Taxonomic identification using virtual palaeontology and geometric morphometrics: a case study of Jurassic nerineoidean gastropods

Taxonomic identification of fossils is fundamental to a wide range of
geological and biological disciplines. Many fossil groups are identified
based on expert judgment, which requires extensive experience and is not
always available for the specific taxonomic group at hand. Nerineoideans,
a group of extinct gastropods that formed a major component of Mesozoic
shallow marine environments, have distinctive internal spiral folds that
form the basis for their classification at the genus level. However, their
identification is often inconsistent because it is based on a set of
selected characters reliant upon individual interpretation. This study
shows a non-destructive and quantitative method for their identification
using micro-CT and geometric morphometrics. We examined and
micro-CT-scanned nerineoidean specimens from five main families that
dominated Europe, Arabia and Africa during the Middle-Late Jurassic.
Optimal longitudinal slices were selected from the tomographic
reconstructions or from images of polished cross-sections compiled from
fossil collections, published work and online databases. Internal whorl
outlines were represented by thirty evenly distributed sliding
semilandmarks and shape variations were studied using the Procrustes-based
geometric morphometrics method. Multivariate analysis shows that
Ceritellidae and Ptygmatididae are distinct families, whereas
Nerinellidae, Eunerineidae and Nerineidae fall within the same shape
variance and cannot be distinguished based on internal whorl outlines. The
suggested method can be applied to images from various sources as well as
to poorly preserved specimens. Our case study demonstrates the importance
of quantitatively re-evaluating taxonomy in the fossil record, promoting
the future utility of large datasets.