Morphometric analysis of some venezuelan akodontine rodents

A systematic review of representatives of the genera Akodon and Microxus fr om Venezuela was performed by univariate and multivariate analyses of skull parameters. Specimens were distributed, according to taxonomic and geograp hic criteria, into the following samples: North (venezuelensis), Northeast (venezuelensis-urichi), South (saturatus), Andes-1 (meridensis), and Andes- 2 (bogotensis). Biometric analyses were complemented with a morphological e xamination of the occlusal surface of the molars. The results indicate that the Andean form bogotensis could be considered as a species of the genus M icroxus, since it is significantly smaller than the other taxa studied. Alt hough there was certain craniometric heterogeneity and variation in the inc idence of particular molar traits between the other morphotypes, the differ ences did not justify a specific distinction. Taking into account their geo graphic distribution, skull size, and morphology of the molar crowns, they could be assigned to Akodon urichi venezuelensis, A. u. meridensis, and A. u. saturatus. The first two are medium-sized subspecies, inhabiting norther n Venezuela and the Andes respectively; the latter is a larger form, which occurs south of the Orinoco river. Two discriminant functions based on skul l and mandible variables respectively were constructed to separate M. bogot ensis from the small-sized forms of Akodon. Differences in the molar morpho logy between A. urichi subspecies appeared in the frequencies of occurrence of the entolophulid of the entoconid of m1 and m2. This variability invali dates the taxonomic value of these dental characters as a diagnostic criter ion for Akodon.