Since the last review of Jurassic—Cretaceous ammonoid ecology (Westermann, 1990), much additional work has been done on ammonoid autecology (architecture or macrostructure) as well as on the associations and occurrences of ammonoids in the field (synecology). Important works on Paleozoic through Triassic ammonoids, dispersed in the literature, have not been reviewed previously. Quantitative autecological studies, begun in the mid-1980s, concerned buoyancy and orientation. Electron and light microscopic studies of the shells have also contributed to an understanding of the soft parts. Research on shell fabrication, strength, and hydrodynamics has increased greatly, also contributing to ammonoid autecology. Intraspecific morphological variation has been studied intensively but remains poorly understood ecologically; most authors still fail to consider variation in the functional interpretation of shell shape. Ammonoid synecology was significantly advanced in recent years by the renewed interest in Paleozoic and Mesozoic dysoxic black-shale facies and their relation to eustasy and orbitally enforced cycles. Other recent studies in synecology have emphasized the interrelations among sediment, eustasy, and biofacies. Finally, ammonoid taxonomy has been summarized in The Ammonoidea (Special Volume 18, The Systematics Association, 1981).

Ammonoid Life and Habitat

Die Arbeit behandelt die fruhontogenetische Mollusken-Entwicklung der Schale und der diese bildenden Epithelien. Speziell werden Archaeogastropoden, Ammoniten und Neritaceen behandelt und mit einigen ausgewahlten hoheren Gastropoden verglichen, Archaeogastropoden, Neritaceen und hohere Gastropoden sind palaontologisch gut trennbare Gruppen, wenn die Bildung und Morphologie der fruhontogenetischen Schalen verglichen werden. Eine Verbindung zwischen Archaeogastropoden und Ammoniten zeigt sich in der Art der Mineralisierung der organischen Primarschalchen. Cephalopoden sind generell eine ziemlich einheitliche Gruppe der Mollusken, deren Vorfahren den Vorfahren der Archaeogastropoden nahe verwandt waren. Neritaceen und hohere Schnecken verbindet die innere Befruchtung sowie der Besitz einer echten Larve, die den Archaeogastropoden wie auch den Cephalopoden fehlt. Die Ergebnisse werden in einem Schema des Entwicklungsablaufes in der Ontogenese dargestellt und zur Phylogenese des Molluskenstammes in Bezug gebracht. Hierzu werden auch einige Entwicklungsablaufe bei Kaferschnecken, Muscheln und Scaphopoden miteinbezogen. Es erweist sich, das einige in der Systematik bisher noch bewertete Eigenschaften und Merkmale nur sehr mit Vorsicht genutzt werden durfen, wahrend andere bisher wenig beachtete Kriterien mehr Aussagekraft besitzen als bisher vermutet. Die Bildung der Schalendruse erweist sich als die zentrale Erfindung der Mollusken, die vermutlich wahrend des oberen Kambriums die Conchifera entstehen lies. Mit vielen Beispielen wird belegt, das innerhalb aller behandelten Molluskengruppen eine Ausdeutung fossiler Schalenreste nur dann zu sinnvollen Ergebnissen fuhrt, wenn die Bildungsweise der Schale bei rezenten Verwandten gut untersucht ist. Umgekehrt zeigt es sich, das Modelle der Evolution der Mollusken, die nur auf Rezentbefunden basieren, in der Regel wenig Ahnlichkeit mit dem tatsachlichen Ablauf der Geschehnisse aufweisen.

Morphologie und Bildung der fruhontogenetischen Gehause bei conchiferen Mollusken.

During the Devonian Nekton Revolution, ammonoids show a progressive coiling of their shell just like many other pelagic mollusk groups. These now extinct, externally shelled cephalopods derived from bactritoid cephalopods with a straight shell in the Early Devonian. During the Devonian, evolutionary trends toward tighter coiling and a size reduction occurred in ammonoid embryonic shells. In at least three lineages, descendants with a closed umbilicus evolved convergently from forms with an opening in the first whorl (umbilical window). Other lineages having representatives with open umbilici became extinct around important Devonian events whereas only those with more tightly coiled embryonic shells survived. This change was accompanied by an evolutionary trend in shape of the initial chamber, but no clear trend in its size. The fact that several ammonoid lineages independently reduced and closed the umbilical window more or less synchronously indicates that common driving factors were involved. A trend in size decrease of the embryos as well as the concurrent increase in adult size in some lineages likely reflects a fundamental change in reproductive strategies toward a higher fecundity early in the evolutionary history of ammonoids. This might have played an important role in their subsequent success as well as in their demise.

Early evolutionary trends in ammonoid embryonic development

The current knowledge about the ammonoid/habitat relation is reviewed and in part newly interpreted. The autecology of ammonoids, such as ontogeny and habitat, based on morphological and geochemical analyses in association with results from modern relatives, forms the foundation for subsequent interpretations. Synecological interactions (predator-prey, infestation) are discussed with reference to sedimentary facies and the corresponding biofacies. Arguments for a possible mode of life and habitat are given based on the modern data on the food/prey habits and predation habitats of ammonoids. The state of the art in scientific investigations on ammonoid life and habitat is summarized, reviewed and in part reinterpreted. Traditional assumptions based on facies analyses are strengthened or contradicted by more recent methods such as morphospace and stable isotope analyses. Not yet tested hypotheses, speculations and mathematical models are tested by comparing the results with new geophysical data.

Ammonoid Habitats and Life History

2 – Main Features of Cephalopod Evolution

Carboniferous and Permian Bactritoidea (Cephalopoda) in North America

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Carboniferous and Permian Bactritoidea (Cephalopoda) in North America