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Trilobite Zone
Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones. The ''Olenellus''-zone has traditionally marked the top of the Lower Cambrian, and is followed by the '' Eokochaspis'' zone. The last two zones of the Middle Cambrian are the '' Bathyuriscus– Elrathina''-zone (contemporaneous with the Burgess Shale) and the subsequent '' Bolaspidella''-zone (starting at the base of the Drumian stage). These are overlain by the lowermost Upper Cambrian ''Cedaria''-zone. Alternative zoning names place the Burgess Shale in the ''Peronopsis bonnerensis''-zone, which is underlain by the ''Oryctocephalus indicus''-zone (e.g. Spence Shale) and overlain (perhaps not directly) by the ''Ptychagnostus punctuosus''-zone. The lower Middle Cambrian '' Glossopleura''-zone (Spence Shale) is above the '' Albertella''-zone. The '' Elvinia''-zone is upper Cambrian. Subdivision of the ''Olenellus''-zone Recently, it has been proposed to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobites
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 Atdabanian stage of the Early Cambrian period () and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described. By the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized exoskeleton, they left an extensive fossil record. The stud ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drumian
The Drumian is a stage of the Miaolingian Series of the Cambrian. It succeeds the Wuliuan and precedes the Guzhangian. The base is defined as the first appearance of the trilobite ''Ptychagnostus atavus'' around million years ago. The top is defined as the first appearance of another trilobite ''Lejopyge laevigata'' around million years ago. The GSSP is defined in the ''Drumian section'' () in the Drum Mountains, Millard County, Utah, United States. The stage was also named after the Drum Mountains. The section is an outcrop of the Wheeler Formation The Wheeler Shale (named by Charles Walcott) is a Cambrian ( 507 Ma) fossil locality world-famous for prolific agnostid and ''Elrathia kingii'' trilobite remains (even though many areas are barren of fossils) and represents a Konzent ..., a succession of calcareous shales. The precise base of the Drumian is a laminated limestone above the base of the Wheeler Formation. References Cambrian geochronology Geo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lejopyge Laevigata
''Lejopyge laevigata'' is a species of agnostid trilobite belonging to the genus '' Lejopyge''. It existed during the Guzhangian to the Paibian Age (around to million years ago) of the Cambrian. It has a cosmopolitan distribution and is an important index fossil in biostratigraphy. Description ''Lejopyge laevigata'' exhibits a cephalon and pygidium that are smooth and almost featureless ( effaced). Both possess axial furrows that gradually become shallower until they disappear distally. They surround the rear edges of the glabella (reaching about as far or a little past the basal glabellar lobes) and the anterior end of the central lobe of the pygidium. Basal furrows are also present. The genae ("cheeks") are usually smooth, but in extremely rare cases they may possess small pits (scrobicules) of moderate depth. The border around the pygidium is uniform in width at the back and narrows towards the front. Like all members of the suborder Agnostina, ''Lejopyge laevigata'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 genus probably ranged throughout the water column. It has two glabellar lobes, and three pygidial lobes. Type species ''Agnostus punctuosus'' Angelin, 1851 from the ''Pt. punctuosus'' Zone of the Alum Shale (Drumian), Sweden (by original designation). Official ruling on the conservation of accepted usage of ''A. punctuosus'' as the type species was given by the International Commission on Zoological Nomenclature, 1993. Remarks ''Ptychagnostus affinis'' (Brøgger 1878) was once considered a subspecies of ''Pt. punctuosus''. Laurie (2008) grouped ''punctuosus'' and ''affinis'' within ''Ptychagnostus'', but preferred to place the closely related ''atavus'' within ''Acidusus''. Ptychagnostidae Genera Høyberget & Bruton (2008) HØYBERGET M. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guzhangian
The Guzhangian is an uppermost stage of the Miaolingian Series of the Cambrian. It follows the Drumian Stage and precedes the Paibian Stage of the Furongian Series. The base is defined as the first appearance of the trilobite ''Lejopyge laevigata'' around million years ago. The Guzhangian-Paibian boundary is marked by the first appearance of the trilobite ''Glyptagnostus reticulatus'' around million years ago. The name Guzhangian is derived from Guzhang County, Hunan Province, China. The GSSP is defined in the Huaqiao Formation in Hunan. The precise base of the Guzhangian is a limestone layer 121.3 m above the base Huaqiao Formation(花桥组) at the Louyixi section (), where ''Lejopyge laevigata ''Lejopyge laevigata'' is a species of agnostid trilobite belonging to the genus '' Lejopyge''. It existed during the Guzhangian to the Paibian Age (around to million years ago) of the Cambrian. It has a cosmopolitan distribution and is an ...'' has its first appearance. R ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Miaolingian
