The study of the cranial endocast provides valuable information to understand the behavior of an organism since it coordinates sensory information and motor functions. In this work, we describe for the first time the anatomy of the encephalon of an early Miocene pan-octodontoid caviomorph rodent (Prospaniomys priscus) found in the Argentinean Patagonia, based on virtual 3D endocast. This fossil rodent has an endocast morphology here considered ancestral for Pan-Octodontoidea and also other South American caviomorph lineages, such as an encephalon with anteroposteriorly aligned elements, mesencephalon dorsally exposed, well-developed vermis of the cerebellum, rhombic cerebral hemispheres with well-developed temporal lobes. Prospaniomys also has relatively small olfactory bulbs, large paraflocculi of the cerebellum, low endocranial volume, and a degree of neocorticalization. Its EQ is lower compared with Paleogene North American and European non-caviomorph rodents, but slightly higher than several late early and late Miocene caviomorphs. The paleoneurological anatomical information supports the hypothesis that Prospaniomys was a generalist caviomorph rodent with terrestrial habits, and enhanced low-frequency auditory specializations. The scarce paleoneurological information indicates that several endocast characters in caviomorph rodents could change with ecological pressures. This work sheds light on the anatomy and evolution of several paleoneurological aspects of this particular group of South American rodents. 

The specimen MACN-PV CH1913 of Prospaniomys priscus was collected in early Miocene levels (Arquitanian–Burdigalian; ca. 20–21 Ma) of the Sarmiento Formation exposed at Pampa de Gan Gan, Chubut Province, Argentina (Fleagle and Bown, 1983; Arnal and Kramarz, 2011). The cranium is externally clean, but inside and in the orbital region it is filled with a hard matrix. The specimen was studied using high-resolution microtomography. The encephalon region was manually segmented and the 3D reconstructions were made using Slicer.

The .stl files can be opened with any program used to explore CT scans or generate 3D models.