Middle Cambrian fossils from Tizi N'Tichka, the High Atlas, Morocco. Part 2. Hyolitha

Ladislav, Marek; Malinsky, John M.; Geyer, Gerd

doi:10.1017/s0022336000040129

Cited by 24 publications

(8 citation statements)

References 18 publications

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“…The operculum of Contitheca chrosniaki Marek et al . () from the middle Cambrian of Morocco has similar proportions but is more flattened ventrally, with a fan of weakly expressed folds and furrows opening from the initial growth stage towards the ventral margin. Orthothecid operculum A lacks the prominent folds and concave ventral margin of Decoritheca ?…”

Section: Hyolithellus Sp Figure T Y–aamentioning

confidence: 95%

The Buen Formation (Cambrian Series 2) biota of North Greenland

Peel

Willman

2018

Papers in Palaeontology

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The diverse metazoan fauna from the upper member of the Buen Formation of North Greenland is described as a complement to published descriptions of the exceptionally preserved fauna of the Sirius Passet Lagerstätte which occurs in the lowest beds of the formation. Considered together with organic‐walled microfossils, which are absent from the Sirius Passet Lagerstätte on account of regional metamorphism, the fauna from the upper member provides an extended picture of the Buen Formation biota (Cambrian, Series 2, Stages 3–4; Montezuman–Dyeran of Laurentian usage). Although dominated numerically by specimens of the olenelline trilobites Limniphacos and Mesolenellus, the oldest assemblages (Montezuma–Dyeran boundary) from the upper member of the Buen Formation are characterized by a high diversity of hyoliths which often occur as partial associations of conch, operculum and helens in the dark mudstones; hyoliths are rare in the Sirius Passet Lagerstätte. Sponges are rare in the upper Buen Formation but diverse at Sirius Passet. Unlike the Sirius Passet Lagerstätte, fossil remains of non‐mineralized metazoans with limbs and other details of internal anatomy do not occur in the upper Buen Formation, although organic tubes assigned to a new selkirkiid stem group priapulid (Sullulika) are common. New taxa: Alutella siku sp. nov., Sullulika broenlundi gen. et sp. nov., Nevadotheca boerglumensis sp. nov., Kalaallitia myliuserichseni gen. et sp. nov., Nasaaraqia hyptiotheciformis gen. et sp. nov., Trapezovitus malinkyi sp. nov., Decoritheca? hageni sp. nov.

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Section: Hyolithellus Sp Figure T Y–aamentioning

confidence: 95%

The Buen Formation (Cambrian Series 2) biota of North Greenland

Peel

Willman

2018

Papers in Palaeontology

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“…The radial ridges or crenulations are unusual amongst hyolith opercula, but are somewhat reminiscent of those in Slapylites Marek, (Marek ; Marek et al . ; Malinky & Berg‐Madsen ; Peel et al . ; Valent et al .…”

Section: Resultsmentioning

confidence: 99%

Plywood‐like shell microstructures in hyoliths from the middle Cambrian (Drumian) Gowers Formation, Georgina Basin, Australia

Moore

Porter

2018

Palaeontology

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Hyoliths are a group of Palaeozoic fossils with calcareous shells whose affinities remain controversial. As their shells were originally aragonitic, their fossils are usually coarsely recrystallized, and few data on their microstructure are available. We report hyoliths from the middle Cambrian (Drumian, Floran) Gowers Formation of the eastern Georgina Basin, Queensland. These are preserved as phosphatic internal moulds, often with the inner layers of the shell also partly replaced by phosphate. Microstructural details preserved by this early diagenetic phosphatization show that these hyolith conchs were originally composed of fibrous crystallites, c. 0.5 μm wide, parallel to one another and to the inner surface of the shell. In several species, the fibres are arranged in a plywood‐like structure composed of multiple lamellae with a different fibre orientation in each lamella: often they are transversely oriented (relative to the long axis of the conch) in the inner part of the wall and longitudinally oriented in the outer part. Opercula also show a microstructure of parallel fibres. The lamello‐fibrillar microstructure we report from hyoliths is reminiscent of microstructures of many Cambrian molluscs; that this microstructure is found in both conchs and opercula suggests that these structures are serial homologues of one another, and in this respect they resemble brachiopod valves. As with many other biological plywoods, the hyolith shell probably records self‐organization in a liquid‐crystal‐like organic matrix. This provided a straightforward way to construct a material that could resist stresses from different directions, offering an effective defence against predators.

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“…Mineralized helens are uncommon in the fossil record (Walcott 1890 a , b ; Poulsen 1967; Yochelson 1974; Marek et al . 1997 a ); helens preserved as carbonaceous films are somewhat more abundant (e.g.…”

Section: Methodsmentioning

confidence: 99%

Skeletal Microstructure of Helens, Lateral Spines of Hyolithids

Mus¹,

Bergström²

2007

Palaeontology

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In hyolithids the skeleton consists of four elements: a conch, an operculum and a pair of long, logarithmically curved 'spines' called helens. These last elements are rarely preserved, and have therefore remained poorly known and enigmatic. We have studied three-dimensionally preserved helens of the species 'Hyolithes' lanceolatus, from the Permian of New South Wales, Australia, and 'Hyolithes' groenwalli, from the Cambrian of Bornholm, Denmark. Helens were massive calcareous elements. Their original microstructure, herein reported for the first time, consisted of concentric lamellae surrounding a narrow elongated core, which may have been rich in organic matter. This concentric pattern resulted from the successive accretion of shell material at the proximal, internal portion of helens. This growth model is in accordance with helen morphology and with the presence of a characteristic surface sculpture of overlapping lamellae.

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Middle Cambrian fossils from Tizi N'Tichka, the High Atlas, Morocco. Part 2. Hyolitha

Cited by 24 publications

References 18 publications

The Buen Formation (Cambrian Series 2) biota of North Greenland

The Buen Formation (Cambrian Series 2) biota of North Greenland

Plywood‐like shell microstructures in hyoliths from the middle Cambrian (Drumian) Gowers Formation, Georgina Basin, Australia

Skeletal Microstructure of Helens, Lateral Spines of Hyolithids

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