Variability of Relative Body Chamber Length in Jurassic Ammonites of the Family Cardioceratidae Siemiradzki, 1891, and Its Taxonomic Significance

Resumo

Analysis of the variability of the angular length of the body chamber in the subfamilies Arctocephalitinae and Cadoceratinae (family Cardioceratidae) has shown that this feature is extremely variable both at the species level and within the genus. For most taxa the length of the body chamber (either fixed values, or mean statistical values) has no identification significance. Estimates of high variability of the body chamber length allow some classification systems of early cardioceratids to be critically evaluated and some concepts of the theoretical shell morphology and paleobiology of ammonites to be reassessed. This is primarily based on models, in which the length of the body chamber coincides with the length of the soft body, and so indirectly influences shell hydrodynamics and hydrostatics, as well as ammonite locomotion and life style. High variability of the body chamber length suggests that this effect was not as significant as previously thought.