Gracilidris humilioides (Wilson, Wild, A. L. & Cuezzo, F., 2006

Wild, A. L. & Cuezzo, F., 2006, Rediscovery of a fossil dolichoderine ant lineage (Hymenoptera: Formicidae: Dolichoderinae) and a description of a new genus from South America., Zootaxa 1142, pp. 57-68 : 66-68

Gracilidris humilioides (Wilson 1985), comb. nov.

(Figs. 12-14)

Iridomyrmex humilioides Wilson 1985: 33.

Linepithema humilioides (Wilson ): Shattuck 1992a: 16. First combination in Linepithema .

Type material examined

Holotype. Worker. Dominican amber [no further data] ( MCZC).

Worker measurements

Holotype: HL 0.67, HW 0.44, SL 0.74, FL 0.53, LHT 0.62, PW 0.37, OI 1.8, SI 167, CI 66.

Worker description

As given in generic description, but with some characters obscured, including the mandibular dentition and the petiole. Additional details include:

Head in full frontal view longer than broad (CI = 66). Sides of head subparallel and convex, head slightly wider posterior than anterior to compound eyes. Compound eyes of moderate size (OI = 1.8), with about 70 ommatidia, and surpassing lateral margins in full frontal view.

Dorsal surfaces of head, mesosoma, and metasoma devoid of erect setae.

Discussion

This species is known from a single worker specimen, briefly described by Wilson (1985) and placed in the genus Iridomyrmex . At the time, Iridomyrmex had a broad definition encompassing both old world and new world forms. When Shattuck (1992a) redefined Iridomyrmex and moved most of the new world species into Linepithema , he transferred humilioides as well even though humilioides lacks many of the apomorphies that define extant Linepithema . In particular, humilioides does not possess the medially concave anterior clypeal margin of Linepithema , and the eyes of humilioides are located considerably more posterior and lateral on the head than in any of the extant Linepithema species.

The affinity of humilioides with Gracilidris is supported by the position and shape of the eyes, the length of the legs and antennal scapes, the reduced pilosity, and by the shape and forward projection of the clypeus. This combination of characters is unique among the dolichoderines. However, this association should be regarded as tentative. Both humilioides and pombero are in many respects generalized dolichoderine ants, and some of their similarity may be pleisiomorphic. Additionally, many key characters of Gracilidris are not visible in the fossil including, unfortunately, the petiole.