Theoretical Modeling of Ammonoid Morphology

Okamoto, Takashi

doi:10.1007/978-1-4757-9153-2_8

Cited by 46 publications

(56 citation statements)

References 23 publications

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“…Whorl expansion rate/body chamber length diagrams of six representative ammonoid genera of late Emsian and Eifelian age. The broad grey-shaded curve is based on a diagram from Okamoto (1996) and own data. The width of the curve is supposed to indicate the primary variability of these parameters.…”

Section: Mimagoniatitoideamentioning

confidence: 99%

Life-cycles of some Devonian ammonoids

Klug¹

2001

Lethaia

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Whorl expansion rates of six representative ammonoid genera from late Emsian and Eifelian strata of Morocco were calculated for each whorl. The corresponding body chamber lengths and the orientations of the apertures were computed based on these values. The resulting body chamber length and orientation of the aperture graphs were compared with other conch features, ecology of Recent cephalopods, and sedimentological data of the host rocks in the Ta lalt (eastern Anti-Atlas, Morocco). A subdivision of the ontogeny of these ammonoids was achieved comprising the early and late embryonic periods, the juvenile period, the preadult, and the adult growth period. All growth periods are de ned by speci c changes in growth, conch morphology, and mode of life. According to this reconstruction, hatchlings were probably already capable of active movements. Differentiation in two main modes of life of the examined taxa occurred in the late juvenile or early preadult period. As preadult animals, most of the Mimagoniatitoidea and Agoniatitoidea became active swimmers (Nektonic), whereas the representatives of the Anarcestoidea were capable of slow movements only (Planktonic). As adults, most representatives of the three superfamilies had an approximately horizontally oriented aperture, allowing active swimming and possibly active choice of spawning sites. Additionally, the new ammonoid taxon Rherisites tuba gen. nov., sp. nov. from the late Emsian is introduced. & Ammonoidea, Emsian, Eifelian, Morocco, ontogeny, palaeoecology.

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Section: Mimagoniatitoideamentioning

confidence: 99%

Life-cycles of some Devonian ammonoids

Klug¹

2001

Lethaia

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“…Therefore, the BCL has to be calculated indirectly in most cases. Okamoto (1996) has found a correlation between whorl expansion rate (WER) and BCL of some Mesozoic ammonoids and Recent Nautilus. Accordingly, several values of BCL from the literature (Chlupa Âc Ï and Turek 1983) and additional values of Moroccan ammonoids were used to produce a corresponding graph for Devonian ammonoids (Klug 2001b;Text-®g.…”

Section: B O D Y C H a M B E R L E N G T H A N D O R I E N T A T I O mentioning

confidence: 99%

“…5. Diameter/whorl expansion rate diagram (bottom left), body chamber length/whorl expansion rate diagram (bottom right, modi®ed afterOkamoto 1996), and body chamber length/orientation of the aperture diagram (top, modi®ed after Saunders and Shapiro 1986) with values for the Pinacitinae. The width of the curves in the latter two diagrams (right) schematically indicates the variability of the correlation between the parameters.…”

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Occluded Umbilicus In The Pinacitinae (Devonian) And Its Palaeoecological Implications

Klug

Korn

2002

Palaeontology

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with preserved shell structures from the eastern Anti-Atlas (Morocco) have revealed unusual morphological features. The Pinacitinae belong to the earliest ammonoids which closed their umbilici. As an approach to an interpretation of these structures, the representatives of the subfamily Pinacitinae (Exopinacites singularis, Pinacites jugleri, P. eminens) are compared with other ammonoids, e.g. Acrimeroceras, Araucanites, Clistoceras, Gaudryceras, Nathorstites, Prolobites, and Synpharciceras, which produced umbilical plugs and covers. Some of these are comparable in structure to Nautilus pompilius and N. belauensis. In contrast to all of these taxa, the lateral shell wall of the Pinacitinae reached the centre of the umbilicus and formed an umbilical lid. The umbilical shell wall rests on the umbilical lid of the previous whorl. This construction probably had the advantage that it improved the hydrodynamic properties of the conch, along with the oxyconic conch shape and the approximately horizontal orientation of the aperture.

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“…5-8) of whorls. Such forms have relatively short but high body chambers, whereas ammonoids with a low WER have long but flattened body chambers (Okamoto 1996;Klug and Korn 2002). Individuals that have a high CWI possess conchs that are rather globular in appearance, and those conchs with a low CWI, are discoidal.…”

Section: Origin Of the Ammonoidea And Early Diversificationmentioning

confidence: 99%

Taxonomic Diversity and Morphological Disparity of Paleozoic Ammonoids

Korn

Klug

Walton

2015

Topics in Geobiology

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The Ammonoidea are well represented in terms of numbers of species over a large range of time and they have survived many extinction events. The time interval from the Early Devonian through to the Triassic has seen ammonoid groups evolve and become extinct. The evolutionary history of the Paleozoic ammonoids was punctuated by some extinction events with near extinction events and subsequent recoveries. A Principal Components Analysis (PCA) based on the conch width index (CWI), umbilical width index (UWI) and whorl expansion rate (WER) parameters from 4834 ammonoid species of Devonian to Triassic age produced an empirical morphospace this time interval. The morphospace of Paleozoic ammonoids shows some subtle changes between the periods, but generally, the occupied area is remarkably similar.

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Theoretical Modeling of Ammonoid Morphology

Cited by 46 publications

References 23 publications

Life-cycles of some Devonian ammonoids

Life-cycles of some Devonian ammonoids

Occluded Umbilicus In The Pinacitinae (Devonian) And Its Palaeoecological Implications

Taxonomic Diversity and Morphological Disparity of Paleozoic Ammonoids

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