''Metanephrocerus'' 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 big-headed flies in the

diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advance ...

n subfamily Protonephrocerinae, for which it is one of only two

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

. The genus contains four 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), ...

, ''Metanephrocerus belgardeae'', ''M. collini'', ''M. groehni'', and ''M. hoffeinsorum''. ''Metanephrocerus'' 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 Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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 (biology), isotype ...

were fossilized as inclusions in transparent chunks 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 ...

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

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

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

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 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 genus '' Protonephrocerus''. Carpenter and Hull's 1939

type description A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...

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 binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...

"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 (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

Klondike Mountain Formation The Klondike Mountain Formation is an Early Eocene (Ypresian) geological formation located in the northeast central area of Washington (state), Washington state. The formation is composed of volcanic rocks in the upper unit and volcanic plus lacu ...

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 In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

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), 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 Geo ...

. Placement of the group has changed several times, with ''Metanephrocerus'' and ''Protonephrocerus'' being placed in the pipunculid subfamily

Nephrocerinae Nephrocerinae is a subfamily of big-headed flies (insects in the family Pipunculidae). Genera * Tribe Nephrocerini ** Genus ''Nephrocerus ''Nephrocerus'' is a genus of flies belonging to the family Pipunculidae. The species of this genus ar ...

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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

. As such they elevated the tribe Protonephrocerini to the subfamily rank as Protonephrocerinae, leaving only ''

Nephrocerus ''Nephrocerus'' is a genus of flies belonging to the family Pipunculidae. The species of this genus are found in Europe, Asia and Northern America. Species *'' Nephrocerus acanthostylus'' Skevington, 2005 *'' Nephrocerus atrapilus'' Skevington, ...

'' and '' Priabona'' in Nephrocerinae.

Description

''Metanephrocerus belgardeae'' is a large species, with a wing length of , and a

hyaline A hyaline substance is one with a glassy appearance. The word is derived from , and . Histopathology Hyaline cartilage is named after its glassy appearance on fresh gross pathology. On light microscopy of H&E stained slides, the extracellula ...

wing coloration, broken by a smokey tone to the

pterostigma The pterostigma (plural: pterostigmata) is a group of specialized cells in the outer wings of insects, which are often thickened or coloured, and thus stand out from other cells. It is particularly noticeable in dragonflies, but present also in ...

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 female's abdomen is approximately long, with short

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e on the

tergites A ''tergum'' (Latin for "the back"; : ''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 'margin'. ...

, 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 chaet ...

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 Insect morphology is the study and description of the morphology (biology), 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 f ...

. 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 Eocene insects of Europe Eocene insects of North America Pipunculidae Baltic amber Priabonian insects

† A dagger, obelisk, or obelus is a typographical mark that usually indicates a footnote if an asterisk has already been used. The symbol is also used to indicate death (of people) or extinction (of species or languages). It is one of the mo ...

Taxa named by Frank M. Carpenter Klondike Mountain Formation Prehistoric Diptera genera