The characteristics of tympanic bullae have adaptation value. Based on the recent studies in the genus Meriones; meatus is the only part of tympanic bullae which has a taxonomic value. In this study, we examined interspecific changes of tympanic bullae in three species of this genus and also the relation of these changes to the climatic conditions of the regions was studied in tow species. Three species: M. persicus, M. libycus, M. crassus were studied by Outline method using eigenshape analysis and elliptical Fourier analysis. Three populations of M. libycus from Birjand, Bardsir (Kerman) and Mashhad; three populations of M. persicus from Geno in Bandar abbas, from Varamin in Tehran and Birjand in Central Khorasan provinces. Our studies support the previous result for taxonomic value of meatus part based on result of elliptical Fourier analysis. They also indicate that hypertrophy on meatus is closely related to climatic and geographical conditions. It is related to the temperature changes and shows a cline with temperature between populations of one species.

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