Weymouthiidae

Weymouthiidae; Temporal range: Botomian/Delamaran (Olenellus- and Eokochaspis-zones) PreꞒ Ꞓ O S D C P T J K Pg N
	Morocconus , from Morocco
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	† Trilobita (?)
Order:	† Agnostida
Suborder:	† Eodiscida
Family:	† Weymouthiidae ; Kobayashi 1943
Genera
	† Abakolia ; † Acidiscus ; † Acimetopus ; † Analox ; † Bathydiscus ; † Bolboparia ; † Chelediscus ; † Cobboldites ; † Leptochilodiscus ; † Litometopus ; † Mallagnostus ; † Meniscuchus ; † Morocconus ; † Ninadiscus ; † Oodiscus ; † Pseudocobboldia ; † Runcinodiscus ; † Semadiscus ; † Serrodiscus ; † Stigmadiscus ; † Tannudiscus ; † Weymouthia ;
Synonyms [ citation needed ]
	†Ladadiscinae;

Last updated August 09, 2024

The Weymouthiidae^[2] are an extinct family of eodiscinid agnostid trilobites. They lived during the late Lower Cambrian and earliest Middle Cambrian (Botomian to Delamaran) in the so-called Olenellus- and Eokochaspis-zones in the former paleocontinents of Laurentia, Avalonia, Gondwana. The Weymouthiidae are all blind and lack free cheeks.

Taxonomy

Ancestors

The Weymouthiidae have developed from a stock within the Hebediscidae.^[3]

Descendants

The Weymouthiidae are a paraphyletic family because the Agnostina suborder is nested within it, particularly in the clade that further consists of the genera Mallagnostus, Chelediscus, Tannudiscus and Jinghediscus.^[4] The trend in the Weymouthiidae to reduce the occipital ring is carried furthest in Chelediscus, Tannudiscus and the Agnostina with the occipital ring divided into basal lobes.^[3]

Description

Most taxa in this family are small (1–2 cm or 0.4–0.8 inches long), but this is large for the Eodiscina. The glabella is wide at its base, normally parallel sided but may taper gently or be at its widest at half length. Glabellar furrows are mainly absent, but incomplete furrows may be present in some species and deeply impressed transglabellar furrows also occur. Free cheeks (or fixigenae) are normally confluent in front of glabella. The occipital ring may be simple or split into two lateral lobes (e. g. in Chelediscus and Tannudiscus). All Weymouthiidae lack eyes. The thorax consists of three rings when known (Mallagnostus, Marocconus, Serrodiscus, Tannudiscus and Weymouthia). The pygidial axis is long and strongly tapered with 10 or more axial rings. The segmentation of the axis, however, is often effaced. The Weymouthiidae include forms with the rear of the glabella roundly expanded over the occipital ring or with a vertical spine, forms in which the occipital ring cannot be discerned because the glabella is expanded, and forms with a primitive occipital structure but with a greatly increased numbers of axial segments.^[3]

Related Research Articles

Paradoxides is a genus of large to very large trilobite found throughout the world during the Middle Cambrian period. One record-breaking specimen of Paradoxides davidis, described by John William Salter in 1863, is 37 cm (15 in). The cephalon was semicircular with free cheeks ending in long, narrow, recurved spines. Eyes were crescent shaped providing an almost 360° view, but only in the horizontal plane. Its elongate thorax was composed of 19–21 segments and adorned with longish, recurved pleural spines. Its pygidium was comparatively small. Paradoxides is a characteristic Middle-Cambrian trilobite of the 'Atlantic' (Avalonian) fauna. Avalonian rocks were deposited near a small continent called Avalonia in the Paleozoic Iapetus Ocean. Avalonian beds are now in a narrow strip along the East Coast of North America, and in Europe.

Agnostus is a genus of agnostid trilobites, 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 2⁄3× 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.

Acidiscus Rasetti, 1966, is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi T. (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.

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.

Ninadiscus Korobov, 1980, 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 the base of the Middle Cambrian, the Miaolingian Series and Wuliuan Stage.

Meniscuchus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Botomian stage, which lasted from approximately 522 to 516 million years ago. This faunal stage was part of the Cambrian Period. Meniscuchus has been found in the USA, Canada, Russia and Australia.

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, 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.

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.

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.

