Data, code, and supplementary information for Hyracoid locus identification

Serially homologous elements pose an identification problem in fragmentary records, particularly those of vertebrate fossils. Examples include individual vertebrae in the vertebral column and teeth in a tooth row. Until an isolated element can be accurately attributed to a specific position within its series, multiple lines of ecological and evolutionary research cannot be conducted. However, varying levels of differentiability between loci, and varying patterns of differentiation across clades, make it impossible to develop a single set of diagnostic traits for any particular set of serial homologs, particularly mammalian molars. Here, we test the utility of a set of classification criteria for distinguishing molar tooth positions of hyraxes (Mammalia, Afrotheria, Hyracoidea), which have been considered indistinguishable in previous taxonomic studies. As part of the test, we evaluate the degree to which between-locus variation is conservative in this taxon, which would strengthen the predictive power of proposed traits even in cases where species identity is unknown. Suitable tests for hypotheses of conservatism in categorical traits did not exist, to our knowledge, and we, therefore, explored the behavior of previously developed metrics, Borges et al.’s δ, to assess conservatism in contrast to the phylogenetic signal produced by Brownian motion. This metric shows some promise but the nature of resulting distributions makes tests difficult to interpret, indicating a line of potential future methods improvement. We used a linear morphometric characterization of shape to validate the candidate traits. In the case of hyracoid molars, relatively simple ratios of linear measurements have strong discriminatory power despite evolutionary variation in between-locus differences. Overall, new or understudied taxa are likely to have lower molar loci differentiable by their relative length and talonid vs. trigonid width.

Methods
This dataset contains raw data, a snapshot of code as analyzed, and associated supplementary data describing specimens, scans, and species used in a study attempting to diagnose tooth positions in isolated teeth of Hyracoidea. A live version of the code can be found in the GitHub repository 'hyracoid-locus-example' managed by the lead author (GitHub username: nsvitek). Full citations for associated references can be found in the manuscript associated with this dataset. Raw data consists of linear measures from multiple sources, including direct measurements collected from 3D surfaces in MeshLab and a compilation of published measurements from the literature. Separate datasets from separate sources are kept in separate spreadsheet files. Names correspond to their usage in code. All code was written for the R statistical computing language.