Isotope Signature of Ammonoid Shells

Abstract

Geochemical analyses of ammonoid shells provide an independent and objective data set to evaluate life and habitat of the animal. This uniformitarian consideration, in combination with functional morphology and physical evidence for ecology or physiology, potentially delivers a significant advantage for new insights in paleoecology. One difficulty is that ammonoids as a proxy carrier are assumed to be mobile organisms. In contrast to stationary proxy carriers like benthic bivalves, it is difficult to impossible to estimate absolute depth or locality in which a certain proxy was recorded. Although the temperature proxy is very informative, it could indicate alternative scenarios; shallower calcification depth or calcification in the warmer season. When the calcification temperature is calibrated against the thermal structure of the water column, the proxy records would be fully understood. Therefore, providing the external frame of references is significantly important for getting better insights from geochemical signatures on ammonoids.