Fetal bone development in the lowland paca ( Cuniculus paca , Rodentia, Cuniculidae) determined using ultrasonography

This study describes the bone development during the intrauterine phase of the black agouti (Dasyprocta fuliginosa), discussing its relationship with the species’ adaptive strategies and comparing it with other precocial and altricial species. We analyzed 33 conceptuses (four embryos and twenty-nine fetuses) obtained through collaboration with local hunters in the Amazon. Mineralization measurements of the axial and appendicular skeletons were performed by ultrasonography using a 10–18 MHz linear transducer. The chronological order of occurrence of mineralization in relation to the total dorsal length (TDL) and to the percentage of the total gestational period (GP) was: skull, ribs, vertebral bodies, clavicle, scapula, humerus, radius, ulna, ilium, ischium, femur, tibia, and fibula (TDL = 8.2 cm, 48 % GP); metacarpi, metatarsi and pubis (TDL = 9 cm, 51 % GP); thoracic and pelvic limb phalanges (TDL = 13.2 cm, 65 % GP); carpus (TDL = 15.10 cm, 72 % GP) and distal row of tarsus (TDL = 19.6 cm, 87 % GP). Mineralization of the patella was not observed in any advanced fetus (fetus with> 80 % GP). Regarding secondary ossification centers, the first signs of mineralization were observed in the distal epiphysis of the radius, distal epiphysis of the femur, and proximal and distal epiphysis of the tibia (TDL = 13.2 cm, 65 % GP). Fetuses at birth (TDL > 21.5 cm, 93.5 % GP) showed mineralization in all primary centers, and in most secondary ossification centers. Black agouti neonates have a high level of precociality with well-developed skeletal system at birth, which promotes independent postnatal locomotion and dexterity to manipulate and forage in search of food. Our results can contribute to the monitoring of bone development in other wild species, providing parameters for the identification of gestational age and serving as a model for comparisons between precocial and altricial mammals, ultimately helping understand life history strategies in different species.