Abstract The Pampa biogeographic province covers a mere 2% of the Brazilian territory (176,496 km²). However, it stands out as a complex and diverse ecosystem, although its mammal communities are still scarcely understood. Human activities are transforming the territory into a mosaic of agroecosystems, native and exotic forest fragments, and grasslands. Here we conducted the first investigation to determine the richness of small mammal assemblages in the region based on extensive analyses of owl pellets (Tyto furcata). Craniodental remains were studied from samples collected from 12 Semi-deciduous Seasonal Forest sites in the municipality of São Lourenço do Sul, State of Rio Grande do Sul, Southern Brazil. A total of 2,617 individuals belonging to 18 taxa were recorded, including 2 marsupials (Didelphidae; 0.42%), 2 chiropterans (Molossidae, Phyllostomidae; 0.12%), and 14 rodents (Cricetidae, Muridae, Caviidae; 99.46%). The rodent genera Oligoryzomys, Mus, Calomys, and Akodon were the most common taxa. Large samples also included poorly known taxa, such as the cricetids Bibimys, Juliomys (recording here its southernmost occurrence), Lundomys, and Wilfredomys. From a biogeographical point of view, the recorded assemblage embraces a mixture of Platan, Pampean, and Atlantic Forest elements, highlighting the role of the southernmost Brazilian hills as a wedge favoring the penetration of forest micromammals to higher latitudes. Our findings testify to the great diversity of the Pampa, but also point to a growing homogeneity and dominance of rodent species that are widespread in agroecosystems. Rapid inventories based on owl pellets emerge as a suitable, economic, non-invasive tool to document these community changes.

O gênero Cavia inclui quatro espécies no Brasil, C.aperea (pelo menos duas subespécies, C.a.aperea e C.a.pamparum), C.magna, C.intermedia e C.fulgida. Visando contribuir para o conhecimento da anatomia e para a distinção dessas espécies, descreve-se o sincrânio (crânio e mandíbula) de exemplares de C.a.pamparum do Rio Grande do Sul e compara-se com exemplares de C.magna deste estado e de Santa Catarina, C.intermedia da ilha de Moleques do Sul, na costa catarinense, e C.fulgida de Minas Gerais e Paraná. Cavia aperea possui crânio baixo e longo; rostro comprimido lateralmente; constrição interorbital marcada; órbita elíptica com ampla comunicação com a fossa temporal; forâmen infra-orbital amplo e deprimido; mandíbula longa e baixa, com processo angular não refletido lateralmente; fórmula dentária 1I.0C.1P.3M; dentes hipselodontes; molariformes formados por dois prismas, o anterior laminar e o posterior cordiforme. Cavia aperea distingue-se de C.magna pelo menor desenvolvimento da porção rostral do crânio e da raiz ventral do processo zigomático do maxilar; forâmen infraorbital mais deprimido; porção posterior dos frontais e parietais menos convexos; apófises paraoccipitais mais curtas e curvas anteriormente; incisivos superiores mais estreitos e geralmente opistodontes (proodontes em C.magna); fenda terciária externa (fte) mais profunda e com mais cemento; prolongamento anterior à fte mais desenvolvido e constrição na base do prolongamento posterior. Cavia intermedia possui jugal curto; fossa jugal reduzida/ausente; depressão na região interorbital bem marcada; crista sagital larga; constrição lateral no basisfenóide tênue; forâmen magno amplo; supra-occipital baixo; fte rasa e prolongamento anterior pouco desenvolvido; p4 com prisma posterior tão largo quanto o anterior; m3 com prisma anterior mais largo que o posterior e fenda secundária interna menos profunda. Cavia fulgida caracteriza-se por suas dimensões menores e fte muito profunda. Entretanto, exemplares do sul do Brasil com estes caracteres, mas coloração não típica de C.fulgida, podem pertencer à C.aperea, sendo necessários mais estudos para esclarecer esta questão.

The genus Cavia includes four species for Brazil, C.aperea (at least two subspecies, C.a.aperea and C.a.pamparum), C.magna, C.intermedia and C.fulgida. Aiming to contribute to the anatomy and to distinction of these species the syncranium (skull and mandible) of C.a.pamparum from Rio Grande do Sul State is described and compared with C.magna from Rio Grande do Sul and Santa Catarina States, C.intermedia from Moleques do Sul island on Santa Catarina's coast, and C.fulgida from Minas Gerais and Paraná States. Cavia aperea skull is lower and longer, with laterally compressed rostrum; marked interorbital constriction; elliptical orbit with broad communication with temporal fossa; broad and depressed infraorbital foramen; longer and lower mandible, with angular process not reflected laterally; dental formula 1I.0C.1P.3M; hypselodont teeth; molariforms formed for two prisms, the anterior laminar and the posterior cordiform. Cavia aperea distinguishes from C.magna by a less developed rostrum and ventral root of zygomatic process of maxilla; infraorbital foramen more depressed; posterior portion of dorsal surface of frontals and parietals less convex laterolaterally; paraoccipital apophysis shorter and more bent anteriorly; superior incisors narrower and generally opistodonts (proodonts in C.magna); external tertiary notch (fte) deeper with a thicker cement; anterior prolongation to fte more developed; and a constriction at the bottom of posterior prolongation. Cavia intermedia is distinguished by a shorter jugal; reduced/absent jugal fossa; more prominent depression in the interorbital region; larger sagittal crest; less marked lateral constriction in basisphenoid; wider magnum foramen; lower supraoccipital; fte less marked and its anterior prolongation little developed; the anterior prism of p4 as large as the posterior; anterior prism of m3 larger than posterior; shallow internal secondary notch in m3. Cavia fulgida differentiates by the smaller dimensions and a deeper fte. However southern Brazil specimens with these characters, but not typical coloration of C.fulgida, should belong to C.aperea. More studies are needed to clarify this issue.