Morphological adaptations of incisors in the subterranean Gansu zokor, Myospalax cansus (Rodentia, Spalacidae)

The incisor morphology of rodents varies a good deal among different genera and each structure may have a special evolutionary significance. Some basic and lateral profile measurements of upper and lower incisors which may reflect morphological adaptations of the Gansu zokor (Myospalax cansus, a typical subterranean rodent in northern Asia) and the brown rat (Rattus norvegicus, a typical aboveground rodent that has close body size to the Gansu zokor) were analyzed. GIS (Geographic Information System) software and nonlinear regression were used to analyze incisor lateral profile, allowing the incisors to be viewed as circular arcs with a high degree of accuracy. The results show that: i) zokors have more robust (i.e. larger anteroposterior diameter and transverse diameter values), heavier and longer upper as well as lower incisors than rats; ii) zokors show a significantly higher level of sexual dimorphism (male dominant) than rats on the incisor morphology (including basic and lateral profile measurements) and iii) the upper incisor is heavier than lower incisor in rats, as opposed to zokors, in which the lower incisor is heavier than the upper incisor, indicating that more resources must have been allocated to lower incisors of zokors.