Data from: Testing the success of palaeontological methods in the delimitation of clam shrimp (Crustacea, Branchiopoda) on extant species

Fossil spinicaudatan taxonomy heavily relies on carapace features (size,
shape, ornamentation), and palaeontologists have greatly refined methods
to study and describe carapace variability. Whether carapace features
alone are sufficient for distinguishing between species of a single genus
has remained untested. In our study, we tested common palaeontological
methods on 481 individuals of the extant Australian genus Ozestheria that
have been previously assigned to ten species based on genetic analysis.
All species are morphologically distinct based on geometric morphometrics
(p ≤ 0.001), but they occupy overlapping regions in Ozestheria
morphospace. Linear discriminant analysis of Fourier shape coefficients
reaches a mean model performance of 93.8% correctly classified individuals
over all possible 45 pairwise species comparisons. This can be further
increased by combining the size and shape datasets. Nine of the ten
examined species are clearly sexually dimorphic but male and female
morphologies strongly overlap within species with little influence on
model performance. Ornamentation is commonly species-diagnostic; seven
ornamentation types are distinguished of which six are species-specific
while one is shared by four species. A transformation of main ornamental
features (e.g. from punctate to smooth) can occur among closely related
species suggesting short evolutionary timescales. Our overall results
support the taxonomic value of carapace features, which should also
receive greater attention in the taxonomy of extant species. The extensive
variation in carapace shape and ornamentation is noteworthy and several
species would probably have been assigned to different genera or families
if these had been fossils, bearing implications for the systematics of
fossil Spinicaudata.