INTEGRATING MORPHOLOGICAL AND GENETIC DATASETS TO UNDERSTAND SPECIES DELIMITATION: A CASE STUDY ON TEREBRATULIDE BRACHIOPODS

Considering the crucial role of morphology in species recognition in the fossil record, analyzing morphology in a quantitative manner and comparing phenotypic variability in both fossils and living close relatives is fundamentally important. Living specimens provide additional sources of data (e.g. genetics, ecology, biogeography) to characterize species more accurately. The objective of our research is to understand how terebratulide brachiopod species are delimited by quantifying morphological variability in both extant and fossil specimens. We analyzed long loops—the calcareous structure supporting the lophophore—in extant species by CT scanning the specimens and using 3D geometric morphometrics and statistical methods. Our results demonstrate that named species can be discriminated based on long loop morphology, validating current taxonomic assignments. Even when external shell characters are not considered, the loop offers sufficient resolution to discriminate among named species.

Since long loops are rarely preserved in the fossil record, we integrated our 3D dataset with 2D images of the outlines of their respective dorsal valves to determine if a correspondence between loop and overall shell shape exists. We digitized valve outlines and analyzed them using Elliptical Fourier Analysis (EFA) to quantify variation of shell shape. To quantify morphological correspondence between long loops and outlines we performed a partial least squares analysis (PLS) on Procrustes-fitted coordinates. Although shell outlines offer less resolution, outline data are valuable in discriminating among named species when loops are not present. Finally, to add another source of information that will help test our morphological predictions on species boundaries, we will analyze genetic data of living brachiopods. Species of Terebratalia and Laqueus will be examined using a RADSeq protocol. The resulting DNA sequences will be analyzed under the multispecies coalescent model to estimate species delimitation and population genetic parameters, such as heterozygosity and population differentiation [F_ST]. Comparing genetic and morphologic species delimitation results from extant species will help us determine how species can be successfully discriminated and compared in the fossil record.