MORPHOMETRIC VARIABILITY WITHIN ASTARTE FROM THE PLIOCENE OF THE ATLANTIC COASTAL PLAIN

The bivalve genus Astarte is a cosmopolitan genus that is commonly found within the Atlantic Coastal Plain of the United States. This genus has many formally named species, even though it lacks many features that would encourage diversification. As a result, the validity of some Astarte taxa have been called into question. A well-defined taxonomy is a key component to the reliable testing of paleoecological hypotheses. A morphometric analysis of 830 specimens representing nine species from the Pliocene was conducted. A total of 9 geometric landmarks and 5 pseudo-landmarks were collected from scaled digital photographs using ImageJ. Procrustes transformation and Principle Components Analysis (PCA) was performed on the collected dataset using R.

The PCA results show a large amount of overlap between all species. PC1 and PC2 account for 50.59% of the overall variance. Astarte concentrica and Astarte undulata show the most phenotypic variation. These two species occupy their own morphospace with minimal overlap. The other seven species show considerable overlap with the morphospaces of A. concentrica and A. undulata. Most of these seven species fall within the morphospace of Astarte floridana which demonstrates an intermediate morphology between A. concentrica and A. undulata.

The overlap in the morphospaces show there are many phenotypic similarities between these species. Each morphospace also shows there is much variability to be found within a single species of Astarte. A. concentrica and A. undulata possessing their own morphospace suggest these two species are likely separate, and valid, but have high amounts of intraspecific variation. The remaining species plotting within the morphospace of A. floridana suggest these species have similar morphologies. These species merit a further look as several of them could likely be synonymized. The PCA results did not capture variation of the posterior margin that is present in species from Florida. An outline analysis paired with the current results will better explain this variation.

The potential to synonymize several species within this genus could provide an easier to manage and more reliable taxonomy within the Atlantic Coastal Plain. This cleaner taxonomic group will allow for more rigorous and easily replicable studies to be conducted using these species.