Lotagnostus

Lotagnostus; Temporal range: Upper Cambrian (upper Sunwaptan) PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Order:	Agnostida
Family:	Agnostidae
Subfamily:	Agnostinae
Genus:	Lotagnostus; Whitehouse, 1936
species
	L. trisectus Salter, 1864 (type) synonym Agnostus trisectus; L. americanus Billings, 1860 synonym Agnostus americanus; L. asiaticus Troedsson, 1937 possible synonym L. spectabilis; L. attenuatusRusconi, 1955; L. ergoidesShergold, 1972; L. germanicusMatthew, 1901 synonym Agnostus trisectus germanicus; L. hedeniTroedsson, 1937 synonym Agnostus hedeni; L. irretinusShergold, 1975; L. matthewiWestrop & Landing, 2017; L. obscurus Palmer, 1955; L. peladensisRusconi, 1951; L. punctuatusLu, 1964; L. salteriWestrop & Landing, 2017;

Last updated April 15, 2022

Lotagnostus is a genus of very small trilobites in the order Agnostida, which lived on the outer continental shelves worldwide, during the late Upper Cambrian. It was described by Whitehouse in 1936, and the type species is Lotagnostus trisectus, which was originally described as a species of Agnostus by Salter in 1864.^[1]

Taxonomy

The Treatise on Invertebrate Paleontology ^[2] divides Lotagnostus into three subgenera that differ in the degree of effacement: L. (Lotagnostus)Whitehouse, 1936 (neither cephalon nor pygidium strongly effaced), L. (Distagnostus)Shergold, 1972 (strongly effaced on the outer/dorsal surface, but with clear furrows on the inner/ventral surface and L. (Eolotagnostus)Zhou in Zhiqiang Zhou, li & Qu, 1982 (with even the inner/ventral surface strongly effaced). Later authors however consider it likely that creating these subgenera would render the nominate subgenus paraphyletic.^[3]

Biostratographic significance

The first appearance datum (FAD) of Lotagnostus americanus has been proposed to define the lower limit of Cambrian Stage 10.^[4] This proposition is based on the interpretation that L. americanus is a polymorph species with a global distribution, a concept that included L. obscurus, and Agnostus trisectus, the type of Lotagnostus. Recently however, the North American species of Lotagnostus have been revised and it was concluded that L. americanus in fact shows little variation and has a limited spatial distribution, and the variants from other locations belong to several other Lotagnostus species.^[3] This renders L. americanus unfit as index fossil for the lower limit of Cambrian Stage 10. As alternatives the FADs of the conodonts Cordylodus andresi and Eoconodontus notchpeakensis have been suggested.^[3]

Distribution

L. trisectus is known from the late Upper Cambrian of Canada (MacNeil Brook, Middle Chesley Drive Group, Nova Scotia), England (White Leaved Oak Shale, Malvern, Gloucestershire), Wales (Cwmhesgen Formation) and Sweden (Andrarum).
L. americanus occurs at the late Upper Cambrian of Canada (in boulders in conglomerates of the Léwis Formation, North Ridge, near Léwis, Quebec).
L. asiaticus has been found in the late Upper Cambrian of China (Kuruktagh, Xinjiang)
L. germanicus is known from the late Upper Cambrian of Canada (North shore of East Bay, near Eskasoni, Cape Breton Island, Middle Chesley Drive Group, Nova Scotia)
L. hedeni occurs at the late Upper Cambrian of China (Kuruktagh, Xinjiang; Siyangshan Formation, western Zhejiang), Kazakhstan (Euloma limitaris-Taoyuania zone) and Canada (Phylacterus saylesi fauna, Shallow Bay Formation, western Newfoundland)
L. obscurus is present in the late Upper Cambrian of the United States (Pogonip Limestone, Windfall Formation, near Hamburg Shaft, Eureka District, Nevada))
L. peladensis is known from the late Upper Cambrian of Argentina (Precordillera)
L. punctuatus has been found in the late Upper Cambrian of China (Zejiang; elsewhere in Southeastern China) and Kazakhstan.

Lotagnostus is also present in Siberia (Ogon'or Formation along the Khos-Negele River), but its assignment to a particular species is difficult.

