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Eotemnothorax
| †Eotemnothorax Temporal range: 37.8–33.9 Ma Priabonian, Late Eocene | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Family: | Formicidae |
| Subfamily: | Myrmicinae |
| Tribe: | Crematogastrini |
| Genus: | †Eotemnothorax Radchenko, 2024 |
| Type species | |
| Leptothorax gracilis, now Eotemnothorax gracilis | |
| Diversity | |
| 18 fossil species (Species Checklist) | |
Identification
Males
Body length ca. 2.5–3.0 mm. Head subglobular, widely rounded above eyes. Eyes and ocelli large. Medial clypeal carina absent. Mandibles elongate-triangular, with a clearly defined masticatory margin with four acute teeth. Maxillary palps 5-segmented, labial palps 3-segmented. Antennae 13-segmented, scape short, funiculus filiform, without apical club; 1st funicular segment short and thick, 2nd segment long and thin, longer than remaining segments, except for apical one. Scutum with well developed, V-shaped notauli. Propodeum gradually rounded, either angulated or with very short blunt denticles (seen in profile). Forewing with closed cells 1+2r and mcu, cell 3r open, rarely closed. Meso- and metatibiae with small simple spur, pretarsal claws simple.
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Workers
Antennae 12-segmented (11-segmented in Eotemnothorax placivus), with distinct 3-segmented apical club. Maxillary palps 5-segmented, labial palps 3-segmented. Clypeus without medial longitudinal carina. Masticatory margin of mandibles with 5–6 teeth and without diastema. Stipes of maxilla without transverse crest. Metanotal groove developed in various degrees, always presents. Propodeal lobes rounded. Meso- and metatibiae of most species without spur, but Eotemnothorax rectispinus, Eotemnothorax groehni, Eotemnothorax rav and Eotemnothorax khomychi have a short simple spur, and Eotemnothorax perkovskii has a longer simple spur. In addition, all known gynes have short simple spur.
In many characters, all studied fossil workers of Eotemnothorax are similar to modern Temnothorax, but they differ in the absence of a medial clypeal carina, which is considered a key diagnostic character of the genus Temnothorax. Additionally, all queens and some workers examined have a distinct simple spur on the meso- and/or metatibiae that are always absent in Temnothorax (Bolton 2003).
Blaimer et al. (2018), based on the molecular phylogenetic analysis, established an informal Formicoxenus genus-group within the tribe Crematogastrini Forel, 1893, including the genera Leptothorax, Harpagoxenus, Formicoxenus (= Leptothorax genus group sensu Prebus 2017, LGG), Temnothorax, Vombisidris and Gauromyrmex. However, the mandibles of workers and gynes of 12 amber ‘Temnothorax’ species (in six species studied the mandible dentition is hidden) have 5–6 teeth on the masticatory margin and are lacking diastema (Figs 3, F; 7, F; 10, F), presence of which is one of the most important characteristics of Vombisidris (Bolton 1991). Gauromyrmex is clearly distinguished from the amber ‘Temnothorax’ by the 2-segmented maxillary and labial palps, 11-segmented antennae, the shape of the head and clypeus, incrassated meso- and metafemora, etc. (Bolton 2003).
Mayr (1868) first described males of Leptothorax gracilis (now Eotemnothorax gracilis) based on two specimens from the same piece of amber. Among the diagnostic charters mentioned by Mayr, the following appear crucial: the antennae are 13-segmented, the funiculus is filiform, without an apical club, the apical segment is the longest, the 1st funicular segment is short and thick, the 2nd segment is long and thin, and the mandibles are subtriangular, with a distinct masticatory margin and four sharp teeth. The examination of further 21 males from all late Eocene European ambers confirmed their similarity with L. gracilis in the main diagnostic features: they have 13-segmen ted antennae with a filiform funiculus without an apical club, a short scape, a short and thick 1st funicular segment, a long and thin 2nd segment, and subtriangular man dibles with a clearly defined masticatory mar gin with four sharp teeth (Fig. 11, A, C, D; Table 3).
Consequently, by the antennal structure they resemble the males of modern species from the Leptothorax genus group, but the latter have 12-segmented antennae and rather narrow and short mandibles with a blunt, edentate masticatory margin. At the same time, the investigated males differ well from modern species of Temnothorax, which have a funiculus with a 3–4-segmented apical club developed to varying degrees, a longer scape, and especially much shorter second and remaining funicular segments (Table 3) (see also Bolton 2003). In conclusion, all males of the amber ‘Temnothorax’ species have a ‘mixture’ of many characters of the modern Temnothorax and LGG genera and cannot be attributed to any of them.
As a result, I decided to establish a new genus – Eotemnothorax for the previously described species of Temnothorax from late Eocene European ambers.
Distribution
This taxon is known from Baltic amber, Baltic Sea region, Europe (Priabonian, Late Eocene), Bitterfeld amber, Baltic Sea region, Europe (Priabonian, Late Eocene), Danish-Scandinavian amber (Priabonian, Late Eocene) and Rovno amber, Baltic Sea region, Europe (Priabonian, Late Eocene).
Castes
Nomenclature
The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.
- †EOTEMNOTHORAX [Myrmicinae: Crematogastrini]
- †Eotemnothorax Radchenko, 2024: 719. Type-species: †Leptothorax gracilis, by original designation.