Archimyrmex
| Archimyrmex Temporal range: Middle Eocene | |
|---|---|
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| A. wedmannae holotpe | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Family: | Formicidae |
| Subfamily: | Myrmeciinae |
| Genus: | †Archimyrmex Cockerell, 1923 |
| Species | |
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| Synonyms | |
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Archimyrmex is an extinct genus of ant in the formicid subfamily Myrmeciinae. The genus contains four described species, Archimyrmex rostratus, Archimyrmex piatnitzkii, Archimyrmex smekali and Archimyrmex wedmannae. Archimyrmex is known from a group of Middle Eocene fossils which were found in North America, South America, and Europe.[1]
History and classification
When described the genus Archimyrmex was known from a solitary fossil preserved as an impression in fine shale of the Green River formation in Colorado. The fossil was recovered in July 1922 from the "station 1" fossil site near the top of the Ute trail by Mrs. Cockerell.[2] One side of the A. rostratus holotype is currently deposited in the University of Colorado paleontology collections while the counterpart is in the US National Museum, and an additional eleven fossils were known as of 2002.[3] The holotype was first studied by paleoentomologist Theodore Dru Alison Cockerell of the University of Colorado and his 1923 type description of the new genus and species was published in The Entomologist.[4] The specific epithet "rostratus" is a reference to the beak-like outline of the mandibles seen in the type specimen.[2]
Cockerell placed the genus into the subfamily Ponerinae. He noted similarities between Archimyrmex and Myrmecia and Prionomyrmex, suggesting Archimyrmex to be an intermediate between the two other genera. The genus was re-described in 1928 by paleoentomologist William Wheeler who moved the genus from Ponerinae to Myrmicinae. This placement was not challenged until a 2003 paper by Russian paleoentomologists G.M. Dlussky and K.S. Perfilieva, who moved the genus again, this time to the primitive Subfamily Myrmeciinae based on the close similarity between Archimyrmex and Prionomyrmex.[1][3][5][5] In 1957, an additional species of fossil ant was described from the Middle Eocene Ventana Formation in the Rio Pichileufu region of Argentina by M.J. Viana and J.A. Haedo Rossi. They placed the species into a new genus, "Ameghinoia" as "Ameghinoia" piatnitzkii. As with Archimyrmex, the genus was first placed in Ponerinae. It was subsequently moved to Myrmeciinae by R.R. Snelling in 1981. A second Ventana Formation ant species was described in 1981 by E. Rossi de Garcia and placed into another new genus "Polanskiella" as "P." smekali. Recovered from an outcrop of the Ventana Formation in the Rio Limay area, Rossi de Garcia distinguished the new species from "A." piatnitzkii based on characteristics of the wing venation and because of the difference in size of the two type specimens. A series of fossils from the three genera were examined by Dlussky and Perfilieva and based on the very notable similarities between the three species, they synonymized the three genera under Archimyrmex, treating both "Ameghinoia" and "Polanskiella" as junior synonyms. A fourth species, A. wedmannae was added to the genus in 2012 based on fossils found in the Middle Eocene Messel Pit site of Germany. The specific epithet was chosen by Dlussky.[1]
Description
In general Archimyrmex individuals have a head capsule that bears a set of enlarged mandibles with either a rectangular or triangular outline. The mandibles have a mixed arrangement of teeth and small denticles on the inside margin. The gynes have long legs and long mesosomas, an elongated petiole which is usually smooth in profile on the upper surface. The petiole structure in combination with little to no constriction between abdominal segments III and IV is unique to the genus and separates it from the other Myrmeciinae genera.[1][5]
Females of the type species A. rostratus have a body length estimated to be between 13.2–15.8 mm (0.52–0.62 in), with a small gaster that is shorter than the alitrunk and sporting a short thick sting. The head capsules have antennae borne on a scape which is long and passes the edge of the occipital margin of the head. The short, thickened mandibles have several larger teeth interspersed with small denticles,[5] and are about 50% of the length of the head capsule.[1]
A. piatnitzkii is reported from three specimens, giving a body length between 16–18 mm (0.63–0.71 in). The head capsule is slightly ovoid, being a little longer than it is wide and having mandibles that are notably shorter than the head. As with A. smekali, the alitrunk is massive, being between 1.7-1.8 times as long as it is tall. The legs are like those of the other species, being long and thin. In contrast to the other species, the petiole of A. piatnitzkii has a notable and distinct node and its separated further from A. smekali by the lack of a post-petiole constriction.[5]
The A. smekali lectotype is a female that has an estimated body length of 3 cm (1.2 in) with an alitrunk that is described as "relatively massive" (being only 1.7-1.9 times as long as tall) and an oval shaped gaster. There is a notable constriction in the post-petiole abdominal segment not seen in the other species. The head capsule has mandibles which are about 70% as long as the head capsule,[1] and have four to five large teeth each. The antennal scape is longer than the occipital margin and the antenna is composed of an estimated twelve antennomeres.[5]
A. wedmannae from Germany is described from a single gyne that is approximately 23 mm (0.91 in). The species has a head which is shorter than it is wide, but which has mandibles about as long as the head and which are triangular in outline. As with the three other species the antennal scape is long, one third of the scape length protrudes past the occipital margin of the head. The pronotum in profile is either straight or weakly concave, and the petiole is weakly rounded with no node present. The gaster has a well developed and long sting.[1]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Dlussky, G.M. (2012). "New Fossil Ants of the Subfamily Myrmeciinae (Hymenoptera, Formicidae) from Germany". Paleontological Journal 46 (3): 288–292. doi:10.1134/s0031030111050054.
- ↑ 2.0 2.1 Cockerell, T.D.A. (1923). "The earliest known ponerine ant". The Entomologist 56: 51–52.
- ↑ 3.0 3.1 Dlussky, G.M.; Rasnitsyn, A.P. (2002). "Ants (Hymenoptera: Formicidae) of Formation Green River and some other Middle Eocene deposits of North America". Russian Entomological Journal 11 (4): 411–436.
- ↑ Carpenter, F. M. (1930). "The fossil ants of North America." (PDF). Bulletin of the Museum of Comparative Zoology 70: 1–66.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Dlussky, G.M.; Perfilieva, K.S. (2003). "Paleogene ants of the genus Archimyrmex Cockerell, 1923 (Hymenoptera, Formicidae, Myrmeciinae)" (PDF). Paleontological Journal 37 (1): 39–47.
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