<b>Studies on the pelvis in British Muridae and Cricetidae (Rodentia)</b>

Abstract

The morphology and its variation of the bony pelvis in British species of Muridae and Cricetidae have been studied. The investigation began with the application of a mensural method for demonstrating sexual dimorphism and it is shown that for all species except those of Rattus the male os coxa can be distinguished from the female over a wide range of ages. During the study it became obvious that there are ranges of morphological variation in os coxae both inter‐ and intraspecific. There are constant interpecific differences which allow identification of os coxae of these rodents at least to genus and in many cases to species. Detailed descriptions of the morphology of the os coxa of each species are given together with an identification key. Intraspecific variation is mainly sex‐dependent and comprises sexual dimorphism, male pubertal changes and female parturition changes. The changes in the male are from epicene, through pubertal, to post‐pubertal phase, with the first of these resembling the agonadal, female, form and the last with a posterior border thickened and tuberculate in relation to the hypertrophied penis and its associated glands and musculature. These phases are not equally obvious in all species, but the pelvis in all except Rattus and Mus shows some evidence of the sexual development of the animal. In females the form of the pelvis may be modified during successive pregnancies to allow a wider pelvic outlet for parturition. Resorption and remoulding of the female pelvis allows the recognition of non‐parous, uniparous and multiparous animals in all Cricetid species, in Micromys and, more doubtfully, in Mus , but not in Apodemus and Rattus . Non‐sex‐dependent intraspecific variation, comprising differences in rugosity related to muscularity is also described. The observations are discussed in relation to earlier experimental work, to the need for basic research on small mammal reproduction and population structure, and to the use of the pelvis in the analysis of osteological assemblages, such as occur in owl pellets.