Anat Histol Embryol. 2020;00:1–8. wileyonlinelibrary.com/journal/ahe | 1 © 2020 Blackwell Verlag GmbH 1 | INTRODUCTION The capybara (Hydrochoerus hydrochaeris) is the largest rodent in the world (Wilson & Reeder, 2005). Two species are recognized, H. hy- drochaeris and H. isthmus (Patton, Pardiñas, & D’Elía, 2015). They are herbivorous animals of semi-aquatic, gregarious and territorial- ist habits (Cubas, Silva, & Catão-Dias, 2014; Nogueira-Filho, 1996; Pachaly et al., 2001). These animals have a large head in relation to the body, with a rounded snout and cleft upper lips (Antonucci & Ribeiro, 2014; Nogueira-Filho, 1996). They also present phys- ical characteristics associated with their semi-aquatic habits, such as eyes, nostrils and ears located in the same plane, in the upper portion of the head, keeping their senses active during swimming (Antonucci & Ribeiro, 2014; Nogueira-Filho, 1996). The ears are small and rounded, and the eyes are large and developed for night vision (Antonucci & Ribeiro, 2014). Anatomical studies have a crucial role in the biological knowl- edge of wild species and can be used in biological and health areas in different aspects, such as the correct application of surgical or clinical procedures (Brombini et al., 2018; Hirota et al., 2018), and phylogenetic, taxonomic, evolutionary studies (Álvarez, Perez, & Verzi, 2013; Weisbecker & Schmid, 2007). The correct evaluation of radiography and tomography depends closely on the anatomical knowledge of the animal species for the recognition of natural and Received: 27 September 2019 | Revised: 25 November 2019 | Accepted: 20 December 2019 DOI: 10.1111/ahe.12531 ORIGINAL ARTICLE Anatomy of the skull in the capybara (Hydrochoerus hydrochaeris ) using radiography and 3D computed tomography Fernanda Mara Aragão Macedo Pereira 1 | Stela Bonadia de Souza Bete 2 | Letícia Rocha Inamassu 1 | Maria Jaqueline Mamprim 1,2 | Bruno Cesar Schimming 1,3 1 School of Veterinary Medicine and Animal Science, Graduate Program in Wild Animals, São Paulo State University (UNESP), Botucatu, Brazil 2 Department of Animal Reproduction and Veterinary Radiology, School of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, Brazil 3 Department of Anatomy, Institute of Biosciences, São Paulo State University (UNESP), Botucatu, Brazil Correspondence Bruno Cesar Schimming, Department of Anatomy, São Paulo State University (UNESP), Botucatu, SP, Brazil. Email: bruno.schimming@unesp.br Abstract The capybaras (Hydrochoerus hydrochaeris) are the largest rodent found throughout South America and are present in almost all the Brazilian territory, however, still lack basic descriptions about the species, such as about their cranial anatomy. This study was carried out to investigate the anatomical features in the capybara skull. Eight skulls and two heads, without sexual distinction, were used for the osteological, radi- ographic and tomographic identification of their structures. The skull of the capybara could be divided into a neurocranium and a viscerocranium. The capybara had a more robust and rectangular skull, elongated face caudally, thinned in the nasal region and slightly convex in the parietal region. The zygomatic arch was expanded and wide, the orbit had a circular shape, the infraorbital foramen was well developed, exter- nal acoustic meatus and tympanic bulla were relatively small, and the paracondylar process was large. These anatomical characteristics are compatible with the eating habit and semi-aquatic life of capybaras, which can be compared with characteristics reported for animals of similar habits. The radiographic image allowed to identify structures such as the frontal sinus, whereas 3D tomographic reconstruction was essential to have a spatial view of the skull of the capybara. KEYWORDS caviomorph, osteology, radiology, rodent, tomography