Usomyrma

Usomyrma; Temporal range: Late Eocene PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Holotype male in profile view
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Dolichoderinae
Tribe:	incertae sedis
Genus:	† Usomyrma ; Dlussky, Radchenko & Dubovikoff, 2014
Species:	†U. mirabilis
Binomial name
	†Usomyrma mirabilis; Dlussky, Radchenko & Dubovikoff, 2014

Last updated October 15, 2023

Usomyrma is an extinct genus of ant in the formicid subfamily Dolichoderinae. The genus contains a single described species, Usomyrma mirabilis, that is known from two Middle Eocene fossils which were found in Scandinavian amber in Denmark.

History

Usomyrma mirabilis is known from two isolated fossils, the holotype and paratype, both of which were housed in the collections of the Zoological Museum of the University of Copenhagen. The fossils are of two complete adult males which have been preserved as inclusions in transparent chunks of Scandinavian amber, also known as Danish amber, found in Denmark.^[1] Scandinavian amber is thought to be similar in age to Baltic, Bitterfeld and Rovno ambers, being approximately late Eocene in age. The four amber faunas have been shown to share 17 ant species in common, which make up over 80% of the specimens in amber collections studied for a 2009 paper. Though a large portion of specimens from Scandinavian amber are of species found in the other ambers, the overall fauna found is notably different from the other three. About twenty-four genera with thirty-five species of ants have been identified as inclusions in Scandinavian amber.^[2]

The fossils were first studied by paleoentomologists Gennady M. Dlussky of the Moscow State University, Alexander Radchenko of the Polish Academy of Sciences and Dmitry Dubovikoff of the Saint Petersburg State University. Their 2014 type description of the new genus and species was published in the journal Acta Palaeontologica Polonica . They coined the genus name as a combination of the Russian Us meaning "mustache" and often used vernacularly in Russia to mean insect antennae, plus myrmecos which is Greek for "ant". The combination was in recognition of the distinct structuring of the antennae on the males. The specific epithet is from the Latin word mirabilis which translates as "wonderful, marvellous, or miraculous", a nod to the unique morphology of the species.^[1]

Classification and taxonomy

Based on interpretation of the wing venation in the U. mirabilis, Dlussky et al suggested the genus was a member of the Dolichoderinae tribe Leptomyrmecini along with the living Leptomyrmex "spider ants"^[3] and the Sicilian amber genus Leptomyrmula . They noted that an unsubscribed male Leptomyrmex male in Dominican amber was distinct enough from the Dominican amber species Leptomyrmex neotropicus to possibly warrant being placed into a new genus, but a full description of the male had not taken place as of 2014. Dlussky et al thought U. mirabilis represented an ancestral wing venation for the tribe, with a progression in vein reduction being present in Leptomyrmula. The Leptomyrmex was treated as a descendant genus of the ancestral form Usomyrma in the classification suggested by Dlussky et al.^[1]

A 2016 study showed the central cell reduction, on which placement of the genus was based, was shown to be derived several times in the subfamily and not specific to the tribe Leptomyrmecini. The study included the description of the species Leptomyrmex relictus from Brazil, and study of the micro-Leptomyrmex clade species. While the macro-Leptomyrmex species have a very reduced wing venation, the micro-Leptomyrmex clade is nested inside the macro species but have retained much of the vein structure unlike the macro-species.^[3] This mosaic of both retained wing venation and reduced wing venation within Leptomyrmex contradicted the gradual vein loss hypothesis that was proposed for an evolutionary grade of Usomyrma - Leptomyrmula - Leptomyrmex. As such both Usomyrma and Leptomyrmula were moved to being placed in Dolichoderinae without tribal placement.^[3]

Description

The described males are approximately 3.5 mm (0.14 in) with a slender profile and elongated appendages. The head is rectangular in outline, being slightly longer than wide, with a straight rear margin and rounded rear edges. Behind the compound eyes, the temples are long with an elevated occiput sporting three large ocelli. Each of the two compound eyes are big, being 0.6 of the head length, with a reniform outline, the concave side of the eye along the front sides. The clypeus is distinct in outline, being elongated with the middle swollen to form an almost triangular bump pointing forward and the rear section of the clypeus is retangular and flattened. Each of the mandibles are triangular and long with a dentate chewing edge that is long and curved showing a pointed apical tooth and at least smaller teeth. Below the crossed mandible tips are the six segmented maxillary palps and the four segmented labial palps. The antennae are elongated with 13 segments, the second funicular segment being distinctly elongate and curved. The fore-wings show a well developed pterostigma and venation that forms several fully closed cells.^[1]

Related Research Articles

Dolichoderinae is a subfamily of ants, which includes species such as the Argentine ant, the erratic ant, the odorous house ant, and the cone ant. The subfamily presents a great diversity of species throughout the world, distributed in different biogeographic realms, from the Palearctic, Nearctic, Afrotropical region and Malaysia, to the Middle East, Australian, and Neotropical regions.

