Mode of life and soft body shape of heteromorph ammonites
ABSTRACT 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.
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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. · 2.04 Impact Factor
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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.Paleontological Journal 01/2009; 43(5):527-536. · 0.47 Impact Factor
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ABSTRACT: Stable isotope (δ18O and δ13C) ratios were measured in successive aragonitic shell sequences of ammonoids (class Cephalopoda) to determine whether their depth distributions changed within ontogeny and whether stable isotope values differ in various morphological groups (e.g. Leiostraca vs. Trachyostraca). We concentrate mainly on δ18O for temperature results and added δ13C data to obtain information on the ontogenetic history, for which full spiral measurements were undertaken for the first time. To obtain valid stable isotope data from ammonoid shells, we measured ontogenetic sequences (full shell) within different genera. Data sets from the Jurassic (Cadoceras) and Cretaceous (Hypacanthoplites, Nowakites) were chosen due to the pure primary aragonitic shell preservation. The study was designed to extract better information on the habitat and life cycle of fossil cephalopods (e.g. ammonoids) in comparison with recent cephalopods (e.g. Nautilus, Spirula, Sepia) possessing equivalent or comparable hard parts. The data from three genera suggest different modes of life in at least two morphological groups.We detected and established two main groups with different ontogenetic strategies based on the δ18O data. The wcw-type (warm–cool–warm type) of Cadoceras resembles strategies in Nautilus and Sepia, which migrate from shallow into deeper environments and back in ontogeny (wc-type, warm–cool-type), and the cw-type (cool–warm type) of Hypacanthoplites resembling the first two migration phases of Spirula (cwc-type), which migrates from deeper into shallower and back again into deeper habitats. The main (three) phases revealed by both δ18O and δ13C data sets most probably reflect diet changes in juvenile to mid-aged individuals, followed by a habitat change for spawning adults. In Cadoceras the temperatures range from 21.2°C for juveniles down to 12.1°C for mid-aged individuals and back up 16.9°C in adults. The cw-type strategy of Hypacanthoplites involves a temperature range of 22.8°C to 28.9°C. The respective mean values are 24.2°C (juveniles), 25.8°C (middle phase) and 27.8°C (adults).The δ13C values also revealed three ontogenetic stages in Cadoceras and Hypacanthoplites, including two major shifts from positive to negative and from negative to positive values, which probably correspond to sexual maturation, the initiation of reproduction, and concomitant changes in diet. The presented data, combined with previous ontogenetic studies (e.g. stable isotopes) on Spirula, Nautilus and Sepia can be used as proxies to directly correlate the habitats and ontogeny of recent and fossil cephalopods.Earth and Planetary Science Letters 01/2010; 296(1):103-114. · 4.72 Impact Factor