''Yantaromyrmex'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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 ...

s first described in 2013. Members of this genus are in the 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 ...

of the family Formicidae, known from

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'', "da ...

Early Oligocene The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene Epoch/ Series. It spans the time between . It is preceded by the Priabonian Stage (part of the Eocene) and is followed by the Chattian ...

fossils found in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

. 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 Gustav L. Mayr (12 October 1830 – 14 July 1908) was an Austrian entomologist and professor in Budapest and Vienna. He specialised in Hymenoptera, being particularly known for his studies of ants.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 ...

present.

Distribution

Individuals of ''Yantaromyrmex'' species have been found as inclusions in four different

amber deposits in Europe.

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 ...

is approximately 46 million years old, having been deposited during the

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 ...

stage of the Middle Eocene. There is debate on what plant family the amber was produced by, with evidence supporting them being relatives of either '' Agathis'' or ''

Pseudolarix ''Pseudolarix'' is a genus of coniferous trees in the pine family Pinaceae containing three species, the extant '' Pseudolarix amabilis'' and the extinct species '' Pseudolarix japonica'' and '' Pseudolarix wehrii''. ''Pseudolarix'' species are ...

''.

Rovno amber Rivne amber, occasionally called Ukrainian amber, is amber found in the Rivne Oblast and surrounding regions of Ukraine and Belarus. The amber is dated between Late Eocene and Early Miocene, and suggested to be contemporaneous to Baltic amber. ...

, recovered from deposits in the

Rivne Rivne (; uk, Рівне ),) also known as Rovno (Russian: Ровно; Polish: Równe; Yiddish: ראָוונע), is a city in western Ukraine. The city is the administrative center of Rivne Oblast (province), as well as the surrounding Rivne Raio ...

region of

Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...

, is slightly younger in age, being dated to the

Bartonian The Bartonian is, in the ICS's geologic time scale, a stage or age in the middle Eocene Epoch or Series. The Bartonian Age spans the time between . It is preceded by the Lutetian and is followed by the Priabonian Age. Stratigraphic defini ...

to Priabonian of the

Late 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'', "d ...

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 ...

is recovered from coal deposits in the Saxony area of Germany and the dating of the deposits is uncertain. Bitterfeld represents a section of the Eocene Paratethys Sea, and the amber that is recovered from the region is thought to be redeposited from older sediments. The fossil record of Bitterfeld and Baltic amber insects is very similar with a number of shared species, and that similarity is noted in the suggestions of a single source for the paleoforest that produced the amber. The amber deposits on the Danish coast, often referred to as Scandinavian amber, is of similar age to the other three European ambers, however a study of the ant fauna published in 2009 indicates Scandinavian amber has a fairly distinct ant assemblage. ''Y. constricta'' and ''Y. geinitzi'' are both identified from all four European ambers, while ''Y. samlandicus'' has been described from Baltic, Bitterfeld and Rovno fossils. ''Y. intermedius'' and ''Y. mayrianum'', are each known from only a few fossils, ''Y. intermedius'' from only a single Bitterfeld amber fossil while ''Y. mayrianum'' is known from a Baltic amber and a Rovno amber fossil.

History and classification

The type specimens of ''Y. geinitzi'' and ''Y. constrictus'' were collected in 1868, and when first described were part of the

University of Königsberg The University of Königsberg (german: Albertus-Universität Königsberg) was the university of Königsberg in East Prussia. It was founded in 1544 as the world's second Protestant academy (after the University of Marburg) by Duke Albert of Pruss ...

's amber collection. The fossils were initially studied by Austrian entomologist

Dolichoderus ''Dolichoderus'' is a genus of ants found worldwide. Taxonomy The ants of the Neotropical genus ''Monacis'' were revised in 1959 by Kempf. However, Brown in 1973 and G. C. Wheeler and J. Wheeler in 1973 and 1976 considered both ''Monacis'' and ' ...

