In order to study evolutionary pattern and process we need to be able to accurately identify species and the evolutionary lineages from which they are derived. Determining the concordance between genetic and morphological variation of living populations, and then directly comparing extant and fossil morphological data, provides a robust approach for improving our identification of lineages through time. We investigate genetic and shell morphological variation in extant species of Penion marine snails from New Zealand, and extend this analysis into deep time using fossils. We find that genetic and morphological variation identify similar patterns and support most currently recognised, extant species. However, some taxonomic over-splitting is detected due to shell size being a poor trait for species delimitation, and we identify incorrect assignment of some fossil specimens. We infer that a single evolutionary lineage (Penion sulcatus) has existed for 22 million years, with most aspects of shell shape and shell size evolving under a random walk. However, by removing samples previously classified as the extinct species P. marwicki, we instead detect morphological stasis for one axis of shell shape variation. This result demonstrates how lineage identification can change our perception of evolutionary pattern and process.

Additional tables, figures and files for the genetic and morphometric analyses in 'Lineage identification affects estimates of evolutionary mode in marine snails'. This includes the Supplementary Material, as well as genepop and Structure genotype files, and an overall MorphoJ input file containing Procrustes coordinates and centroid size for all sampled shells (with an explanatory spreadsheet). Additional excel spreadsheets provide sample details for specimens used in the genetic and morphometric analyses, and the 'samples-on-NCBI' file provides NCBI accession numbers for all archived genetic data.

The explanatory spreadsheet 'whelkmorpho-guide' provides a guide to the character string used to analyse the 'fulldataset-forMorphoJ' Procrustes coordinate .csv file in MorphoJ.