''Metanephrocerus'' 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 ...

of big-headed flies in the dipteran subfamily Protonephrocerinae, for which it is one of only two genera. The genus contains four 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 ...

, ''Metanephrocerus belgardeae'', ''M. collini'', ''M. groehni'', and ''M. hoffeinsorum''. ''Metanephrocerus'' 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'', "da ...

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 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 ...

and a single early Eocene fossil from North America.

History and classification

When first described, ''Metanephrocerus'' was known only from two separate fossils, the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

female, and the female

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

were fossilized as inclusions in transparent chunks 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 ...

. Baltic amber is approximately forty-six 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

. There is debate on what plant family produced the amber, with evidence supporting relatives of either an '' Agathis'' or a ''

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 ...

'' relative. Fossils of the type species, ''M. collini'', were first studied by American entomologist Frank M. Carpenter and F. M. Hull who placed the new species in the fossil genus '' Protonephrocerus''. Carpenter and Hull's 1939

type description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

of the new species was published in the monograph series '' Bernstein-Forschungens''. The species was moved to the new genus ''Metanephrocerus'' in a 1948 paper by Martin L Aczél, and since that time both the type specimens have been lost and are considered possibly destroyed. After the ''M. collini'' description, 75 years passed before an additional three related species were described. Two of those, ''M. groehni'' and ''M. hoffeinsorum''. were described from solitary fossil inclusions in Baltic amber. The 2014 descriptions were made by Christian Kehlmaier, Manuel Dierick and Jeffrey H. Skevington, based on detailed CT scans of the specimens. They chose the

species name In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

"groehni" is a patronym honoring Carsten Gröhn, who supported the research of the authors, and who was the owner of the specimen before description. The fossil was to be deposited into the collections of the Geologisch-Paläontologisches Institut und Museum der Universität Hamburg Similarly, the epithet of the second species "hoffeinsorum" is a patronym for Christel and Hans-Werner Hoffeins for the donation of the type fossil to the Senckenberg Deutsches Entomologisches Institut and for their support of the authors research. The third related species, ''M. belgardeae'', bringing the total to four, was described from a compression fossil found in the early Eocene,

Ypresian In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian ...

Klondike Mountain Formation lagerstätten, its discovery expanding both the temporal range and geographic range. ''M. belgardeae'' was described by S. Bruce Archibald, Christian Kehlmaier, and Rolf Mathewes from a single partial female. The specific epithet is a matronym of Azure Rain Belgarde, who collected the type specimen, SR 08-06-02, and donated it to the

Stonerose Interpretive Center The Stonerose Interpretive center & Eocene Fossil Site is a 501c(3) non-profit public museum and fossil dig located in Republic, Washington. The center was established in 1989 and houses fossils that have been featured in ''National Geographic M ...

. Placement of the group has changed several times, with ''Metanephrocerus'' and ''Protonephrocerus'' being placed in the pipunculid subfamily Nephrocerinae as tribe Protonephrocerini from 1948 until 2014. The placement of the tribe was challenged in 2014 by Kehlmaier, Dierick and Skevington who suggested inclusion of the genera made Nephrocerinae paraphyletic. As such they elevated the tribe Protonephrocerini to the subfamily rank as Protonephrocerinae, leaving only '' Nephrocerus'' and '' Priabona'' in Nephrocerinae.

Description

''Metanephrocerus belgardeae'' is a large species, with a wing length of , and a hyaline wing coloration, broken by a smokey tone to the pterostigma and basal area of the wing. The wing has a long third section of the costal vein and the median vein that is long and straight. The females abdomen is approximately long, with short

seta In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

e on the

tergites 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 ...

, which grade to longer

on the first and second tergites. The short abdominal setae are distinct for the genus and exclude the species from other pipnculid genera. ''M. collini'' was known from 2 female specimens, which had hyaline wings with colored pterostigma. ''M. groehni'' is a nearly complete male fly with a total body length of , and is only missing the tip of the left hind leg. The hind legs show a distinct

chaetotaxy Chaetotaxy is the arrangement of bristles (macrochaetae) on an arthropod or annelid, or taxonomy based on their position and size. For example, it is important in Diptera, in which group it was formalised by Ernst August Girschner. The term chaeto ...

to the setae, with front sides having setae that are longer than the femur is wide. The eyes connect for three times the length of the

frons Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insec ...

. The wings are , though the wings are folded slightly and difficult to fully assess. The halters are darkened at the base and on the knob. ''M. hoffeinsorum'' is a whole male, though large portions of it are enclosed in white mold and the specimen has a total length of . The wings show a length of and have a covering of microtrichia. As with ''M. groehni'' the halters have darkened knobs and bases and the pteropleuron has 6 hairs on it. Tergite three of the abdomen is 1.3 times as long as tergite two.

References

{{Taxonbar, from=Q18926236 Ypresian insects Fossils of the United States Fossil taxa described in 2014 Fossil taxa described in 1939 Prehistoric insects of Europe Prehistoric insects of North America Pipunculidae Baltic amber Priabonian insects † Taxa named by Frank M. Carpenter Klondike Mountain Formation Prehistoric Diptera genera