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''Electromyrmex'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
ant Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...
s in the formicid subfamily
Dolichoderinae Dolichoderinae is a subfamily of ants, which includes species such as the Argentine ant (''Linepithema humile''), the erratic ant, the odorous house ant, and the cone ant. The subfamily presents a great diversity of species throughout the wor ...
. The genus contains a single described
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, ''Electromyrmex klebsi'' and is known from a group of
Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s which were found in Europe.


History and classification

''Electromyrmex'' is known from several fossil specimens of adult workers. A worker was first discovered preserved as an
inclusion Inclusion or Include may refer to: Sociology * Social inclusion, action taken to support people of different backgrounds sharing life together. ** Inclusion (disability rights), promotion of people with disabilities sharing various aspects of lif ...
in a transparent chunk of
Baltic amber Baltic amber or succinite is amber from the Baltic region, home of its largest known deposits. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that this forested region provided the re ...
, and additional workers have been identified from Baltic amber found in Lithuania. Workers of an undescribed species labeled as "''Electromyrmex'' sp A" have been found in Bitterfeld amber. Baltic amber is approximately forty six million years old, having been deposited during
Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...
stage of the
Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...
. There is debate on what plant family the amber was produced by, with macrofossil and microfossil evidence suggesting a ''
Pinus A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as c ...
'' relative, while chemical and spectroscopic evidence suggests ''
Agathis ''Agathis'', commonly known as kauri or dammara, is a genus of evergreen coniferous trees, native to Australasia and Southeast Asia. It is one of three extant genera in the family Araucariaceae, alongside ''Wollemia'' and ''Araucaria'' (being ...
'' or ''
Sciadopitys ''Sciadopitys'', commonly called umbrella pines, is a genus of a unique conifers now endemic to Japan. The sole living member of the family Sciadopityaceae is '' Sciadopitys verticillata'', a living fossil. The oldest fossils of ''Sciadopitys'' ...
''. The paleoenvironment of the Eocene Baltic forests where the ''P. eocenicum'' lived was that of humid temperate to subtropical islands. The forests were composed of mostly ''
Quercus An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...
'' and ''Pinus'' species, while the lower sections of the forests had paratropical plant elements, such as palms. The genus and species were first mentioned by entomologist
William Morton Wheeler William Morton Wheeler (March 19, 1865 – April 19, 1937) was an American entomologist, myrmecologist and professor at Harvard University. Biography Early life and education William Morton Wheeler was born on March 19, 1865, to parents Juliu ...
in 1908 and again in 1910. However neither the 1908 or 1910 publications were accompanied by a description of the genus or species, rather they were noted as to be described later. Wheeler published a formal description for ''Electromyrmex'' in his 1915 work ''The ants of the Baltic amber'', seven years after first publishing the name. When first examined and described, the type worker was in the private collection of Professor Richard Klebs of Königsberg University, who first interested Wheeler on working with Baltic amber ant specimens. Sometime after the 1910 type description, the specimen, along with parts of the Klebs collection, was moved to the Georg-August University Geoscientific Center. An additional two fossils in the
University of Rennes 1 The University of Rennes 1 was a public university located in Rennes, France. It was founded in 1970, after splitting of the historic University of Rennes into two universities. On January 1, 2023, the University of Rennes 1 merged with five gra ...
collections have been identified as ''E. klebsi'' workers. Wheeler placed the genus into the
Myrmicinae Myrmicinae is a subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily ...
tribe
Myrmicini Myrmicini is a tribe of ants in the subfamily Myrmicinae. It is not to be confused with the very similar-sounding tribes Myrmecinini (also in subfamily Myrmicinae) and Myrmeciini, which is in the subfamily Myrmeciinae. While the type genus of Myr ...
, and this placement was unchanged until 1988. In a paper discussing the early evolution of ants, the genus was treated as ''
incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
'' in Myrmicinae, with no tribal assignment. Based on the slender nature of the body and appendages, combined with large forward placed eyes, Wheeler suggested an
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
habit similar to the living genera '' Pseudomyrma'' and ''"Sima"'' (now called '' Tetraponera'').


Description

The worker described by Wheeler is estimated to be about . The exoskeleton is a mix of smooth and ridged textures, with longitudinal ridges on the head, petiole and postpetiol, while the mesopleurae and epinotum have transverse ridges. In contrast the gaster,
pronotum The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on e ...
and
mandibles In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
plus clypeus are shining and smooth. The overall coloration of the workers is black, with a silvery luster present on most of the body. The large head is rectangular, narrowing to a prominent concave rear margin. The eyes are large and positioned near the front of the head, while there are no
ocelli A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...
visible on the head. The mandibles are elongated, slightly curved near the bases, and narrow. They are separated into distinct base and masticatory areas, with very small uniform teeth populating the whole length of the chewing edge. The thorax forms a slender neck from the prothorax, on which the head is connected, and the remainder of the thorax is narrower in width than the head. The upper surface of the thorax is divided by a distinct constriction between the
mesonotum The mesothorax is the middle of the three segments of the thorax of hexapods, and bears the second pair of legs. Its principal sclerites (exoskeletal plates) are the mesonotum (dorsal), the mesosternum ( ventral), and the mesopleuron (lateral) ...
and epinotum. Two small spines rise from the rear edge of the epinotum. The petiole is thin with no teeth on the underside and only a slight thickening into a node on the upper surface. The abdominal segment connected to the petiole is modified into a postpetiole that is thicker and a little shorter than the petiole, and which has a distinct convex curve to the upper surface. Of similar size as the head, the gaster has a notably enlarged first segment and in the holotype specimen the remaining abdominal segments are withdrawn into it.


References


External links

* {{Taxonbar, from=Q18102500 Myrmicinae Eocene insects of Europe Fossil taxa described in 1910 Hymenoptera of Europe Baltic amber Monotypic fossil ant genera