The Miaolingian is the third Series of the Cambrian Period, and was formally named in 2018. It lasted from about to million years ago and is divided in ascending order into 3 stages: the Wuliuan, Drumian, and Guzhangian. The Miaolingian is preceded by the unnamed Cambrian Series 2 and succeeded by the Furongian series. Definition A number of proposals for fossils and type sections were made before it was formally ratified in 2018. The most promising fossil markers were seen to be the respective first appearances of either trilobite species ''Ovatoryctocara granulata'' or ''Oryctocephalus indicus'', which both have an age close to million years ago. After some deliberation, the FAD of ''Oryctocephalus indicus'' was chosen to be the lower boundary marker, and the GSSP was placed in Wuliu-Zengjiayan, Guizhou, China. The Miaolingian-Furongian boundary has the same definition as the Paibian Stage. It is defined as the first appearance of ''Glyptagnostus reticulatus ''Glyptagn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glyptagnostus Reticulatus
''Glyptagnostus reticulatus'' is a species of agnostid trilobite belonging to the genus '' Glyptagnostus''. It existed during the Paibian Age ( million years ago) of the Cambrian. It has a cosmopolitan distribution and is an important index fossil in biostratigraphy. It was characterized by an unusual net-like pattern of furrows on both the cephalon and the pygidium. Description Like all members of the suborder Agnostida, ''Glyptagnostus reticulatus'' is completely blind and only has two thoracic segments. The cephalon and pygidium are more or less the same size and shape ( isopygous). The glabella of the cephalon has two lobes. The front lobe is roughly squarish in shape, while the rear lobe is elongated and split along the middle. The cephalon has a narrow well-defined border. The pygidium has a long tapering central axis which can be divided into three lobes. The axis is connected to the rear margin by a central furrow. At both sides of the axis are a row of four or more pi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 reticulatus'' around million years ago. The top, or the base of the Jiangshanian is defined as the first appearance of the trilobite ''Agnostotes orientalis'' around million years ago. The name is derived from Paibi, a village in Hunan, China. The GSSP is defined in the "Paibi section" (Wuling Mountains, Huayuan County), an outcrop of the Huaqiao Formation(花桥组). The base is the first occurrence of ''Glyptagnostus reticulatus'' which is 396 m above the base of the Huaqiao Formation Huaqiao may refer to: *Overseas Chinese (华侨), or Huaqiao in pinyin *Huaqiao University (华侨大学), in Quanzhou, Fujian *Huaqiao railway station (花桥站), station of the Shanghai-Nanjing Intercity High-Speed Railway in Shanghai *Huaqiao s ... at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agnostotes Orientalis
''Agnostotes orientalis'' is a species of agnostid trilobite belonging to the genus '' Agnostotes''. It existed during the Jiangshanian Age ( million years ago) of the Cambrian. It is an important index fossil in biostratigraphy. Description ''Agnostotes orientalis'', like all members of the suborder Agnostina, possesses two thoracic segments, has a cephalon and pygidium that are more or less the same size and shape ( isopygous), and is completely blind. The axial lobe of the cephalon is narrow. At the front of the glabella is a notch (frontal sulcus), a characteristic unique to the species, making it easy to distinguish from other members of the genus. The posterior end of the axial lobe of the pygidium also widens significantly, another distinct characteristic of the species. Along the margins of the pygidium are a pair of very small backward-pointing spines. Both the pygidium and the cephalon are ornamented with small pits (scrobicules) and wrinkles, extending mostly inwards ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jiangshanian
The Jiangshanian is the middle stage of the Furongian series. It follows the Paibian Stage and is succeeded by the still unnamed Stage 10 of the Cambrian. The base is defined as the first appearance of the trilobite ''Agnostotes orientalis'' which is estimated to be million years ago. The Jiangshanian lasted until approximately million years ago. The Cambrian stage was named after Jiangshan, a city in China's Zhejiang province. The GSSP of the Jiangshanian is the "Duibian B Section" (), west of the village of Duibian(碓边), and 10 km north of Jiangshan Jiangshan () is a county-level city located in Quzhou prefecture-level city, in the southwest of Zhejiang Province, China, bordering Jiangxi province to the west. Located about 250 kilometers southwest of Hangzhou, the provincial capital, it is .... The outcrop belongs to the Huayansi Formation(华严寺组). References Cambrian geochronology Geological ages {{Geology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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