''Eoplectreurys'' 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 ...

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

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 ...

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

from the family

Plectreuridae Plectreuridae, also called plectreurid spiders, is a small spider family confined to the Southwestern United States, Mexico, and the Caribbean. Only two living genera are known—the nominate genus '' Plectreurys'' and '' Kibramoa''. In the pa ...

, with a sole species, ''Eoplectreurys gertschi''. The fossils of ''Eoplectreurys'' were recovered from the ~164 Ma old

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

Daohugou formation The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period (Bathonian- Oxfordian stages). It is known for its exceptionally preserved fossils, including those of ...

tuffs in

Inner Mongolia Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an autonomous region of the People's Republic of China. Its border includes most of the length of China's border with the country of Mongolia. Inner Mongolia also accounts for a ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

History and classification

The

type specimens In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes t ...

are deposited in the Nanjing Institute of Geology and Palaeontology with the genus being described from a total of seven adult spiders. ''Eoplectreurys'' was first studied and described by Drs Paul Selden and Diying Huang, who published their

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 ...

in the journal ''

Naturwissenschaften ''The Science of Nature'', formerly ''Naturwissenschaften'', is a monthly peer-reviewed scientific journal published by Springer Science+Business Media covering all aspects of the natural sciences relating to questions of biological significance. I ...

'' in 2010. The genus name is a combination of 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 ...

word ''eos'', which means "dawn", and ''Plectreurys'' the name of the modern genus which the fossils closely resemble. ''Eoplectreurys'' is considered the oldest described spider genus of the Haplogynae series, predating the described Haplogynae spiders from

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

ambers in

Jordan Jordan ( ar, الأردن; tr. ' ), officially the Hashemite Kingdom of Jordan,; tr. ' is a country in Western Asia. It is situated at the crossroads of Asia, Africa, and Europe, within the Levant region, on the East Bank of the Jordan Rive ...

and

Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon () or the Lebanese Republic, is a country in Western Asia. It is located between Syria to the north and east and Israel to the south, while Cyprus li ...

, and is the oldest member of Plectreuridae. The two other Plectreuridae species described from fossils are both known from specimens preserved in amber with ''Palaeoplectreurys baltica'' from Eocene

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 ''Plectreurys pittfieldi'' from early Miocene

Dominican amber Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree ''Hymenaea protera''. Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil incl ...

. The modern distribution of Plectreuridae is restricted to Southwestern

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, Central America, and parts of the Greater Antilles. The current restricted range of the family may be due to either the severe cooling at the Eocene–

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

transition or the Pliocene– Pleistocene ice age.

Description

The specimens of ''Eoplectreurys'' are preserved as compression fossils in the fine-grained lacustrian rocks and thus have been flattened from their dimensions in life. Due to the lack of exterior genitalia on females, it is very difficult to identify possible ''Eoplectreurys'' females from among the number of Haplogynae spiders found in the Daohugou formation. Only one specimen is a possible match, having a carapace that is round as in the ''Eoplectreurys'' males, while the other known Haplogynae female specimens possess elongated carapaces. Only one other family of spiders,

Segestriidae Tube-dwelling spiders (Segestriidae) are a family of araneomorph spiders first described by Eugène Simon in 1893. It consists of five genera, two large and widespread, '' Segestria'' and ''Ariadna'', and three smaller genera, '' Citharoceps'', ...

, is similar to the fossils. However the legs of Segestriidae have more spines than the fossils and the overall carapace shape of Segestriids is elongated, with

maxillae 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. The t ...

that do not meet in front of the labium. On average ''Eoplectreurys'' was a small spider with the average body length, not including legs, being . The fossils display fused chelicerae, distinctly short legs, and are ecribellate, that is, without the silk spinning organ called a cribellum. The number of eyes is not distinguishable in the fossils and the stridulating file on the pedipalps are not apparent or not present. ''Eoplectreurys'' is most similar in structure to the ''P. tristis'' group of ''

Plectreurys ''Plectreurys'' is a genus of plectreurid spiders that was first described by Eugène Louis Simon in 1893. It is one of only two genera in its family. Species it contains twenty-three species, found in Costa Rica, Guatemala, Mexico, the United ...

''. The species lived around a lake in a volcanically active area and was found in fine-grained volcanic ash lacustrine (lake-bed) deposits, the ash helping to preserve the specimens.

References

{{Taxonbar, from=Q3008658 Plectreuridae Jurassic arachnids Jurassic animals of Asia Prehistoric arthropods of Asia Fossil taxa described in 2010 Transitional fossils Monotypic Araneomorphae genera Spiders of China