Leptomyrmex, or spider ants, is a genus of ants and a distinctive member of the ant subfamily Dolichoderinae. Commonly known as "spider ants" for their long legs and spider-like movements, these orange and black ants are prominent residents of intact wet forest and sclerophyll habitats throughout their range. One extant species, Leptomyrmex relictus, is known from central Brazil; otherwise, the global distribution of this genus is restricted to eastern Australia, New Caledonia and New Guinea, as well as the nearby Indonesian islands of Aru and Seram.

Sphecomyrma is an extinct genus of ants which existed in the Cretaceous approximately 79 to 92 million years ago. The first specimens were collected in 1966, found embedded in amber which had been exposed in the cliffs of Cliffwood, New Jersey, by Edmund Frey and his wife. In 1967, zoologists E. O. Wilson, Frank Carpenter and William L. Brown, Jr. published a paper describing and naming Sphecomyrma freyi. They described an ant with a mosaic of features—a mix of characteristics from modern ants and aculeate wasps. It possessed a metapleural gland, a feature unique to ants. Furthermore, it was wingless and had a petiole which was ant-like in form. The mandibles were short and wasp-like with only two teeth, the gaster was constricted, and the middle and hind legs had double tibial spurs. The antennae were, in form, midway between the wasps and ants, having a short first segment but a long flexible funiculus. Two additional species, S. canadensis and S. mesaki, were described in 1985 and 2005, respectively.

Burmomyrma is an extinct genus of aculeate hymenopteran, suggested to be an ant. The genus contains a single described species, Burmomyrma rossi. Burmomyrma is known from a single Middle Cretaceous fossil which was found in Asia.

Pristomyrmex rasnitsyni is an extinct species of ant in the genus Pristomyrmex. The species is known from a single Late Eocene fossil which was found in Europe.

Emplastus is an extinct morphogenus of ants in the subfamily Dolichoderinae, known from fossils found in Asia and Europe. The genus contains twelve species described from sites in England, Eastern Europe and Far Eastern Russia.

Yantaromyrmex is an extinct genus of ants first described in 2013. Members of this genus are in the subfamily Dolichoderinae of the family Formicidae, known from Middle Eocene to Early Oligocene fossils found in Europe. The genus currently contains five described species, Y. constrictus, Y. geinitzi, Y. intermedius, Y. mayrianum and Y. samlandicus. The first specimens were collected in 1868 and studied by Austrian entomologist Gustav Mayr, who originally placed the fossils in other ant genera until the fossils were reviewed and subsequently placed into their own genus. These ants are small, measuring from 4 to 6 mm in length and can be characterized by their trapezoidal shaped head-capsules and oval compound eyes that are located slightly to the rear of the capsules midpoint, with no known ocelli present.

Zherichinius is an extinct genus of ants in the subfamily Dolichoderinae known from fossils found in amber from the Middle Eocene of Sakhalin island Far eastern Russia and Bitterfeld, Germany. At the time of description the species Zherichinius horribilis and Zherichinius rapax were two of eight ant species known from Sakhalin fossils.

Protopone is an extinct genus of ants in the formicid subfamily Ponerinae described from fossils found in Europe and Asia. There are seven described species placed into the genus, Protopone? dubia, Protopone germanica, Protopone magna, Protopone oculata, Protopone primigena, Protopone sepulta, and Protopone vetula. Protopone is one several Lutetian Ponerinae genera.

Cyrtopone is an extinct genus of ants in the formicid subfamily Ponerinae described from fossils found in Europe. There are four described species placed into the genus, Cyrtopone curiosa, Cyrtopone elongata, Cyrtopone microcephala, and Cyrtopone striata. Cyrtopone is one several Lutetian Ponerinae genera.

Gerontoformica is an extinct genus of stem-group ants. The genus contains thirteen described species known from Late Cretaceous fossils found in Asia and Europe. The species were described between 2004 and 2016, with a number of the species formerly being placed into the junior synonym genus Sphecomyrmodes.