Description

Like all Agnostida, Lotagnostus is diminutive, with the headshield (or cephalon) and tailshield (or pygidium) of approximately the same size (or isopygous) and outline. Like all Agnostina, Lotagnostus has only two thorax segments. The species are characterized by variable stages of effacement, more so on the outer/dorsal surface compared to the inner/ventral surface. This may complicate distinction from effaced species in other genera. The frontal lobe the central raised area of the cephalon (or glabella) is long at about ⅓ or more of the length of the glabella. The basal lobes at the rear of the glabella are narrow triangular and equal in length to the frontal lobe. The central part of the glabella has two side lobes. Opposite the tip of the side lobes there is a node on the midline. There is a furrow at midline connecting the glabella with the border furrow. The axis of the pygidium (or rhachis) has three sections. The frontal section is split into three parts. Both lateral parts are defined by furrows on all sides: those with the central section directed backward and very slightly outward, those with the middle section outward and slightly backward, and those with the pleural zone backward and slightly inward. The middle part is merged with the central section. The middle part carries a node. The furrow between the central and rear parts is transverse, and those with the pleural zone backward and slightly inward. The rear part is about twice as long as the frontal and central parts individually. The surrounding axial furrow is directed outward, than strongly bends backward and than curves regularly ever more inward. Over the posterior ⅔ of the rear part a strip about as wide as the node on the central part may be discernible, which ends in a node that at the very rear of the rhachis. The distance between the rhachis and the border furrow (or post axial length) is about equal to ¼ of the rhachis. The pygidial border is about ⅛ of the rhachis. Opposite to the rear of the rhachis the border may carry a small spine at each side.^[3]

Related Research Articles

Agnostus, is a genus of agnostid trilobite belonging to the Family Agnostidae, that lived during the late Middle Cambrian – early Upper Cambrian. It is the type genus of the family Agnostidae and is subdivided into two subgenera, Agnostus and Homagnostus.

Dikelocephalus is a genus of very large trilobites of up to 50 cm (20 in) long, that lived during the last 3 million years of the Cambrian (Sunwaptan). Their fossils are commonly found as disarticulated sclerites, in the upper Mississippi Valley and in Canada (Alberta). The exoskeleton is rounded anteriorly, with the thorax and sides of the tailshield slightly tapering to about ⅔× of the width across the base of the spines at the back of the headshield. At the side corners of the pygidium there may be triangular or hooked spines, pointing backwards, while between the spines the posterior margin is at a 30-75° angle with the lateral margin, gently convex or nearly straight. If pygidial spines are lacking, the margin is gradually rounded. The thorax has 12 segments.

Acimetopus Rasetti, 1966, is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi (1943), Order Agnostida Salter (1864). It lived during the Botomian stage. = late Lower Cambrian Stage 4 ; the upper Botomian boundary corresponds to base of the Middle Cambrian, Miaolingian Series and Wuliuan stage.

Analox Rasetti, 1966 is a genus of Eodiscinid trilobites belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida It lived during the Botomian stage. It can easily be distinguished from other trilobites by the two furrows that extend forwards and sidewards from the front of the glabella.

Egyngolia is a genus of very small sized Trilobites, that lived during the Lower Cambrian in what are today the Russia Federation, Mongolia, and South Australia.

Acadagnostus is a genus of trilobite from the Middle Cambrian, with 7 species currently recognized. The type species A. acadicus has the widest distribution known from any peronopsid and has been found in North America, Greenland, England, Western Europe, Eastern Europe, Central Asia, the Altai Mountains, the Siberian shield, China, and Australia.

Acmarhachis is a genus of trilobite in the order Agnostida, which lived in what are now Australia, Canada, China (Anhui), Kazakhstan, Russia (Kharaulakh), and the US. It was described by Resser in 1938, and the type species is Acmarhachis typicalis.

Phalagnostus is a genus of small trilobites, in the order Agnostida. It lived during the Middle Cambrian, in what are now Canada, China, the Czech Republic, Denmark, England, France, the Russian Federation, Wales, Sweden, and possibly the United States (Vermont). The headshield is almost entirely effaced and wider than the tailshield. The pygidium is also very effaced, but the ovate pygidial axis is well defined and a border furrow is also present.

Lejopyge laevigata is a species of agnostid trilobite belonging to the genus Lejopyge. It existed during the Guzhangian to the Paibian Age of the Cambrian. It has a cosmopolitan distribution and is an important index fossil in biostratigraphy.

Glyptagnostus reticulatus is a species of agnostid trilobite belonging to the genus Glyptagnostus. It existed during the Paibian Age 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.

Agnostotes orientalis is a species of agnostid trilobite belonging to the genus Agnostotes. It existed during the Jiangshanian Age of the Cambrian. It is an important index fossil in biostratigraphy.

Galbagnostus is an extinct genus of agnostid trilobite. It lived during the Lower and Middle Ordovician.

The Peronopsidae comprise the earliest family of the Agnostina suborder. Species of this family occurred on all 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.

