''Electromyrmex'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...

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 world ...

. The genus contains a single described

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, ''Electromyrmex klebsi'' and is known from a group of

Middle Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "dawn ...

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 preserved ...

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, aims to create an environment that supports equal opportunity for individuals and groups that form a society. ** Inclusion (disability rights), promotion of people with disabiliti ...

in a transparent chunk of

Baltic amber The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that these forests created more than 1 ...

, 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 The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that these forests created more than 1 ...

. Baltic amber is approximately forty six million years old, having been deposited during

Lutetian The Lutetian is, in the geologic timescale, a stage or 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 is sometimes referred to as the Midd ...

stage of the

. 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. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accep ...

'' relative, while chemical and spectroscopic evidence suggests ''

Agathis ''Agathis'', commonly known as kauri or dammara, is a genus of 22 species of evergreen tree. The genus is part of the ancient conifer family Araucariaceae, a group once widespread during the Jurassic and Cretaceous periods, but now largely re ...

'' or ''

Sciadopitys ''Sciadopitys verticillata'', the or Japanese umbrella-pine, is a unique conifer endemic to Japan. It is the sole member of the family Sciadopityaceae and genus ''Sciadopitys'', a living fossil with no close relatives. The oldest fossils of ''S ...

''. 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 tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably '' ...

'' 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 Harvard professor. Biography Early life and education William Morton Wheeler was born on March 19, 1865, to parents Julius Morton Wheeler ...

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 Königsberg (, ) was the historic Prussian city that is now Kaliningrad, Russia. Königsberg was founded in 1255 on the site of the ancient Old Prussian settlement ''Twangste'' by the Teutonic Knights during the Northern Crusades, and was named ...

, 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 is a public university located in the city of Rennes, France. It is under the Academy of Rennes. It specializes in science, technology, law, economics, management and philosophy. There are currently about students en ...

collections have been identified as ''E. klebsi'' workers. Wheeler placed the genus into the

Myrmicinae Myrmicinae is a subfamily of ants, with about 140 extant genera; their distribution is cosmopolitan. The pupae lack cocoons. Some species retain a functional sting. The petioles of Myrmicinae consist of two nodes. The nests are permanent and ...

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 ''problematica'' is a term used for a 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 Animal locomotion, 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, but others are exclusively arboreal. Th ...

habit similar to the living genera '' Pseudomyrma'' and ''"Sima"'' (now called ''

Tetraponera ''Tetraponera'' is a genus of ants in the subfamily Pseudomyrmecinae that are commonly known as slender ants and are characterized by their arboreal nature and slender bodies. The 96 described species of ''Tetraponera'' all of which live in holl ...

'').

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 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) on ...

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 ea ...

and

mandibles In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

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 (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...

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) on ...

and

. 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 Fossil taxa described in 1910 Prehistoric insects of Europe Hymenoptera of Europe Baltic amber Fossil ant taxa