NEW OBJECTIVE NON-DESTRUCTIVE METHOD FOR IDENTIFYING MIDDLE JURASSIC NERINEOIDEA GASTROPODS

Accurate identification of fossils is the basis of systematic taxonomy, correct stratigraphic associations and reliable paleoecological implications. Yet, many taxa are identified in a subjective manner that is largely based on expert judgment and difficult to replicate. Nerineoidea gastropods, commonly used for biostratigraphy, formed a major component of Mesozoic carbonate rocks and were widely distributed in shallow marine environments. These gastropods have distinctive internal spiral folds that developed inside the shell, which form the basis of their classification. The aim of the current study was to develop an objective, quantitative, non-destructive method to identify Nerineoidea gastropods.

Fifty eight Middle Jurassic Nerineoidea specimens from Europe, Asia (Arabia) and Africa were examined. Twenty eight specimens were µCT-scanned and optimal longitudinal cross-section images were selected from their tomographic reconstructions. The rest of the specimens were analyzed using images of polished cross sections from published sources (i.e., collections, online databases and literature). Three successive longitudinal whorl sections showing the internal folds were analyzed for each specimen. The shape and location of folds in each whorl section was captured using thirty evenly distributed landmarks and was analyzed using accepted geometric morphometrics methods. Multivariate analysis show that the shape of the folds significantly differentiate between Nerineoidea taxa, independent of data acquisition method or location of the fold in the spire.

We demonstrate that shape analysis of folds is an objective quantitative method for identifying different taxa of Nerineoidea and could revolutionize their classification. The advantages of the method include its application to poorly preserved and taphonomically modified specimens, as well as to two-dimensional images. The quantitative and objective taxonomic identification of Nerineoidea fossils will improve the paleoecologic reconstruction of Mesozoic carbonate platforms. This will enhance interpretations of faunal biogeographic response to changing environmental conditions along shelf ecosystems.