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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 Artiopoda. They are present in the Lower Cambrian fossil record along with trilobites from the Redlichiida, Corynexochida, and Ptychopariida orders, and were highly diverse throughout the Cambrian. Agnostidan diversity severely declined during the Cambrian-Ordovician transition, and the last agnostidans went extinct in the Late Ordovician. Systematics The Agnostida are divided into two suborders — Agnostina and Eodiscina — which are then subdivided into a number of families. As a group, agnostids are isopygous, meaning their pygidium is similar in size and shape to their cephalon. Most agnostid species were eyeless. The systematic position of the order Agnostida within the class Trilobita remains uncertain, and there has been c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 successful of all early animals, existing in oceans for almost 270million years, with over 22,000 species having been described. Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton made of calcite, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolution, evolutionary biology, and plate tectonics. Trilobites are placed within the clade Artiopoda, which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised. The relationship of Artiopoda to other arthropods is uncertain. Trilobites evolved into many ecological niches; some moved over the seabed as predators, scavengers, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobites
Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, existing in oceans for almost 270million years, with over 22,000 species having been described. Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton made of calcite, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology, and plate tectonics. Trilobites are placed within the clade Artiopoda, which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised. The relationship of Artiopoda to other arthropods is uncertain. Trilobites evolved into many ecological niches; some moved over the seabed as predators, scavengers, or filter feeders, and some swam, feeding o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 Artiopoda. They are present in the Lower Cambrian fossil record along with trilobites from the Redlichiida, Corynexochida, and Ptychopariida orders, and were highly diverse throughout the Cambrian. Agnostidan diversity severely declined during the Cambrian-Ordovician transition, and the last agnostidans went extinct in the Late Ordovician. Systematics The Agnostida are divided into two suborders — Agnostina and Eodiscina — which are then subdivided into a number of families. As a group, agnostids are isopygous, meaning their pygidium is similar in size and shape to their cephalon. Most agnostid species were eyeless. The systematic position of the order Agnostida within the class Trilobita remains uncertain, and there has been conti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eodiscoidea
Eodiscina is trilobite suborder. The Eodiscina first developed near the end of the Lower Cambrian period (late Atdabanian) and became extinct at the end of the Middle Cambrian. Species are tiny to small, and have a thorax of two or three segments. Eodiscina includes six families classified under one superfamily, Eodiscoidea. Taxonomy The Eodiscina are mostly considered the more primitive suborder of the Agnostida, and the Agnostina the more advanced. Some scholars do not consider the Agnostina true trilobites, and consequently rejected the idea that they were related to the Eodiscina. Consequently, these scientists have proposed to elevate the group to ordinal level, which would thus be called Eodiscida Kobayashi, 1939. Origin The oldest known eodiscoid is '' Tsunyidiscus''. The glabella of ''Tsunyidiscus'' is extremely similar to that of ''Dipharus clarki'', and distinct from all other eodiscoids. ''D. clarki'' is thought to represent an immature stage of the redlichioid ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eodiscina
Eodiscina is trilobite suborder. The Eodiscina first developed near the end of the Cambrian, Lower Cambrian period (late Atdabanian) and became extinct at the end of the Middle Cambrian. Species are tiny to small, and have a thorax of two or three segments. Eodiscina includes six Family (biology), families classified under monotypic taxon, one superfamily (biology), superfamily, Eodiscoidea. Taxonomy The Eodiscina are mostly considered the more primitive suborder of the Agnostida, and the Agnostina the more advanced. Some scholars do not consider the Agnostina true trilobites, and consequently rejected the idea that they were related to the Eodiscina. Consequently, these scientists have proposed to elevate the group to Order (biology), ordinal level, which would thus be called Eodiscida Kobayashi, 1939. Origin The oldest known eodiscoid is ''Tsunyidiscus''. The glabella of ''Tsunyidiscus'' is extremely similar to that of ''Dipharus clarki'', and distinct from all other eodis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agnostidae
Agnostidae is a family (biology), family of Agnostida trilobites. Like all Agnostina, they were eyeless and had only two thorax, thoracic segments. These trilobites inhabited benthic waters worldwide from 508 to 461 million years ago. The family includes the following genera, among others: *''Acmarhachis'' *''Agnostus'' *''Aistagnostus'' *''Anglagnostus'' *''Biciragnostus'' *''Connagnostus'' *''Distagnostus'' *''Eolotagnostus'' *''Gymnagnostus'' *''Homagnostus'' *''Idolagnostus'' *''Innitagnostus'' *''Ivshinagnostus'' *''Kymagnostus'' *''Lotagnostus'' *''Micragnostus'' *''Obelagnostus'' *''Oncagnostus'' *''Phalacroma'' *''Phalagnostus'' *''Quadrahomagnostus'' *''Raragnostus'' *''Semagnostus'' *''Strictagnostus'' *''Trilobagnostus'' References Agnostidae, Agnostoidea Trilobite families Cambrian first appearances Middle Ordovician extinctions {{agnostida-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ptychagnostidae
