Gerontoformica

Phillip Barden & David A. Grimaldi, 2016, Adaptive Radiation in Socially Advanced Stem-Group Ants from the Cretaceous, Current Biology 26, pp. 515-521 : 539

Description (gyne) Gerontoformica sp.: JZC Bu313

(Figs. S3F; S4D-F)

This is a virtually complete specimen in a piece that was originally bead-shaped, with a hole bored through it. It was trimmed flat on two faces, one face providing a full frontal view of the head; size is now 8 x 5 x 4 mm. The ant is missing its apical antennomeres (just the four basal ones remain), and the apex of the metasoma (e.g., sting), which were obliterated at the surface of the bead. The piece also contains a Collembola , a small Hemiptera (Dipsocoromorpha), and a tiny empidoid fly (the first two of these suggests capture near or on the surface of the ground). Other than loss of some small portions the ant is quite well preserved, with little preservational distortion and the cuticle cleared in most regions (thus facilitating observation of fine details). The wings are particularly well preserved.

Head length 0.81; head width 0.62; eye length 0.20; mesosomal length 1.89 (likely distorted by dessication); petiole length 0.54; gaster length (preserved portion) 1.73; forewing length 4.25, width 1.34; hindwing length 2.83, width 1.06. Head: oral margin broad, with comb of ca. 18 clypeal pegs; mandible structure typical of Gerontoformica : broad, with single preapical tooth (plus apical one). Ocelli present, small; head with numerous fine, erect setae; bases of antennae surrounded by large, round, shallowly concave area. Pronotum projected into long, narrowed neck; metapleural gland opening large, facing posteriad (mesosoma strongly compressed laterally). Mesoscutellum and postnotum well developed; propodeum shallow, sloping; petiole distorted, not fully discernable. Protibia with long, slender, bare (non-pectinate) calcar having bifid apex, smaller spur mesally (0.5x the length). Mesotibia with slender ventroapical spur; metatibia with pair of ventroapical spurs (approximately equal in size).

Wing and Venation: Hind wing with row of six thicker hamuli distal to Rs; 3 finer, widely spaced ones distal to this. Venation very similar to that of male Sphecomyrma sp. in Turonian-aged New Jersey amber (AMNH NJ-242) [S1]. Main forewing differences are that Gerontoformica sp. (Bu313) has a partial division of cell SMC1, as in Baikurus mandibularis Dlussky (vs. undivided); basal cells BC and SBC are shorter; vein Cu1 is present, though weaker than the other veins (vs. absent); vein M gradually fades apicad but nearly complete (vs. evanescent well before the wing margin). Main hind wing differences are Rs and M evanescent apically (vs. barely developed in Sphecomyrma ).