Investigation of climatic effects on the shape and volume of tympanic bulla of Meriones libycus and M. Persicus (Muridae: Rodentia) from Northeastern Iran: An evolutionary approach

The jirds, Meriones persicus and M. libycus are two widespread species in Iran. Meriones libycus can be found in low lands of deserts and semi desert areas, but Meriones persicus in high rocky regions of Khorasan. In this research 190 skulls belonging to Meriones persicus and Meriones libycus of northeast of Iran were at first identified on the basis of morphologic characters, and then were divided regarding wearing quantity of molar teeth surfaces into four age classes in which 20 quantitative cranial and dentary characters were measured. The results show that five characters including Infraorbital thickness, mastoid length, zygomatic width, first mandibular molar length (M/1), and lower cheek teeth length from alveole in different age classes are not significantly different, and can be applied in identification of specimens relating to each of the two species in all age classes. This study also shows that the ratio of bullar length to the skull length in these two species is basically different and in M. libycus is closely related to environmental conditions like humidity and population density. This character can be used as intraspecific population density coefficient about desert and semi desert species and it is important for basic studies relating to adaptation, field studies, and harmful rodents controls.