''Neoephemera antiqua'' is an extinct

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 ...

of square-gill mayfly in the family Neoephemeridae that is known from early

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'', " ...

Ypresian stage 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 ...

, lake deposits near the small community of Republic in

Ferry County, Washington Ferry County is a county located on the northern border of the U.S. state of Washington. As of the 2020 census, the population was 7,178, making it the fourth-least populous county in Washington. The county seat and largest city is Republic. T ...

, USA.

History and classification

''Neoephemera antiqua'' is known only from one fossil, 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 ...

, number "UWBM76324". It is a single, mostly complete naiad of undetermined sex, preserved as a compression fossil in fine grained shale. The fossil specimen is from the

University of Washington The University of Washington (UW, simply Washington, or informally U-Dub) is a public research university in Seattle, Washington. Founded in 1861, Washington is one of the oldest universities on the West Coast; it was established in Seattl ...

site number UWBM A0307B which works sediments from the Tom thumb tuff member of the Klondike Mountain Formation. Outcrops of the formation are found in and around Republic. The type specimen is currently preserved in the paleoentomology collections housed in the

Burke Museum of Natural History and Culture The Burke Museum of Natural History and Culture (Burke Museum) is a natural history museum in Seattle, Washington, in the United States. Established in 1899 as the Washington State Museum, it traces its origins to a high school naturalist club fo ...

, part of the

Seattle, Washington Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region ...

, USA. ''N. antiqua'' was first studied by Nina D. Sinitchenkova of the Paleontological Institute of the

Russian Academy of Sciences The Russian Academy of Sciences (RAS; russian: Росси́йская акаде́мия нау́к (РАН) ''Rossíyskaya akadémiya naúk'') consists of the national academy of Russia; a network of scientific research institutes from across ...

, with her 1999 type description being published in the Russian text ''Palaeontological Journal''. The specific epithet ''antiqua'' was coined from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

"antiquus", meaning old. When the holotype of ''Neoephemera antiqua'' was first described by Sinitchenkova, The Klondike Mountain Formation as assigned a Middle Eocene age. Further refinement of the dating has resulted in the formation being given a slightly older age, placing it in the Ypresian stage of the late Early Eocene. ''Neoephemera antiqua'' is the oldest known occurrence of the family Neoephemeridae, being older than the Oligocene species '' Potamanthellus rubiens'', described from Montana in 1977 by Standley Lewis.

Description

The compression fossil of the naiad is preserved dorsal side up and is nearly complete, only missing the head, ends of the fore and middle legs, and the ends of the three caudal filaments. The full naiad is estimated to have been in length, and is distinguishable from other species of neoepherids by is shorter

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 the structure of the posterior margins of the abdominal segments. The side margins of the pronotum are moderately dilated. The gill opercula have a diagonal rib and the anterolateral angles of 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 ...

have distance processes. Both of these features are only found in the modern genus ''Neoephemera'' leading to the placement of the fossil species in the genus.

References

{{Taxonbar, from=Q6992784 Mayflies Ypresian insects Eocene insects of North America Prehistoric insects of North America Fossil taxa described in 1999 Klondike Mountain Formation