''. Mayr's 1868 type descriptions of the new species were published in the journal '' Beiträge zur Naturkunde Preussens''. All the ''Y. samlandicus''

syntype In biological nomenclature, a syntype is any one of two or more biological types that is listed in a description of a taxon where no holotype was designated. Precise definitions of this and related terms for types have been established as part of ...

s were collected by 1915, and the first 73 described were part of the University of Königsberg amber collection. These fossils were first studied by American 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 Wheel ...

, whose type description of ''"Iridomyrmex" samlandica'' was published in the journal ''Schriften der Physikalisch-Ökonomischen Gesellschaft zu Königsberg''. Both ''Y. geinitzi'' and ''Y. constrictus'' were both moved from ''Hypoclinea'' to the small related genus '' Bothriomyrmex'' in 1873 by Dalla Torre. In his 1915 paper ''The ants of Baltic Amber'' Wheeler suggested both species and the newly named ''"I." samlandica'' would be better placed in the genus ''

Iridomyrmex ''Iridomyrmex'' is a genus of ants called rainbow ants (referring to their blue-green iridescent sheen) first described by Austrian entomologist Gustav Mayr in 1862. He placed the genus in the subfamily Dolichoderinae of the family Formici ...

'' and noted ''Y. geinitzi'' to be one of the most abundant ant species in the Baltic amber he had studied. Wheeler based the placement on the structuring of the labial and maxillary palpi. This placement was unchallenged until the genus was reviewed, redefined and split up in 1992 by Steven Shattuck. In his review, ''Iridomyrmex'' was split into a more restricted genus group while the other species which did not match the definition of that genus were moved to other genera. At that time Shattuck provisionally kept ''Y. geinitzi'' in ''Iridomyrmex'' citing a lack of specimens for him to study, while both ''Y. constrictus'' and ''Y. samlandicus'' were transferred to the genus ''

Anonychomyrma ''Anonychomyrma'' is a genus of ants in the subfamily Dolichoderinae. Distribution and habitat The genus is mainly distributed in New Guinea, Solomon Islands and Australia; a single species is known from Malaysia and Indonesia. They nest on th ...

''. The placements of ''Y. geinitzi'' was retained until 2011 when Shattuck and Brian Heterick again reviewed ''Iridomyrmex''. With more fossils to study and based on a number of characters, ''Y. geinitzi'' was also moved to ''Anonychomyrma''. The three species were reviewed again, this time in 2013. The species were examined by Russian entomologists G.M. Dlussky and D.A. Dubovikoff, who they came to the conclusion that the three species, along with two unnamed species, were distinct from ''Anonychomyrma'' and ''Iridomyrmex''. Based on the differences they noted, Dlussky and Dubovikoff erected the new genus ''Yantaromyrmex'' in 2013 for these ants and described two new species, ''Y. intermedius'' and ''Y. mayrinaum''. The name is a combination of the Russian word ', translated as yantar, meaning "amber" and the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

' which means "ant". They noted the new species name ''intermedius'' was derived from the Latin word of that same spelling, meaning "intermediate". They chose the name ''mayrianum'' to honor Gustav Mayr for his work as a myrmecologist.

Description

The genus is characterized by workers which have head-capsules that are trapezoidal in shape, narrowing at the front and widening towards the rear of the capsule. The oval

compound eye A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which disti ...

s are generally placed slightly to the rear of the capsules midpoint, and lacking

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 ...

completely. The mandibles have a number of teeth along the masticatory margin (the middle area of the mandibles) and an overall triangular shape. The gaster has a flat first

tergite A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'mar ...

that does not cover the petiole, a flat fourth abdominal sternite.

''Y. constrictus''

Overall ''Y. constrictus'' can be distinguished from the congeneric ''Y. geinitzi'' in several ways. ''Y. geinitzi'' individuals are overall more gracile in form with a less constricted

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 the

mesosoma The mesosoma is the middle part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the legs, and, in the case of winged insects, the wings. In hymenopterans of ...

has a less convex appearance. ''Y. constrictus'' specimens have maxillary palps (

sensory organs A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...