Thoracocare is a minute to very small trilobite, that lived during part of the Middle Cambrian in what are today the states of Idaho, Nevada and Utah. It is the only trilobite known with just two thorax segments outside most members of the Agnostida order. It can be distinguished from Agnostida by the very wide subquadrate glabella, parallel-side or widening forward in the largest specimen, with the full front side touching the border. Two species are known, one, T. idahoensis, only from pygidia.

Diplorrhina Hawle and Corda (1847) is a genus of trilobite belonging to Order Agnostida. It lived during the early Middle Cambrian in what are now the Czech Republic and the North Siberian plateau. as in members of the family Peronopsidae it lacks a preglabellar furrow. Both cephalon and pygidium lack spines. It is difficult to distinguish Diplorrhina from many other peronopsids.

Geragnostus is a genus of very small agnostid trilobites whose fossils are found Ordovician-aged marine strata from Eurasia, North America and Argentina.

Toragnostus is a genus of trilobites restricted to the late Middle Cambrian. Its remains have been found in the United States, Greenland, Denmark, China, Sweden, the Russian Federation, and Kazakhstan. Its headshield and tailshield are almost completely effaced and it has two thorax segments.

Ovatoryctocara is a genus of small corynexochid trilobites from the Cambrian, that lived in what now are Siberia, China, Greenland and Canada (Newfoundland). Ovatoryctocara can be recognised by the combination of the following characters: the central raised area of the cephalon is approximately cylindrical and has two rows of four triangular or round pits. The thorax only has 5 or 6 segments. The tailshield has an axis of 6 to 12 rings, the pleural furrows are well developed and the border is absent or narrow as a hair.

Eodiscidae is a family of agnostid trilobites that lived during the final Lower Cambrian and the Middle Cambrian. They are small or very small, and have a thorax of two or three segments. Eodiscidae includes nine genera.

Cedaria is a small, rather flat trilobite with an oval outline, a headshield and tailshield of approximately the same size, 7 articulating segments in the middle part of the body and spines at the back edges of the headshield that reach halflength of the body. Cedaria lived during the early part of the Upper Cambrian (Dresbachian), and is especially abundant in the Weeks Formation.

References

↑ Available Generic Names for Trilobites P.A. Jell and J.M. Adrain.
↑ Shergold, J.H.; Laurie, J.R. (1997). "Introduction to the Suborder Agnostina". In H.B. Whittington; et al. (eds.). Treatise on Invertebrate Paleontology, Part O., Revised. Vol. 1. Introduction, Order Agnostina, Order Redlichiida. Lawrence, Kansas: University of Kansas/Geological Society of America Inc.
1 2 3 4 Westrop, S,R.; Adrian, J.M.; Landing, E. (2011). "The Cambrian (Sunwaptan, Furongian) agnostoid arthropod lotagnostus Whitehouse, 1936, in Laurentian and Avalonian North America: systematics and biostratigraphic significance" (PDF). Bulletin of Geosciences. 86 (3): 569–594. doi: 10.3140/bull.geosci.1256 . Retrieved 10 June 2013.
↑ Lazarenko, N.P.; Gogin, I.Y.; Pegel, T.V.; Abiamova, G.P. (2011). "The Khos-Nelege River section of the Ogon'or Formation: a potential candidate for the GSSP of Stage 10, Cambrian System" (PDF). Bulletin of Geosciences. 86 (3): 555–568. doi: 10.3140/bull.geosci.1270 . Retrieved 12 June 2013.

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[1] Available Generic Names for Trilobites P.A. Jell and J.M. Adrain.

[2] Shergold, J.H.; Laurie, J.R. (1997). "Introduction to the Suborder Agnostina". In H.B. Whittington; et al. (eds.). Treatise on Invertebrate Paleontology, Part O., Revised. Vol. 1. Introduction, Order Agnostina, Order Redlichiida. Lawrence, Kansas: University of Kansas/Geological Society of America Inc.

[WAL-3] 1 2 3 4 Westrop, S,R.; Adrian, J.M.; Landing, E. (2011). "The Cambrian (Sunwaptan, Furongian) agnostoid arthropod lotagnostus Whitehouse, 1936, in Laurentian and Avalonian North America: systematics and biostratigraphic significance" (PDF). Bulletin of Geosciences. 86 (3): 569–594. doi: 10.3140/bull.geosci.1256 . Retrieved 10 June 2013.

[4] Lazarenko, N.P.; Gogin, I.Y.; Pegel, T.V.; Abiamova, G.P. (2011). "The Khos-Nelege River section of the Ogon'or Formation: a potential candidate for the GSSP of Stage 10, Cambrian System" (PDF). Bulletin of Geosciences. 86 (3): 555–568. doi: 10.3140/bull.geosci.1270 . Retrieved 12 June 2013.

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