Gross Osteology and digital radiography of the common Capybara (Hydrochoerus hydrochaeris), Carl Linnaeus, 1766 for scientific and clinical application

Being able to study anatomical structures of wildlife species for science and clinical practice is of great importance. We aimed to describe the normal gross osteology of the common adult capybara Hydrochoerus hydrochaeris (Linnaeus, 1766), using macerated bone specimens and high-resolution digital radiography. The complete axial and appendicular skeleton was further compared with previously reported anatomical findings. For this purpose, we used three adult capybara cadavers (two females and one male), with a mean bodyweight of ±50 kg. Some H. hydrochaeris-specific morphological characteristics, especially in the skull region, show evidence of adaptation to aquatic life, such as an elongated head shape, with eyes, ears, and nose, located dorsally, to stay above water. Additionally, the entire bone structure demonstrates the size and weight support of the largest rodent and its adaptation with respect to foraging and locomotion behaviors. As a semi-aquatic herbivore, classified as cursorial (having limbs adapted for running), the authors believe it should be reclassified as cursorial-swimming/diving. Moreover, we argue to consider a differentiation between H. hydrochaeris silvestris to H. hydrochaeris synanthrope, due to substantial weight variation, in some cases > 100%. This inevitably has an impact on the development of bone structure, thus influencing habitual adaptation, and consequently, its clinical implications and animal handling. Radiography exams helped in the identification of bone structures, which otherwise were not observed in anatomical specimens, such as ossa sesamoidea, including the ossicle lunulae. Likewise, the radiographs were particularly helpful in overall better comprehension of the intubation and catheterization procedures. We believe this work can contribute as a reference to anatomical studies for students and professionals acting in clinic, surgery, and research.