DISTINGUISHING MUS SPICILEGUS FROM MUS MUSCULUS (RODENTIA, MURIDAE) BY USING CRANIAL MEASUREMENTS

The skulls of the two members of the genus Mus, the outdoor, aboriginal Mus spicilegus and the commensal M. musculus can be differentiated using the zygomatic coefficient (CZ). However, the CZ-method does not differentiate all Mus specimens because the cranial measurements needed to calculate CZ are subjective due the unfixed endpoints. Measurement error can contribute significantly to erroneous species classification of specimens if only a single set of measurement is used. The primary aim of our study was to define and rest the measurable characters on a large number of skulls in order to definite separate of the two species. Based on the F-values derived from Discriminant Function Analysis, we found the following three variables contributed considerable to the total discrimination power: width of the zygomatic arch (B), width of first upper molar (MW) and width of the upper ramus of the zygomatic process of maxilla (A). By the classification functions the most discriminating character is MW. For discriminating the above-mentioned two species Fisher's linear discriminant functions were calculated using the two most powerful discriminating variables. This lead us to formulate the following identification function key for M. musculus and M. spicilegus: 2.1 MW-B = 1.46 mm. We infer that with the use of this key the correct identification approaches 100%. The separation of the two species based on the width of M(1) (first upper molar) is useful from a paleontological viewpoint because teeth are generally the best preserved element among vertebrate fossil remains.