Outline analysis as a new method for investigating development in fossil crabs

Abstract

Geometric morphometrics offer various methods that are often used in the analysis of fossil specimens, due to the specimen's morphological nature. One of these methods, outline analysis, can be applied to compare the shape of specimens in various contexts. Here, we use outline analysis to investigate the developmental stages of fossil specimens. We use the extant European shore crab to test a pipeline where elliptic Fourier analysis and discriminant function analysis are used to provide an objective interpretation of a specimens' developmental stage. We then test the pipeline, using a case of a recently redescribed juvenile fossil crab (Liocarcinus oligocenicus). We find, that in data sets without phylogenetic variation, this pipeline works well in identifying developmental stages. However, it is less efficient when data sets increase in noise. Furthermore, Carcinus maenas expresses a clear morphological separation between juveniles and adults.