Orthoconic cephalopods and associated fauna from the late Ordovician Soom Shale <i>Lagersta¨tte</i>, South Africa

Gabbott, Sarah E.

doi:10.1111/1475-4983.00065

Cited by 60 publications

(68 citation statements)

References 18 publications

(36 reference statements)

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“…Affinity of some Early Palaeozoic straight-shelled cephalopods to coleoids has been already indicated, espe- cially by finds in orthocerids of coleoid type of radula (Mehl 1984, Gabbot 1999; reported traces of ten tentacles (Flower 1955b, Stürmer 1985 has been, however, doubted. A "semi-internal" shell of Sphooceras temporarily completely encased by soft tissue, reduction of the length of the phragmocone, shortening of the shell accompanied by relative prolongation of body chamber possessing oblique aperture, dorsally situated retractor muscle imprints, probably very small subglobular protoconch lacking cicatrix, noncalcified connecting rings and hydrodynamic shape of the shell are all features, which evolved in the genus Sphooceras in convergence to the Angusteradulata.…”

Section: Discussionmentioning

confidence: 99%

“…The possibility of negative buoyancy and a benthic mode of life of orthocerids was proposed by Ebel (1999), but has not been widely accepted. Some straight-shelled cephalopods, however, possess some very progressive features, similar to coleoids (for summary see Mehl 1984, Engeser 1996, Gabbot 1999. The question remains, whether the mechanism of swimming in these cephalopods was the same as in the Recent Nautilus.…”

Section: Ecology Of Sphoocerasmentioning

confidence: 99%

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"An endocochleate experiment" in the Silurian straight-shelled cephalopod Sphooceras

Turek¹,

Manda²

2012

Bull. Geosci.

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Sphooceras truncatum (Barrande, 1860), a Silurian straight-shelled cephalopod with a short finger-shaped shell, is one of a few cephalopods in which natural truncation of the apical part of the phragmocone from the rest of the conch is confirmed. Periodic natural removal of the apical part of the shell (4 to 5 phragmocone chambers) preceded formation of a terminal callus and a calcareous plug closing the septal foramen. The apical callus probably originated by fusion of the truncation septum with episeptal deposits. These structures temporarily formed the new apex on which two additional calcareous layers had been secreted. A unique specimen preserves a colour pattern in the convex apical region, which proves that the shell in Sphooceras was temporarily completely surrounded by mantle extending from the body chamber, i.e. the cephalopod was at least temporarily endocochleate. The co-occurrence of different growth stages of S. truncatum together with one type of short juvenile orthoceracone shell, with a maximum of eight phragmocone chambers and a very small subglobular initial chamber indicates that these embryonic shells may belong to Sphooceras. Two other genera are discussed, both previously included in the family Sphooceratidae: Disjunctoceras Gnoli in Kiselev, 1992 and Andigenoceras Gnoli in Kiselev, 1992. The newly discovered thickening of the apex in "Disjunctoceras" disjunctum, the type species of Disjunctoceras, indicates that this species does not differ substantially from Sphooceras and should be reassigned to this genus. Similarly, representatives of Andigenoceras also possess characteristic features of Sphooceras. Sphooceras has many features characteristic for modern cephalopods: short, thin-walled, semi-internal shell; phragmocone reduced to only a few chambers; uncalcified connecting rings; apical callus (a structure analogous to the belemnite rostrum); retractor muscle scars situated dorsally; very small protoconch without cicatrix. In some exceptionally well-preserved cephalopods with orthoceracone shell radula with seven rows of teeth were observed. All these features support the thesis that some straight-shelled cephalopods are evolutionarily closer to coleoids than nautiloids and their separation from nautiloids is legitimate. Vascular imprints on the surface of the cameral deposits provide further support for their primary origin and the existence of a cameral mantle. The character of cameral deposits in Sphooceras demonstrates that the systematic value of these structures in other straight-shelled cephalopods, a subject of controversy, has limited value. The morphology of Sphooceras also demonstrates that the boundary between endocochleate and ectocochleate cephalopods is not sharp, i.e. internalisation of the shell in cephalopods occurred repeatedly.•

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Section: Discussionmentioning

confidence: 99%

Section: Ecology Of Sphoocerasmentioning

confidence: 99%

"An endocochleate experiment" in the Silurian straight-shelled cephalopod Sphooceras

Turek¹,

Manda²

2012

Bull. Geosci.

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“…Since the Ordovician, the fossil record has included discinids attached to brachiopods (Cooper 1956, Bassett et al 2009), bivalves (Davidson 1888), cephalopods (Havlí-ček 1972, Lockley & Antia 1980, Gabbott 1999, conulariids (Mergl 2006), plant debris (Thomson 1971) and chondrophorans (Richards 1974, Hannibal 2003. Observations of Recent discinids indicate a cryptic mode of life on the underside of cobbles (Paine 1962) or even an infaunal mode of life on the underside of large boulders deeply embedded in coarse sand (Kato 1996).…”

Section: Discussionmentioning

confidence: 99%

Discinid brachiopod life assemblages, fossil and extant

Mergl¹

2010

Bull. Geosci.

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Clusters of discinid brachiopod shells observed in Devonian and Carboniferous strata are interpreted as original life assemblages. The clusters consist of Gigadiscina lessardi (from Algeria), Oehlertella tarutensis (from Libya), Orbiculoidea bulla and O. nitida (both from England). Grape-like clusters of the Recent species Discinisca lamellosa and D. laevis are described and their spacing and size-frequency distribution are discussed. The possible function of clustering as protection against grazing pressure is suggested.•

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“…The specimens preserve a possible stomach and an unambiguous radula, which consists of up to 26 transverse rows with five simple tooth-like elements in each row (Gabbott 1999). Radulae are a key synapomorphy of the Mollusca and provide important phylogenetic and ecological information, but they are rarely preserved.…”

Section: Molluscsmentioning

confidence: 99%

The late Ordovician Soom Shale Lagerstätte: an extraordinary post-glacial fossil and sedimentary record

Gabbott

Browning

Theron

et al. 2016

JGS

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Fossils of the Late Ordovician Soom Shale Lagerstätte are characterized by exceptional preservation of their soft tissues in clay minerals. The low-diversity community lived in an unusual cold-water setting, dominated by anoxic bottom waters, in the immediate aftermath of the Hirnantian glaciation. Giant conodonts represented by complete tooth sets, and one with trunk musculature and liver preserved, unarmoured jawless fish, lobopods and enigmatic taxa are some of the more important fossils. Furthermore, this Lagerstätte also preserves biomineralized Ordovician taxa such as brachiopods, orthoconic nautiloids and trilobites. It is important in capturing the only known examples of many taxa, extending temporal ranges of others and providing a unique glimpse of a post-glacial refugium, at a time when other Lagerstätten are unknown.

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Orthoconic cephalopods and associated fauna from the late Ordovician Soom Shale Lagersta¨tte, South Africa

Cited by 60 publications

References 18 publications

"An endocochleate experiment" in the Silurian straight-shelled cephalopod Sphooceras

"An endocochleate experiment" in the Silurian straight-shelled cephalopod Sphooceras

Discinid brachiopod life assemblages, fossil and extant

The late Ordovician Soom Shale Lagerstätte: an extraordinary post-glacial fossil and sedimentary record

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