Mallagnostus Howell, 1935, is a trilobite genus belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida Salter (1864) according to Whittington et al. 1997. It lived during the late Lower Cambrian, with remains found in USA, Canada (Newfoundland), Spain, England, Russia, Mongolia, and the early Middle Cambrian as reported from China and Russia (Yakutia).

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.

Delgadella is a diminutive trilobite that lived during the late Lower Cambrian and has been found in Russia, Mongolia, Spain, Italy (Sardinia), Portugal, Morocco and Canada (Newfoundland). It can be recognized by its strongly effaced headshield and tailshield, with narrow but distinct furrows and borders along its margins, and three thorax segments.

Pliomera is a genus of trilobites that lived during the Middle Ordovician on the paleocontinent Baltica, now Norway, Sweden, Estonia and the Russian Federation, and in Argentina. It can be recognized for its pentagonal glabella widest between the frontal corners, with an inverted V-shaped occipital ring. In front of the occipital furrow that crosses the entire glabella, two pairs of dead-ending furrows create three side lobes left and right. The front of the glabella also has three dead-ending furrows, a very short one on the midline and left and right a longer one, directed inward and slightly backward. The eyes are small and are not connected to the glabella by an eye ridge. The thorax and pygidium are very regularly divided into up to 23 rather narrow segments, without a furrow within each of the pleurae. The pleurae are clearly wider than the axis. The pygidium ends in downward pointing toothlike spines.

Tannudiscus Pokrovskaya (1959) is a genus of Eodiscinid trilobites belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida. It lived during the late Lower Cambrian, with remains found in Canada (Newfoundland), China (Gansu), The United Kingdom (England), and the Russian Federation.

The Hebediscidae Kobayashi, 1944, are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian. They are small or very small, and have a thorax of two or three segments. The Hebediscidae include five genera.

The Calodiscidae Kobayashi, 1943 [nom. transl. Öpik, 1975 ex Calodiscinae Kobayashi, 1943] are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian. They are small or very small, and have a thorax of two or three segments. The Calodiscidae includes five genera.

Tricrepicephalus is an extinct genus of ptychopariid trilobites of the family Tricrepicephalidae with species of average size. Its species lived from 501 to 497 million years ago during the Dresbachian faunal stage of the late Cambrian Period. Fossils of Tricrepicephalus are widespread in Late Cambrian deposits in North America, but is also known from one location in South America. Tricrepicephalus has an inverted egg-shaped exoskeleton, with three characteristic pits in the fold that parallels the margin of the headshield just in front of the central raised area. The articulating middle part of the body has 12 segments and the tailshield carries two long, tubular, curved pygidial spines that are reminiscent of earwig's pincers that rise backwards from the plain of the body at approximately 30°.

References

↑ "PBDB Taxon".
↑ KOBAYASHI T. 1943. Brief notes on the Eodiscids 1, their classification with a description of a new species and a new variety, Proceedings of the Imperial Academy, Tokyo, Volume 19, pp. 37–42.
1 2 3 WHITTINGTON, H. B. et al., Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997
↑ Sam Gon III. "The Relationship of Agnostina to Eodiscina" . Retrieved 18 December 2012.

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[1] "PBDB Taxon".

[2] KOBAYASHI T. 1943. Brief notes on the Eodiscids 1, their classification with a description of a new species and a new variety, Proceedings of the Imperial Academy, Tokyo, Volume 19, pp. 37–42.

[Treatise-3] 1 2 3 WHITTINGTON, H. B. et al., Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997

[4] Sam Gon III. "The Relationship of Agnostina to Eodiscina" . Retrieved 18 December 2012.

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Weymouthiidae Temporal range: Botomian/Delamaran (Olenellus- and Eokochaspis-zones) PreꞒ Ꞓ O S D C P T J K Pg N

Morocconus , from Morocco
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	† Trilobita (?)
Order:	† Agnostida
Suborder:	† Eodiscida
Family:	† Weymouthiidae Kobayashi 1943
Genera^[1]
† Abakolia † Acidiscus † Acimetopus † Analox † Bathydiscus † Bolboparia † Chelediscus † Cobboldites † Leptochilodiscus † Litometopus † Mallagnostus † Meniscuchus † Morocconus † Ninadiscus † Oodiscus † Pseudocobboldia † Runcinodiscus † Semadiscus † Serrodiscus † Stigmadiscus † Tannudiscus † Weymouthia
Synonyms ^{[ citation needed ]}
†Ladadiscinae