Archimyrmex is an extinct genus of ant in the formicid subfamily Myrmeciinae, described by palaeoentomologist Theodore Cockerell in 1923. The genus contains four described species, Archimyrmex rostratus, Archimyrmex piatnitzkyi, 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. The genus was initially placed in the subfamily Ponerinae, but it was later placed in Myrmeciinae; it is now believed to be the ancestor of the extant primitive genus Myrmecia from Australia. Despite this, Archimyrmex is not a member to any tribe and is regarded as incertae sedis within Myrmeciinae. However, some authors believe Archimyrmex should be assigned as incertae sedis within Formicidae. These ants can be characterised by their large mandibles and body length, ranging from 13.2 to 30 mm (0.52 to 1.18 in). They also have long, thin legs and an elongated mesosoma (thorax) and petiole.
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 entomologist Wilmatte Porter Cockerell.[1] 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.[2] The holotype was first studied by palaeoentomologist 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.[3] The specific epithet "rostratus" is a reference to the beak-like outline of the mandibles seen in the type specimen.[1]
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 palaeoentomologist William Wheeler who moved the genus from Ponerinae to Myrmicinae. This placement was not challenged until a 2003 paper by Russian palaeoentomologists 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.[2][4][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" piatnitzkyi. 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." piatnitzkyi 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 described by Dlussky in 2012 based on fossils found in the Middle Eocene Messel Pit site of Germany. The specific epithet was chosen by Dlussky to honour paleoentomologist Sonja Wedmann.[4]