) which are six-jointed, labial palps which are four jointed, and an abundantly hairy body. The antennae have a scape (the first segment of the antenna) which just passes the back-edge of the head capsule on both female and ergatomorphic (male) workers. The ergatomorphs have larger and more rounded

compound eyes A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distin ...

than the workers, and the antennae are overall longer than in the workers. Both males and workers have a five segmented gaster and the males are distinguished by the slightly protruding stipites (the second segment of the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

) at the tip of segment five.

''Y. geinitzi''

Overall ''Y. geinitzi'' can be distinguished from the related Baltic amber species ''Y. constricta'' in several ways. ''Y. geinitzi'' individuals are overall more gracile in form with a less constricted

and the mesosoma has a less convex appearance. ''Y. geinitzi'' specimens have maxillary palps which are six-jointed, labial palps which are four jointed, and the clypeal border is sinuately indented in the middle. The pupae which Wheeler referred to the species are noted to not have any cocoon unlike the modern larvae of some ant subfamilies which will spin a cocoon to pupate in. The eyes of ''Y. geinitzi'' are placed more to the front and sides of the head capsule than seen in ''Iridomyrmex'' species. Due to the shape of ''Y. geinitzi'', the species may have been a herpetobiont (an inhabitant of the soil's surface), but scientists suggest that these ants inhabited trees, dwelling inside epiphytes and dead plant material (such as branches).

''Y. intermedius''

The only specimen of ''Y. intermedius'' is that has several cracks surrounding it, and areas of white "mold" coatings. The indent behind the

propodeum The propodeum or propodium is the first abdominal segment in Apocrita Hymenoptera (wasps, bees and ants). It is fused with the thorax to form the mesosoma. It is a single large sclerite A sclerite (Greek , ', meaning " hard") is a hardened bod ...

(the first abdominal segment) is deep, the connection between the segment and the thorax is wide and covered in wrinkles of the exoskeleton. The propodeum has an angular appearance with a rounded corner when viewed from the side. This separates the species from both ''Y. geinitzi'' and ''Y. mayrianum''. The legs of ''Y. intermedius'' are generally free of hairs while the mesosoma and head have only a few sparse hairs on the upper surface. This is different than the much hairier ''Y. constrictus'' which always has numerous erect hairs on the body and legs. The high conical propodeum and scape which does not extend to the edge of the head capsule isolate ''Y. intermedius'' from ''Y. samlandicus''. The right antenna of the type specimen is preserved with the head of a '' Ctenobethylus goepperti'' worker ant clamped near the tip, and it seems the two had just fought prior to entombment.

''Y. mayrianum''

Workers of ''Y. mayrianum'' range in length from approximately and look very similar to workers of ''Y. geinitzi''. In both species the indent behind the first abdominal segment is broader and shallower than seen in ''Y. constrictus'', ''Y. samlandicus'' and ''Y. intermedius''. Also unlike the other three species the first abdominal segments surface is smooth and unsculptured. ''Y. mayrianum'' can be distinguished from ''Y. geinitzi'' by the amount of hairs found on the workers body. In ''Y. mayrianum'' there is abundant erect hair covering the entire body, on the underside head capsule and along the eye margins and leg undersides. In contrast ''Y. geinitzi'' workers have smooth eye margins and legs, and a sparse scattering of hairs on the mesosoma, last segments of the abdomen and along the upper side of the head.

''Y. samlandicus''

''Y. samlandicus'' specimens have maxillary palps which are six jointed, labial palps which are four jointed, and a total body length between . The antennae each possess twelve segments and a scape that curves at the base. The thorax is narrower in profile than the head capsule, reaching its widest in the broad flattened

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 ...

. The petiole is notably broad and short, having a high node that has a rounded point on the upper side. ''Y. samlandicus'' specimens have fine to coarse punctuation (small spots) across the head and thorax and an overall coloration that is black, though some specimens have a reddish tone to the legs or antennae.

References

{{Taxonbar, from=Q18926228 Oligocene insects Eocene insects Prehistoric insects of Europe Fossil taxa described in 1868 Fossil taxa described in 1873 Fossil taxa described in 1915 Fossil taxa described in 1992 Fossil taxa described in 2011 Fossil taxa described in 2013 † Fossil ant genera Baltic amber Priabonian genus first appearances Chattian genus extinctions Rovno amber