Multivariate analyses of cranial morphology inform the taxonomy and evolution of geomyoid rodents

Morphological analyses are critical to quantify variation within and across species, identify taxa, understand species relationships, and shed light on evolutionary patterns. This work is particularly important in groups that display great morphological disparity. Such is the case in geomyoid rodents, a group that includes two of the most species-rich families of rodents in North America: the Geomyidae (pocket gophers) and the Heteromyidae (kangaroo rats, pocket mice, and their relatives). We assessed variation in skull morphology (including both shape and size) among geomyoids to test the hypothesis that there are statistically significant differences in cranial measurements at the family, genus, and species-levels. Our sample includes a total of 886 specimens representing all geomyoid genera and a total of 39 species. We used the geometric mean of all specimens in the dataset to compare size across taxa. We also used 14 measurements of the skull and lower jaw normalized for size and multivariate statistical methods to compare shape among and within taxa. Our results show that cranial measurements enable the distinction of geomyoids at the family, genus, and species levels. There is a larger amount of size variation within Geomyidae than within Heteromyidae. Our phylomorphospace analysis shows that the skull shape of the common ancestor of all geomyoids was more similar to the common ancestor of heteromyids than that of geomyids. Geomyid skulls display negative allometry whereas heteromyid skulls display positive allometry. Within heteromyids, dipodomyines and non-dipodomyines show significantly different allometric patterns.Paleontological Society Norman Newel AwardCollege of Arts and Sciences Regional Campus Research and Creative Activity GrantResearch Grant from the Ohio State University at MarionSummer Research Assistantship funds from the Ohio State University at MarionNo embargoAcademic Major: Biolog