Prionomyrmex is an extinct genus of bulldog ants in the subfamily Myrmeciinae of the family Formicidae. It was first described by Gustav Mayr in 1868, after he collected a holotype worker of P. longiceps in Baltic amber. Three species are currently described, characterised by their long mandibles, slender bodies and large size. These ants are known from the Eocene and Late Oligocene, with fossil specimens only found around Europe. It is suggested that these ants preferred to live in jungles, with one species assumed to be an arboreal nesting species. These ants had a powerful stinger that was used to subdue prey. In 2000, it was suggested by Cesare Baroni Urbani that the living species Nothomyrmecia macrops and a species he described both belonged to Prionomyrmex, but this proposal has not been widely accepted by the entomological community. Instead, scientists still classify the two genera distinctive from each other, making Nothomyrmecia a valid genus.
Discovery and classification
The holotype worker for P. longiceps was collected by Austrian entomologist Gustav Mayr in 1868. The fossil, which was preserved in Baltic amber from the Eocene, was formally described in Mayr's journal article Die Ameisen des baltischen Bernsteins, designating it as the type species by monotypy (the condition of a taxonomic group having only a single taxon described) for the newly established genus Prionomyrmex. Originally, the genus was placed in the subfamily Ponerinae by Mayr, but in 1877, Italian entomologist Carlo Emery classified the genus into the subfamily Myrmeciidae (now known as Myrmeciinae), the same year Emery established the subfamily. In 1915, the tribe Prionomyrmecini was erected by American entomologist William Morton Wheeler, who had placed Prionomyrmex in it. In that year, Wheeler placed the genus back into Ponerinae without any means of justifying his decision. British myrmecologist Horace Donisthorpe would also retain the genus in Ponerinae without explanation, but William Brown Jr. would return it to Myrmeciinae in 1954.
In 2000, Baroni Urbani described a new Baltic fossil species, of which he named it Prionomyrmex janzeni. After examining specimens of the new species and Nothomyrmecia macrops, Baroni Urbani stated that the newly described species and Nothomyrmecia macrops belong to the same genus (Prionomyrmex), in which he synonymised Nothomyrmecia as a genus and treated the tribe Prionomyrmecini as a subfamily, known as Prionomyrmecinae. Prior to this, John S. Clark, the original author who described Nothomyrmecia, noted that the genus was similar in appearance to Prionomyrmex; both the heads and mandibles were identical, but the nodes were different. As the mandibles of Prionomyrmex are similar to that of Nothomyrmecia, this suggests that they are intermediate to each other. This classification was short-lived, as Nothomyrmecia was separated and treated as a valid genus from Prionomyrmex by Dlussky & Perfilieva in 2003, on the base of the fusion of an abdominal segment. Other studies published in the same year came to the same conclusions of Dlussky & Perfilieva, and the subfamily Prionomyrmecinae would later be treated as a tribe in Myrmeciinae. However, Baroni Urbani would treat the tribe as a subfamily again in both his 2005 and 2008 publications, suggesting additional evidence in favor of his former interpretation as opposed to that of Ward and Brady's arguments. In 2012, P. wappleri was described by Gennady M. Dlussky, based on a fossilised worker from the Late Oligocene, Aquitanian stage. This subsequent report that described new fossil myrmecines accepted the classification of Archibald et al. and Ward & Brady without comment on the views of Baroni Urbani.
The generic name is a combination of two words; priono derives from Greek word priōn, meaning "a saw", and myrmex, another Greek word, means "ant".
The following cladogram generated by Archibald and colleagues shows the possible phylogenetic position of Prionomyrmex among some ants of the subfamily Myrmeciinae; note that P. wappleri is absent, as the generated cladogram below was created in 2006 while the species itself was described in 2012.
Description
The genus is characterised by large, slender workers with elongated mandibles, which are narrow and triangular in shape. The mesosoma and appendages are also long. These ants are similar in appearance to Nothomyrmecia, but can be distinguished from the shape of their node. They also had a powerful sting located in the abdomen. Two of the three species are from the Eocene while the third species is from the Late Oligocene.