene (Ypresian), level MP7 of the mammal fauna of Dormaal.
 * Paratypes MNHN.F.A32938 (major worker), MNHN.F.A32939 (minor worker), MNHN.F.A32940 (minor worker), same data as holotype.

Taxonomic Notes
Théobald (1937) described a series of specimens from Eocene–Oligocene rock-imprints of Kleinkems (Germany) he assigned to the genus Gesomyrmex, but this type material was subsequently lost and the description precludes their confident placement within this genus. The alate specimen illustrated by Théobald (1937: pl. XIV, fig. 22) has a wing venation strikingly different from that of the other representatives of the genus, inter alia because of the absence of the vein Rs distad pterostigma and of the small rhomboidal along RsþM. Therefore, the species is considered as incertae sedis in Formicidae (Dlussky et al. 2009). Species erected based on gynes from Eocene and Miocene compression deposits (Dlussky et al. 2009, 2015) also require a critical reappraisal, developed hereafter.