Ptychagnostidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of agnostid

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s from the 5th Stage to the

Paibian The Paibian is the lowest stage of the Furongian Series of the Cambrian System. The Paibian is also the first age of the Furongian Epoch of the Cambrian Period. It follows the Guzhangian ( Miaolingian series of the Cambrian) and is succeede ...

Age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

( to

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

). 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 Biology ...

Description

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

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of 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 di ...

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somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryogenesis, embryonic stage of somitogenesis, along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

s). They are completely blind.

Distribution and age range

Ptychagnostidae has a

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

. 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 b ...

to the

of the early

Furongian The Furongian is the fourth and final epoch and series of the Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding ...

Epoch in the

( 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 Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

Agnostina Agnostida are an order of extinct arthropods which have classically been seen as a group of highly modified trilobites, though some recent research has doubted this placement. Regardless, they appear to be close relatives as part of the Artiopod ...

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Agnostida Agnostida are an order of extinct arthropods which have classically been seen as a group of highly modified trilobites, though some recent research has doubted this placement. Regardless, they appear to be close relatives as part of the Artiopod ...

. 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 as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Teiichi Kobayashi in 1939. Its name comes from the

type genus In biological taxonomy, the type genus (''genus typica'') 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-bearin ...

, '' Ptychagnostus''. It includes the following

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 ...

(with their

taxonomic synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The Botanical nomenclature, botanical and Zoological nomenclature, zoological codes of nomencl ...

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 *'' Ptychagnostus'' 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