Ptychagnostidae is a family of agnostid trilobites from the 5th Stage to the Paibian Age of the Cambrian ( to million years ago). The family includes several important index fossils. Description Like all agnostids, ptychagnostids have cephalons and pygidia that are more or less uniform in size and shape ( isopygous). The thorax is composed of two body segments (somites). They are completely blind. Distribution and age range Ptychagnostidae has a cosmopolitan distribution. They existed during the 5th Stage of the Series 3 Epoch to the Paibian Age of the early Furongian Epoch in the Cambrian ( to million years ago). 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 paleontologist Teiichi Kobayashi in 1939. Its name comes from the type genus, '' Ptychagnostus' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calodiscidae
The Calodiscidae Kobayashi, 1943 'nom. transl.'' Öpik, 1975 ''ex'' Calodiscinae Kobayashi, 1943are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian (Botomian and Toyonian). They are small or very small, and have a thorax of two or three segments. The Calodiscidae includes five genera (see box). Taxonomy The probable ancestors of the Calodiscidae are among the Tsunyidiscidae. The Calodiscidae had no descendants. cited ''in'' Description Like all Agnostida, the Calodiscidae are diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. The central raised area of the cephalon (or glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior ...) has parallel si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eodiscidae
Eodiscidae is a family of agnostid trilobites that lived during the final Lower Cambrian (late Toyonian) and the Middle Cambrian. They are small or very small, and have a thorax of two or three segments. Eodiscidae includes nine genera (see box). Taxonomy The Eodiscids probably descended from the agnostids of family Yukoniidae. cited in Description Like other agnostids, the body of eodiscids is diminutive, the headshield (or cephalon) and tailshield (or pygidium) are of approximately same size, with 2 or 3 thoracic segments in-between, each consisting of a horizontal inner portion that abruptly passes into an inclined outer portion (fulcrate). The central raised area of the cephalon (or glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior ...) is narrow, usually with par ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peronopsidae
The Peronopsidae (which may also be called peronopsids) comprise the earliest family of the Agnostina suborder. Species of this family occurred on all Supercontinent, paleocontinents. The earliest representatives of this family first occur just before the start of the Middle Cambrian, and the last disappeared just after the start of the Upper Cambrian. Distribution Peronopsidae are Cosmopolitan distribution, cosmopolitan. Temporal distribution Temporal distribution: * ''Archaeagnostus'', Toyonian (Trilobite zone#Subdivision of the Olenellus-zone, ''Nephrolenellus multinodus''-zone) and Amgan, Amgaian (''Trilobite zone, Ovatoryctocara''-zone). * ''Eoagnostus'', Toyonian (''Nephrolenellus multinodus''-zone) and Amgaian (''Ovatoryctocara''-zone). * ''Peronopsis, Peronopsis (Proacadagnostus)'', Amgaian (''Ovatoryctocara''- and lower ''Kounamkites''-zones). * ''Diplorrhina'', Amgaian (''Ovatoryctocara''- and ''Kounamkites''-zones) * ''Peronopsis, Peronopsis (Peronopsis)'', Amgaian ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hebediscidae
Hebediscidae is a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian (Atdabanian to Toyonian). They are small or very small, and have a thorax of two or three segments. The Hebediscidae include five genera (see box). Taxonomy The Hebediscidae probably descended from the Tsunyidiscidae and gave rise to the Weymouthiidae. cited in Description Like all Agnostida, the Hebediscidae are diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. In the Hebediscidae, the central raised area of the cephalon (or glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior ...) is wide at its rear end, has parallel sides or tapers forward, and without transverse glabellar fu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tsunyidiscidae
''Tsunyidiscus'' is a trilobite belonging to the suborder Eodiscina. ''Tsunyidiscus'' appeared near the end of the Lower Cambrian, during the late Atdabanian stage of geologic time and some collections suggest it may have survived into the Botomian. The genus is very small (up to 7mm), oculate and isopypous with a narrow dome-shaped glabella and a narrow bullet-shaped pygidial axis. Thorax consists of three segments. ''Tsunyidiscus'' is the only genus currently attributed to the family Tsunyidiscidae.Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997 Description Like other Agnostida the body of ''Tsunyidiscus'' is diminutive, the headshield (or cephalon) and end-section (pygidium) are of approximately same size ( isopygous), with 3 thoracic segments in-between, each consisting of a horizontal inner portion that abruptly passes into an inclined outer portion (fulcrate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
