Ptychagnostidae is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of agnostid

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s from the 5th Stage to the

Paibian The Paibian is the lowest stage of Furongian series of the Cambrian. It follows the Guzhangian ( 3rd series of the Cambrian) and is succeeded by the Jiangshanian Stage. The base is defined as the first appearance of the trilobite '' Glyptagnostus ...

Age of the Cambrian ( to

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

). The family includes several important

index fossil Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...

Description

Like all agnostids, ptychagnostids have cephalons and pygidia that are more or less uniform in size and shape ( isopygous). The

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

is composed of two body segments (

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide ...

s). They are completely blind.

Distribution and age range

Ptychagnostidae has a cosmopolitan distribution. They existed during the 5th Stage of the

Series 3 Series 3 may refer to: * 3 Skypephone Series, the mobile phone series * Apple Watch Series 3, smart watch * Aston Martin Lagonda Series 3, the automobile model * Aston Martin V8 Series 3, the automobile model * BMW 3 Series, the automobile model li ...

Epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

to the

Age of the early

Furongian The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three ...

Epoch in the Cambrian ( to

). The earliest member of the family is '' Ptychagnostus praecurrens'' from the Burgess Shale fauna.

Taxonomy

Ptychagnostidae is classified under the superfamily Agnostoidea of the suborder Agnostina, order Agnostida. The family was first established by the

Japanese Japanese may refer to: * Something from or related to Japan, an island country in East Asia * Japanese language, spoken mainly in Japan * Japanese people, the ethnic group that identifies with Japan through ancestry or culture ** Japanese diaspor ...

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Teiichi Kobayashi in 1939. Its name comes from the

type genus In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearing type of a nominal ...

, ''

Ptychagnostus ''Ptychagnostus'' is a member of the agnostida that lived during the Cambrian period. Ptychagnostidae generally do not exceed one centimetre in length. Their remains are rarely found in empty tubes of the polychaete worm '' Selkirkia''. The gen ...

''. It includes the following genera (with their

taxonomic synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Lin ...

s): *'' Allobodochus'' Opik, 1979 *'' Criotypus'' Opik, 1979 *'' Goniagnostus'' Howell, 1935 *'' Lejopyge'' Hawle & Corda, 1847 : = ''Miagnostus'' *'' Myrmecomimus'' Opik, 1979 *'' Onymagnostus'' Opik, 1979 := ''Agnostonymus'' *'' Pseudophalacroma'' Pokrovskaya, 1958 *''

'' Jaekel, 1909 :=''Triplagnostus'', ''Huarpagnostus'', ''Solenagnostus'', ''Pentagnostus'', ''Aristarius'', ''Aotagnostus'', ''Acidusus'', ''Canotagnostus'', ''Zeteagnostus'' *'' Schismagnostus'' Robison, 1994 *'' Tomagnostella'' Kobayashi, 1939a *'' Tomagnostus'' Howell, 1935 *'' Yakutiana'' Özdikmen, 2009

References

External links

* * {{Taxonbar, from=Q1241316 Cambrian trilobites Agnostoidea Trilobite families Miaolingian first appearances Miaolingian extinctions Paibian