Potentials of closed contour analysis in species differentiation and holotype designation: a case study on lower Norian (Upper Triassic) conodonts

Geometric morphometric approaches become increasingly applied in the fields of biology and paleontology. Taxonomy is a good example, where a long-standing intention of scientists is to eliminate subjectivity as much as possible. In the case of biostratigraphically important conodont elements, the application of such methods is not widespread. Indeed, only a handful of studies attempted to deal with the morphological variance of conodont elements from this aspect. The detailed description of five lower Norian (Upper Triassic) taxa (Ancyrogondolella quadrata, A. rigoi, A. triangularis, A. uniformis and Metapolygnathus mazzai) is presented here based on landmarks and Fourier analysis of the P1 element and keel outlines. Both methods led to similar outcomes regarding taxonomic differentiation and exposing shape variability. Consensus shapes were generated to objectively reveal the typical contour shape of each taxon, which allowed their comparison with each other, and with the members of th...,
Material
The analysis involved a total of 136 lower Norian conodont P1 elements. The material originates from various localities of the western Tethys and western North America. Eighty percent of the specimens were unambiguously assigned to the taxa Ancyrogondolella quadrata, A. rigoi, A. triangularis, A. uniformis and Metapolygnathus mazzai. For specimens bearing morphological characters not fully fitting in the original diagnoses of these species, the open nomenclatural term “ex gr.” (of the group) was used. Holotypes of the listed species were also included in the study based on the best illustrations from the literature. Only non-deformed, complete, adult (GS4-GS6; based on the ontogenetic series defined in Mazza & Martínez-Pérez 2015) specimens were involved in the present study.
Shape descriptors
For the shape description, we chose to analyse the element and the keel outlines. To avoid bias induced by bilaterality, all dextral elements were mirrored into their sinistral coun..., To run the provided scripts, the open-access R programming environment (v4.1.2) and the RStudio desktop application (build 353) is recommended. To begin, \"Virag_Karadi_2023_CONODONTS_script.R\" should be opened with RStudio, and if run step by step, it will load the necessary packages (Morpho), custom functions (\"Virag_Karadi_2023_CONODONTS_functions.R\") and data files (all provided .csv files), automatically during the session.