Cranial variation across spiny pocket mice (Heteromys, Liomys) in new phylogenetic and taxonomic perspectives

Spiny pocket mice are usually divided into two genera, Heteromys and Liomys, and more recently the latter have been subsumed into the former, leaving subfamily Heteromyinae with one genus. However, this arrangement conveys false equivalency among heteromyines, and does not represent the great morphological, molecular, and ecological diversity in this subfamily. To address this, geometric morphometric methods were used to explore interspecific cranial variation in this subfamily, which were then evaluated in the context of recent phylogenetic and taxonomic findings. The dataset consisted of 65 landmarks on the crania of 328 adult voucher specimens (15 species, 114 localities). Allometry and habitat adaptation are potential explanations for some of the variation patterns. Morphometric clustering among some distant relatives suggests convergent adaptation to similar habitats. These results support recent taxonomic proposals for the subfamily based on molecular phylogenies, in which the three to four main lineages are assigned generic status. We summarize the evidence and describe their scaled cranial shape variation. These lineages consist of Heteromys as traditionally defined (i.e., not including Liomys) while the traditionally defined Liomys would be divided into the genera Schaeferia (S. adspersus + S. salvini), Liomys sensu stricto (L. irroratus), and potentially a fourth (new) undescribed/undiagnosed genus for L. pictus + L. spectabilis. The implications of the present study are that scaled cranial shape variation patterns align better with this modified taxonomy than earlier ones. Our results confirm the usefulness of geometric morphometrics in providing taxonomic insights in taxa that appear cryptic using traditional distance-based measurements.