Incertogaster primitiva

†Incertogaster primitiva; Temporal range: Priabonian, Late Eocene K Pa Eo Ol Mi Pl Rovno amber, Ukraine
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Genus:	Incertogaster
Species:	†I. primitiva
Binomial name
	†Incertogaster primitiva; (Radchenko & Dlussky, 2019)

Boudinot et al. (2024), Note 3 - The amber-preserved males described by Emery as †Crematogaster praecursor and Radchenko & Dlussky as †Crematogaster primitiva are unlikely to be representatives of either the stem or crown of the genus Crematogaster and are incertae sedis in the Myrmicinae within †Incertogaster. Both specimens have 13-merous antennae, while all Crematogaster males examined by the lead author have antennae that are 10–12-merous (Bolton 2003, p. 286; BEB, unpubl. data). Other diagnostic features include the short scape, which is ≤ 2 × the length of the pedicel, the pedicel shape, which is globular rather than cylindrical, and the mandibles, which are reduced or otherwise vestigial; the anterodorsal position of the postpetiolar helcium on abdominal segment IV can be difficult to discern. Unfortunately, Emery did not illustrate the wings or the face of †I. praecursor, so the fossil may need to be considered unidentifiable, hence subjectively invalid, if the specimen does not resurface. †Incertogaster primitiva, on the other hand, is well illustrated; its scapes are about 4 × the length of the pedicels, and the pedicels are not swollen or globular in shape. The mesosoma of this fossil (PMJ Pa 5824) is large and the mesoscutum is impressed, as in many Crematogaster, but the long and strongly nodiform petiole also contradict placement in that genus. At present, we cannot confidently attribute †I. primitiva to any valid generic taxon.

Identification

Radchenko and Dlussky (2019) - Based on the structure of the waist, mesosoma and head, as well as on the character of the forewing venation, we have no doubt that I. primitiva belongs to the genus Crematogaster. Nevertheless, it well differs from all known males of the extant Crematogaster species by its 13-segmented antennae and by its much longer antennal scape that is subequal to the total length of the 1st to 3rd funicular segments (vs. modern species, where antennae are 11- or 12-segmented and the scape length is subequal to the total length of only the 1st and 2nd segments).

With the 13 segment antenna, I. primitiva resembles the fossil Incertogaster praecursor described from the Sicilian amber (Early Oligocene, Rupelian stage, 27.8–34.9 Ma), but differs from that species by its distinctly longer antennal scape and by some details of the forewing venation.

Distribution

This taxon was described from Rovno amber, Baltic Sea region, Europe (Priabonian, Late Eocene).

Biology

Castes

Only known from the male caste.

Male

Radchenko and Dlussky (2019) Figure 2. Line drawings made on original photo of Crematogaster primitiva holotype male. 1 – body in lateral view; 2 – forewing.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

†primitiva. Crematogaster primitiva Radchenko & Dlussky, 2019: 418, figs. 1-2 (m). ROVNO AMBER (Ukraine, Eocene).
- Combination in †Incertogaster: Boudinot, Bock, et al. 2024: 148.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Male

SL 0.32, ML 1.04, MH 0.77, PL 0.32, PH 0.21, PPL 0.16, PPH 0.15, HTL 0.67, total length 3.4 mm. Ratios. ML/MH 1.34, PL/PH 1.54, PPL/PPH 1.09.

Total length ca. 3.4 mm. Head in the specimen is deformed during fossilization (flattened dorso-ventrally) but definitely small. Eyes quite big, situated approximately at midlength of sides of head. Ocelli well developed though not big. Antennae 13-segmented, without defined club, scape relatively long, subequal to total length of 1st to 3rd funicular segments. Mandibles elongate-triangular, with quite narrow but distinct masticatory margin, with is with three small acute teeth.

Mesosoma relatively high, ca. 1.3 times longer than height, scutum high, slightly convex, without Mayrian furrows. Propodeum widely rounded (seen in profile), its dorsal surface ca. 3 times shorter than posterior one. Petiole with short peduncle and massive, quite high node, its dorsum long, convex, declined anteriorly. Postpetiole small, articulated on dorsal surface of first gastral segment. Middle and hind tibiae with simple spur, pretarsal claws simple.

Forewing with closed cells 1r+2r and mcu, cell 3r open distally, cell rm is absent. Cell 1r+2r big, hexagonal, more than twice longer than width; cell mcu trapezoid (not pentagonal), ca. 1.5 times longer than width, reaching distally level of pterostigmal base. Cross-vein cu-a merging with vein section 1M+Cu far proximally than cell mcu (vein section 2M+Cu much longer than cross-vein cu-a).

Body seems smooth and shiny (sculpture on head obscured). Whole body with not abundant, quite long suberect hairs; scape with sparse decumbent pubescence; coxae, inner margins of trochanters and femora with not abundant, long erect to suberect hairs; both inner and outer margins of tibiae and tarsi with short suberect to subdecumbent hairs.

Type Material

Holotype male, Rovno amber, Late Eocene, No. K-25850 (SIZK), AntWeb CASENT No. 17566. Pugach quarry, Klesov deposit, Rovno Region, Ukraine.

Etymology

From the Latin word primitiva(feminine gender) – primitive, that means the primitive structure of the antennae compare to modern species.

References