A morphometric comparison of the cranial shapes of Asian dwarf hamsters (Phodopus, Cricetinae, Rodentia)

Abstract

Phodopus is the smallest cricetine genus, consisting of the dwarf hamsters (Phodopus sungorus, Phodopus campbelli, and Phodopus roborovskii) of arid central and east Asia. Persistent taxonomic issues in this genus include (1) whether P. sungorus and P. campbelli are con- or heterospecific and (2) whether P. roborovskii is con- or heterogeneric with the aforementioned species. To shed new light on these questions, the crania of Phodopus species were compared to each other using geometric morphometrics. Furthermore, to determine what cranial traits are shared by Phodopus crania, they were compared to the more ‘typical’ small hamster Nothocricetulus migratorius. The three Phodopus species significantly differed in cranial size and shape from each other and from N. migratorius. A large part of shape variation was allometric with only weak evidence for unique allometries. All four species lacked sexual dimorphism in cranial size and shape. As a genus, Phodopus is characterized by small-sized crania, that are broad, short, and with flaring zygomatic arches. They also have reduced rostra and enlarged foramina magna. P. roborovskii was the most distinct Phodopus, characterized by its smaller-sized cranium, with greater breadth, a rounder braincase and orbit, a shorter incisive foramen and rostrum, a larger foramen magnum, and smaller bulla with a longer eustachian tube. The crania of P. sungorus and P. campbelli are very similar, but they do diverge in relatively minor (statistically nonsignificant) features, such as cranial roundness, as well as the size of the molar row, bulla, zygomatic arch, and incisive foramen. Shape differences conformed to phylogenetic distance and with habitat differences.