Nautiloids of the Paleozoic

Flower, Rousseau H.

doi:10.1130/mem67v2-p829

Cited by 29 publications

(26 citation statements)

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“…Cephalopods with straight shells have been considered to have been active swimmers (Flower 1957, Teichert 1964, but according to some recent views (Mutvei 2002) the dorsal position of their muscle scars shows that their swimming ability was weak, possibly even indicating a planktonic lifestyle (Mutvei 2002, Kröger et al 2005, Klug et al 2010. The possibility of negative buoyancy and a benthic mode of life of orthocerids was proposed by Ebel (1999), but has not been widely accepted.…”

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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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: Ecology Of Sphoocerasmentioning

confidence: 99%

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

Turek¹,

Manda²

2012

Bull. Geosci.

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“…Actinoceratids especially inhabited warm-water carbonate platforms. Actinocerid cephalopods have been interpreted as indicators of tropical and temperate water masses (Flower 1957), but some actinocerids are also known from higher latitudes (Serpagli & Gnoli 1977, Kröger 2008. The actinoceratids are rare in the Wenlock and Ludlow strata of Bohemia, but in the Přídolí, their diversity distinctly increased, but only one species is known from the Lochkovian.…”

Section: Nektobenthic Early Stage and Nektobenthic-benthic Adult (Actmentioning

confidence: 99%

“…Maximal shell diameter in this stage is about 180 mm. According to Flower (1957) and Gnoli (1987), all of the above-mentioned stages were probably nektobenthic with the shell orientated horizontally (cameral deposits); the distinct hyponomic sinus indicates active swimming and jet propulsion. Shells of the first and early-late second stages occur in shallow water facies.…”

Section: Nektobenthic Early Stage With Nektic-nektobenthic Adults (Psmentioning

confidence: 99%

“…Cephalopods placed in this group have a straight adult shell and well developed cameral deposits. According to Flower (1957), the cameral deposits functioned as a counterweight, helping to orient their shell horizontally during life. In some species, the siphuncle was even open in the distal part of the phragmocone, connecting phragmocone chambers with the siphuncle (see Kolebaba 1999Kolebaba , 2002.…”

Section: Nektonic Forms With a Pelagic Early Stagementioning

confidence: 99%

“…Maximal shell diameter was about 20 mm. The above-described shell morphlogy was interpreted as an adaptation for active swimming, resembling that of some coleoids (see Flower 1957).…”

Section: Nektonic Forms With a Pelagic Early Stagementioning

confidence: 99%

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Silurian-Devonian boundary events and their influence on cephalopod evolution: evolutionary significance of cephalopod egg size during mass extinctions

Manda¹,

Frýda²

2010

Bull. Geosci.

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Diversity evolution of 197 of the latest Ludlow-Lochkovian cephalopod species from Bohemia (representing more that 70 percent of all species known worldwide) was analysed and compared with changes in the global carbon cycle in the marine ecosystem. Our results show a distinct relationship between cephalopod species diversity and the global carbon cycle. A progressive increase in δ 13 C values in marine carbonates from the Monograptus lochkoviensis Zone to the end of the Monograptus transgrediens Zone reflects an increase of bioproductivity in the marine ecosystem. This increase was probably caused by a shallowing of the upwelling system, thus importing nutrient-rich water. A progressive cooling during the Přídolí and earliest Lochkovian triggered these changes in the upwelling system. Our data also show an increase in total diversity of cephalopod species, which may be explained by greater availability of new food sources for a period corresponding to the progressive increase in δ 13 C values. In the latest Silurian, δ 13 C reached its maximal values while the Lochkovian is characterized by steady conditions with a decreasing tendency in δ 13 C values. Strong, selective extinction started in the latest Silurian Monograptus transgrediens Zone and continued to the earliest Devonian Monograptus uniformis Zone. This extinction affected benthic and demersal cephalopod species with relatively large eggs and long incubation times. The change in dynamics of the global carbon cycle thus coincides with the beginning of this extinction. An anoxic or hypoxic event in the period between the LAD Monograptus transgrediens Zone (Transgrediens Event) in the latest Přídolí and the base of the Devonian Monograptus uniformis Zone (documented also from offshore sequences from Poland) is considered to be a cause for the extinction of non-pelagic cephalopods. Our study also revealed a need to revise and define all earlier established bioevents in the Silurian-Devonian boundary interval more clearly. •

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Gigantism, taphonomy and palaeoecology of Basiloceras, a new oncocerid genus from the Middle Devonian of the Tafilalt (Morocco)

2019

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The genus Basiloceras gen. nov. containing the two species B. goliath sp. nov. and B. david sp. nov. is described. It belongs to the Acleistoceratidae within the Oncocerida. Both species are from the Middle Devonian of the Tafilalt (Morocco). The genus exhibits a large interspecific size range between the small Eifelian B. david sp. nov. and the Givetian B. goliath sp. nov., the largest Devonian oncocerid currently known, altogether only second to some fragmentary remains of Calchasiceras from the Carboniferous of Russia. Several other large species are mainly known from the late Emsian of Bohemia and the Eifelian of Germany. The holotype of B. goliath sp. nov. contains numerous epicoles, trace fossils and shell debris, which are discussed in the context of its taphonomy. Compared to other oncocerids, Basiloceras is characterised by a short body chamber, which might be related to buoyancy regulation. In contrast to some older publications, we do not regard breviconic oncocerids with contracted aperture as benthic or nektobenthic animals, but instead, we think that they dwelled in the water column.

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Nautiloids of the Paleozoic

Cited by 29 publications

References 0 publications

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

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

Silurian-Devonian boundary events and their influence on cephalopod evolution: evolutionary significance of cephalopod egg size during mass extinctions

Gigantism, taphonomy and palaeoecology of Basiloceras, a new oncocerid genus from the Middle Devonian of the Tafilalt (Morocco)

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