Evolutionary Inferences Based on Thoracic Limb Muscles of South American Coati ( Nasua nasua ): Brachium and Craniolateral Antebrachium

The South American coati (Nasua nasua) is a mammal of the order Carnivora and family Procyonidae, characterized by scansorial locomotion. Accordingly, several anatomical and functional studies examined its thoracic limbs. Nevertheless, the anatomical descriptions and terminology differ among those studies, and none considered the evolutionary derivations of the brachium and antebrachium muscles based on topology, innervation and anatomical variants. Therefore, the present study aimed to infer the muscle derivations and reconstruct muscle maps of the brachial and craniolateral antebrachial muscles in N. nasua based on the evidence from direct gross dissections and comparisons with literature in embryology and myology of representative mammals from monotremes to procyonids. The caudomedial group will be addressed in a separate manuscript. Seventeen thoracic limbs from eight formaldehyde-fixed specimens and one fresh specimen of N. nasua were dissected. As main results that differed from the available literature, the cranial part of the tensor fasciae antebrachii muscle of non-Nasua procyonids was not lost in N. nasua but fused to the caudal part. The anconeus medialis muscle was not a head of the triceps brachii muscle and may have derived from the caudomedial antebrachial musculature. The caput accessorium of the triceps brachii muscle may have derived mainly from its caput laterale. The extensor carpi radialis muscle was undivided proximally and only separated into two bellies (longus and brevis) from the middle third of the antebrachium. In conclusion, the brachium and craniolateral antebrachium muscles of N. nasua had several differences from those described previously, and most evolutionary derivations could be inferred.