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.
- SourceAvailable from: Fabrizio Cecca[Show abstract] [Hide abstract]
ABSTRACT: The potyphytetic suborder Ancyloceratina had an evolutionary success during the entire Cretaceous period Protancyloceratinae appeared in Farly Tithonian and Crioceratitinae during the Late Valanginian-Early Hauterivien transition. Eustatic variations or buoyancy efficiency are not related with the evolutionary success of these two lineages. Their evolution was favored by trophic opportunities created after important, palaeogeographic global changes.RésuméLe sous-ordre polyphylétique des Ancyloceratina a eu un succès évolutif durant toute la périodecrétacée. Les Protancyloceratinae apparaissent au Tithonien inférieur et les Crioceratitinae au passage Valanginien - Hauterivien. Les variations eustatiques et l'efficacité de la flottaison n'ont pas de relation avec le succès évolutif de ces deux lignées. Cette évolution a été favorisée par les opportunités trophiques, créées à la suite d'importants changements paléogéographiques à l'échelle globale.Comptes Rendus de l Académie des Sciences - Series IIA - Earth and Planetary Science 01/1997; 325(8):629-634.
- [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.Paleontological Journal 01/2009; 43(5):527-536. · 0.47 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Previous analyses of ammonite functional morphology have assumed that the animal filled the entire body chamber, and that movement of the animal (such as withdrawal of the head and arms into the shell) had little effect on orientation. An alternative anatomy is proposed here: the ammonite animal was small, mobile, and capable of moving away from the aperture when threatened. The effect of this anatomy on the hydrostatics of aspinoconic, ancycloconic, and hamiticonic heteromorph ammonites is analysed. This analysis suggests that movement of the body would significantly alter the distribution of mass and hence orientation.01/1998;