Sussudio boreus

†Sussudio boreus Temporal range: Bartonian, Middle to Late Eocene K Pa Eo Ol Mi Pl Baltic amber, Baltic Sea region
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Formicinae
Genus:	†Sussudio
Species:	†S. boreus
Binomial name
†Sussudio boreus (Wheeler, W.M., 1915)

A fossil ant from the Baltic amber.

Identification

Definition (worker) (Boudinot et al., 2022).

1. With characters of the Formicinae (see Boudinot et al. (2022), Note 1).
2. Cranium size variable, width somewhat broader than to about twice that of mesosoma (see Boudinot et al. (2022), Note 2).
3. Mandible triangular, with 7–8 teeth.
4. Dorsal mandibular groove extending along lateral mandibular margin in dorsal view.
5. Palps reduced, not reaching midlength of postgenal bridge.
6. Frontal carinae raised above antennal toruli.
7. Antennal toruli abutting posterior clypeal margin.
8. Antennomere count unknown (see Boudinot et al. (2022), Note 3).
9. Antennomere III longer than broad.
10. Compound eyes situated posterior to head midlength.
11. Compound eyes not enormous and long axes subparallel.
12. Ocelli minutely present or absent.
13. Promesonotum domed, raised well above propodeum.
14. Metanotal groove well-developed.
15. Petiolar foramen in profile view clearly raised and margined with conspicuous thickened carina or lip.
16. Petiolar node squamiform, tall; dorsoventral height equal to or possibly exceeding dorsum of propodeum.
17. Abdominal segment III without raised tergosternal fusion.

†Sussudio boreus (the only known species within this genus) was previously placed in the Lasiini (Emery, 1925, Dlussky & Fedoseeva 1988, Bolton, 1994), and has been considered to be a member of the genus Pseudolasius (Wheeler, 1915; LaPolla & Dlussky, 2010). Based on an examination of a syntype (GZG-BST04646) and a nontype (NHMW1984-31-211) worker, as well as the original description from Wheeler (1915), we reject both placements. Neither specimen can be mistaken due to the unique combination of characters they display, including setation, high petiolar nodes, massive crania, and mesosomal form. †Sussudio boreus does not display the modifications of the third abdominal segment characteristic of the Prenolepis genus group, also rejecting its original placement in Pseudolasius (see diagnostic Note 2 above). †Sussudio is excluded from the Lasiini overall by two additional characters: (i) The petiolar node, which is completely vertical and very tall dorsoventrally, is as tall as or possibly taller than the propodeum; and (ii) the raised and conspicuously lipped petiolar foramen. No lasiine, extant or extinct, has such a tall petiolar node, nor do any species display the petiolar foramen conformation observed in †Sussudio.

We cannot confidently place †Sussudio in any extant tribe, therefore, we consider †Sussudio incertae sedis in the Formicinae. As with other fossil taxa, which are of uncertain placement in the Formicinae, micro-CT scanning could be used to evaluate the form of the helcium and third abdominal sternum.

Distribution

This taxon was described from Baltic amber (Bartonian, Middle to Late Eocene) and is also known from Bitterfeld amber (Bartonian, Middle to Late Eocene) and Rovno amber (Priabonian, Late Eocene) (Perkovsky, 2016).

Nomenclature

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

• †boreus. †Pseudolasius boreus Wheeler, W.M. 1915h: 133, fig. 64 (s.w.) BALTIC AMBER (Eocene).
  • See also: LaPolla & Dlussky, 2010: 270.
  • Combination in Sussudio: Boudinot et al., 2022: 143.

References

• Boudinot, B.E., Borowiec, M.L., Prebus, M.M. 2022. Phylogeny, evolution, and classification of the ant genus Lasius, the tribe Lasiini and the subfamily Formicinae (Hymenoptera: Formicidae). Systematic Entomology 47, 113-151 (doi:10.1111/syen.12522).
• LaPolla, J.S. & Dlussky, G.M. 2010. Review of fossil Prenolepis genus-group species. Proceedings of the Entomological Society of Washington 112: 258-273.
• Perkovsky, E.E. 2016. Tropical and Holoarctic ants in late Eocene ambers. Vestnik zoologii 50(2): 111–122 (doi:10.1515/vzoo-2016-0014).
• Wheeler, W.M. 1915i. The ants of the Baltic Amber. Schriften der Physikalisch-Ökonomischen Gesellschaft zu Königsberg 55: 1-142. (page 133, fig. 64 soldier, worker described)