Anatomia comparada e morfometria de oligoryzomys nigripes e o. flavescens (rodentia, sigmodontinae) no Rio Grande do Sul, Brasil

oligoryzoms flavescens and o. nigripes are widely distributed and sympatryc in many biomes. the diagnostic characters used to recognize these are not clearly established. in this study description and comparison was conducted of external morphology, anatomy of the skull, teeth, postcranial skeleton, as well as stomach and penis morphology. statistical analysis was generated from morphometric data. the sample consisted of 208 specimens from 24 localities in brazil. o. nigripes was found to be larger, with dorsal pelage darker and ventral pelage whitish with black specks, the skull being larger and more robust than o. flavescens. o. flavescens is smaller, with slightly clearer dorsal pelage and yellowish belly. the pattern of cephalic circulation is derived from the second type in both species. comparison of postcranial skeleton reveals prominent accidents in scapula and humerus in o. flavescens. on the other hand o. nigripes demonstrated numerous differences localized in the iliac blade, orientation of the ischium and prominent accidents in tibia and fibula. the stomach morphology of both taxa had the same unilocular-hemiglandular pattern. the penis consisted of distal baculum tri-digited. analysis of the discriminant function clearly indicates the distinction of two homogeneous groups represented by the species. according to t test, two morphometric variables (width of the zigomatic plate and width of first upper molar)are irrelevant (p > 0.05) to the discrimination of taxa. sexual dimorphism based on morphometry was supported by t test for o. nigripes. in o. flavescens this condition was not supported.