Data from: Geometric morphometric analyses of worn cheek teeth help identify extant and extinct gophers (Rodentia: Geomyidae)

Studies of the biostratigraphy and palaeoecology of fossil vertebrate assemblages require large samples of accurately identified specimens. Such analyses can be hampered by the inability to assign isolated and worn remains to specific taxa. Entoptychine gophers are a diverse group of burrowing rodents found in Oligo-Miocene deposits of the western United States. In both entoptychines and their extant relatives the geomyines, diagnostic characters of the occlusal surface of the teeth are modified with wear, making difficult the identification of many isolated fossil teeth. We use geometric morphometrics to test the hypothesis that tooth shape informs taxonomic affinities and expected levels of morphological variation across gopher taxa. We also incorporate data from microcomputer tomography to investigate changes in occlusal surface shape through wear within individuals. Our analyses demonstrate the usefulness of our approach in identifying extant geomyines to the genus, subgenus and species levels, and fossil entoptychines to the genus and, in some cases, the species level. Our results cast doubt on the validity of some species within Entoptychus and suggest future revisions to entoptychine taxonomy. The amounts of morphological divergence observed among fossil and extant genera are similar. Fossil species do not differ greatly from extant ones in that regard either. Further work evaluating the morphological variation within and across entoptychine species, including unworn teeth and osteological material, will allow revised analyses of the biostratigraphy and palaeoecology of important Oligo-Miocene mammalian assemblages of the western United States and help to infer the phylogenetic relationships and evolution of gophers.

针对脊椎动物化石组合的生物地层学与古生态学研究，需要获取大量经准确鉴定的标本。此类分析常因无法将孤立且磨损的化石遗骸归属于特定类群而受阻。内囊鼠类（Entoptychine）是一类分布于美国西部渐新世-中新世沉积层中的多样穴居啮齿类。在内囊鼠类及其现生类群囊鼠亚科（geomyines）中，牙齿咬合面的鉴别特征会随磨损发生改变，这使得多数孤立化石牙齿的鉴定难度大幅提升。本研究采用几何形态测量学（geometric morphometrics）验证如下假说：牙齿形态能够反映囊鼠类的分类亲缘关系以及不同类群间预期的形态变异程度。此外，本研究结合显微计算机断层扫描（microcomputer tomography）数据，探究了单个个体牙齿咬合面形态随磨损发生的变化。分析结果表明，该方法可有效将现生囊鼠亚科类群鉴定至属、亚属与物种层级，同时可将化石内囊鼠类鉴定至属级别，部分类群可鉴定至物种级别。本研究结果对内囊鼠属（Entoptychus）内部分物种的分类有效性提出了质疑，并提示未来需对内囊鼠类的分类系统进行修订。化石类群与现生类群间的形态分化程度整体相近，化石物种与现生物种在该维度上亦无显著差异。未来需进一步开展研究，评估内囊鼠类物种内部及物种间的形态变异（包括未磨损牙齿与骨学材料），这将有助于对美国西部重要渐新世-中新世哺乳动物化石组合的生物地层学与古生态学开展修订性分析，并为解析囊鼠类的系统发育关系与演化历程提供支撑。