Descriptive study of the intrinsic muscles of the shoulder and brachium in kinkajou (Potos flavus) and an evolutionary analysis within the suborder Caniformia

Abstract The kinkajou ( Potos flavus ) is a carnivoran of the suborder Caniformia and the family Procyonidae , inhabiting regions throughout Central and South America. Potos flavus has arboreal preferences and exhibits unique anatomical adaptations that facilitate movement within trees. Its pelvic limbs enable hindfoot reversal, while its thoracic limbs possess remarkable prehensile capabilities. Previous anatomical studies in Potos flavus have presented discrepancies in the description of the intrinsic shoulder and brachial muscles. Therefore, this study aims to provide a comprehensive anatomical description of these muscles in five specimens. The findings are compared with descriptions reported for other caniforms. The application of the Density-Based Spatial Clustering of Application with Noise (DBSCAN) algorithm aids in identifying relationships among caniforms based on the presence or absence of specific muscles. Our analysis reveals several key differences, including the presence of a biceps brachii with two capita (longum and breve), two coracobrachiales muscles (longus and brevis), a tensor fasciae antebrachii with two distinct parts (cranialis and caudalis), and an anconeus medialis. The caput breve of the biceps brachii and coracobrachialis longus muscles are absent in some individuals, with prevalence rates of 10% and 20%, respectively. One specimen exhibited an accessory caput laterale of the m. triceps brachii bilaterally. The comparative analysis suggests that the shoulder and brachial muscles of Potos flavus share more similarities with those of Ailurus fulgens and ursids of the genera Ursus and Tremarctos . These findings suggest the retention of muscles that may have been present in the common ancestor of the infraorder Arctoidea.