Gracilidris humiloides

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Gracilidris humiloides
Temporal range: Burdigalian, Early Miocene
Dominican amber, Dominican Republic
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Dolichoderinae
Genus: Gracilidris
Species: G. humiloides
Binomial name
Gracilidris humiloides
(Wilson, 1985)

Known from a single Dominican amber worker.

Identification

Distribution

This taxon was described from Dominican amber, Dominican Republic (Burdigalian, Early Miocene).

Castes

Known only from the worker caste.

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • humiloides. †Iridomyrmex humiloides Wilson, 1985c: 33, fig. 11 (w.) DOMINICAN AMBER (Miocene). Combination in Linepithema: Shattuck, 1992a: 16; in Gracilidris: Wild & Cuezzo, 2006: 66.

Holotype: Museum of Comparative Zoology, without number. Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Wild & Cuezzo (2006) - 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.

Description

Worker

Wild & Cuezzo (2006) - 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.

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.

References