Ebel, K. 1992 04 15: Mode of life and soft body shape of heteromorph ammonites. Lethaia, Vol. 25, pp. 179–193. Oslo. ISSN 0024–1164.
Using the idea of a benthic mode of life for ammonites, based on a gastropod-like shell position, it is possible to reconstruct the development of all heteromorph ammonites by regarding single growth stages and the presumable acting forces. The reconstruction of shell formation, particularly the final shell position of heteromorphs with a hook, indicates that the soft body of the ammonite animal was considerably larger than comparison with the present-day Nautilus would suggest.
"Flawed estimates of negative buoyancy and erroneous assumptions about ammonoid growth and soft tissues have led to some extreme interpretations that ammonoids were epibenthic crawlers (e.g. Ebel, 1992). However, it is widely accepted that calculations are in the range of neutral buoyancy (within the limit of estimate ) when making reasonable assumptions (Westermann, 1996; Kröger, 2001). "
[Show abstract][Hide abstract] ABSTRACT: A review of fossil evidence supports a pelagic mode of life (in the water
column) of ammonoids, but they may have spent their life close to the seabottom
(demersal), planktonically, or nektonically depending upon the ontogenetic stage
and taxon. There are good indications for a planktonic mode of life of ammonoid
hatchlings, but a broad range of reproductive strategies might have existed (egglaying,
fecundity). Isotope and biogeographical studies indicate that some forms
migrated or swam for considerable distances, whereas others may have been
primarily transported by oceanic currents during early and/or late ontogeny.
Diverse ammonoid habitats are also supported by evidence from predator–prey
relationships derived from characteristic injuries and exceptional fossil finds,
which indicate chiefly predatory or scavenging lifestyles. Sublethal injuries preserved
in some ammonoid shells, as well as rare stomach and coprolite contents,
provide evidence of predation by other cephalopods, arthropods and various
jawed vertebrates. Various lines of evidence suggest that different groups of
ammonoids had quite different ecologies, but shell shape alone can only give
upper constraints on ammonoid capabilities, a matter that needs to be considered
when interpreting their diversity and evolutionary history.
Journal of Zoology 04/2014; 292(4):229-241. DOI:10.1111/jzo.12118 · 1.88 Impact Factor
"Recently, most authors are inclined to regard most heteromorphs as " semiplanktonic " 2 or megaplanktonic, and to a lesser extent as benthic and nektonic. Note that throughout ontogeny the orientation of the shell, the method of feeding and environmental affinities could have changed (Ward, 1979; Nesis, 1985; Westermann, 1990, 1996; Kakabadze and Sharikadze, 1993; Cecca, 1997, 1998a, 1998b; Westermann and Tsujita, 1999; Lewy, 2002; Baraboshkin and Enson, 2003; Reboulet et al., 2005, etc.), although other opinions (Ebel, 1992, etc.) also exist. "
[Show abstract][Hide abstract] ABSTRACT: The relationship between the appearances of heteromorph and monomorph ammonoids and changes in the abiotic environment was
studied. The correlation of these processes was examined for different intervals in the Early Cretaceous. The phylogeny of
the superfamily Ancyloceratoidea Gill from the time of appearance of early heteromorphs (due to changes in ecological specialization)
and the reversal process of the return to monomorph shells is examined for four superfamilies. The origin of monomorph ammonites
of the superfamilies Theodoritoidea Baraboshkin et I. Michailova, superfam. nov., Douvilleiceratoidea Parona et Bonarelli,
Parahoplitoidea Spath et Deshayesitoidea Stoyanow from heteromorph ancestral families Crioceratitidae Gill, Ancyloceratidae
Gill, Hemihoplitidae Spath, and Heteroceratidae Spath in the superfamily Ancyloceratoidea Gill is suggested.
"A persistent assumption has been that ammonoid shells were designed for resisting ambient hydrostatic pressure, frilled septa being interpreted as complementary structures of reinforcement of the phragmocone against hydrostatic pressure, and complex sutures as evidence of strength demands in shells inhabiting deep habitats (Buckland, 1836; Hewitt, 1993, 1996; Hewitt and Westermann, 1983, 1986, 1987, 1988a, 1988b, 1990, 1997; Jacobs, 1990; Pfaff, 1911; Westermann, 1971, 1973, 1975, 1977, 1982, 1985, 1996; Westermann and Ward, 1980). Other explanations arise from the fields of functional/constructional morphology, physiology, and developmental biology, including the buoyancy control (e.g., fluted septa resulting from inner gas-pressurization counteracting external water pressure, which allowed compression and decompression of a bladder by fleshy-membrane movability (Daniel and others, 1997; Kulicki, 1979; Kulicki and Mutvei, 1988; Saunders, 1995; Seilacher and LaBarbera, 1995; Ward, 1987), maximisation of the connective area of the mantle to the septum or number of muscular insertion points (Ebel, 1992; Henderson, 1984; Seilacher, 1975; Spath, 1919), transportation and storage of cameral fluid (Ward, 1980, 1987), and optimisation of phragmocone shell strength against the point loads such as the teeth of predators (Daniel and others, 1997). It has even been assigned a role in the respiratory process (Newell, 1949). "
[Show abstract][Hide abstract] ABSTRACT: The study of septal patterns in ammonoids has been centered on functional and/or constructional issues. Complexly fluted septa have been considered as complementary structures that reinforce the ammonite shell, their frilled sutures possibly manifesting the demand for strength. Ammonitic sutures display features that denote typical fractal behavior, since they can present very long perimeters relative to the contiguous shell areas, and most provide evidence of statistical self-similarity when observed at varying scales of magnification. However, there is a lower limit of scale measurements below which the fractal behavior of the curve no longer holds, and the perimeter length/step size relationship approaches an Euclidean geometry. This paper describes a new methodology that allows the accurate characterization of suture complexity in ammonoids using the technique of fractal analysis (step-line procedure). The proposed methodology helps to fix the position of this cut-off point, allowing for independent estimates of the fractal dimensions of the curve for both large and small measurement scales (i.e., first and second orders of suture complexity). This approach improves the resolution of fractals in the analysis of suture complexity, thus facilitating the potential interpretation of suture patterns in functional/constructional, evolutionary and paleoecological terms.
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