Camelomecia is an extinct genus of stem-group ants not placed into any Formicidae subfamily. Fossils of the single known species, Camelomecia janovitzi, are known from the Middle Cretaceous of Asia. The genus is one of several ants described from Middle Cretaceous ambers of Myanmar.

Paraneuretus is an extinct genus of formicid in the ant subfamily Aneuretinae known from fossils found in Asia and Europe. The genus contains three middle to late Eocene age species, Paraneuretus dubovikoffi, Paraneuretus longicornis, and Paraneuretus tornquisti.

Baikuris is an extinct genus of ant in the Formicidae subfamily Sphecomyrminae, and is currently placed in the tribe Sphecomyrmini. The genus contains four described species: the type species Baikuris mandibularis, along with Baikuris casei, Baikuris maximus, and Baikuris mirabilis.

Aneuretellus is an extinct genus of ant in the formicid subfamily Aneuretinae, and is one of eight genera of the subfamily. The genus contains a single described species Aneuretellus deformis and is known from one Middle Eocene fossil which was found in Sakhalin in the Russian Far East.

Bradoponera is an extinct genus of ant in the Formicidae subfamily Proceratiinae, and is one of four genera of the subfamily. The genus contains four described species Bradoponera electrina, Bradoponera meieri, Bradoponera similis, and Bradoponera wunderlichi. The species are known from several Middle Eocene amber fossils which were found in Europe.

Aphaenogaster dlusskyana is an extinct species of ant in the subfamily Myrmicinae known from a single Middle Eocene fossil found in amber on Sakhalin. At the time of description A. dlusskyana was one of eight ant species known from Sakhalin fossil.

Electromyrmex is an extinct genus of ants in the formicid subfamily Dolichoderinae. The genus contains a single described species, Electromyrmex klebsi and is known from a group of Middle Eocene fossils which were found in Europe.

Nylanderia pygmaea is an extinct species of formicid in the ant subfamily Formicinae known from fossils found in the Baltic region.

Boltonimecia is an extinct genus of ant in the formicid subfamily Zigrasimeciinae. The genus contains a single described species, Boltonimecia canadensis, and is known from a single Late Cretaceous fossil which was found in Canada. The type species was originally described as a species of the extinct genus Sphecomyrma under the combination Sphecomyrma canadensis.

References

1 2 3 4 Dlussky, G.; Radchenko, A.; Dubovikoff, D. (2014). "A new enigmatic ant genus from late Eocene Danish Amber and its evolutionary and zoogeographic significance". Acta Palaeontologica Polonica. 59 (4): 931–939. doi: 10.4202/app.2012.0028 .
↑ Dlussky, G. M.; Rasnitsyn, A. P. (2009). "Ants (Insecta: Vespida: Formicidae) in the Upper Eocene Amber of Central and Eastern Europe" (PDF). Paleontological Journal. 43 (9): 1024–1042. doi:10.1134/S0031030109090056. S2CID 84191149.
1 2 3 Boudinot, B. E.; Probst, R. S.; Brandao, C. R. F.; Feitosa, R. M.; Ward, P. S. (2016). "Out of the Neotropics: newly discovered relictual species sheds light on the biogeographical history of spider ants (Leptomyrmex, Dolichoderinae, Formicidae)" (PDF). Systematic Entomology. 41 (3): 667–671. doi: 10.1111/syen.12181 .

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[Dlussky2014-1] 1 2 3 4 Dlussky, G.; Radchenko, A.; Dubovikoff, D. (2014). "A new enigmatic ant genus from late Eocene Danish Amber and its evolutionary and zoogeographic significance". Acta Palaeontologica Polonica. 59 (4): 931–939. doi: 10.4202/app.2012.0028 .

[Dlussky2009-2] Dlussky, G. M.; Rasnitsyn, A. P. (2009). "Ants (Insecta: Vespida: Formicidae) in the Upper Eocene Amber of Central and Eastern Europe" (PDF). Paleontological Journal. 43 (9): 1024–1042. doi:10.1134/S0031030109090056. S2CID 84191149.

[Boudinot2016-3] 1 2 3 Boudinot, B. E.; Probst, R. S.; Brandao, C. R. F.; Feitosa, R. M.; Ward, P. S. (2016). "Out of the Neotropics: newly discovered relictual species sheds light on the biogeographical history of spider ants (Leptomyrmex, Dolichoderinae, Formicidae)" (PDF). Systematic Entomology. 41 (3): 667–671. doi: 10.1111/syen.12181 .

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