Meeting Abstract
The nine-banded armadillo (Dasypus novemcinctus) is a member of the family Dasypodidae, which contains all species of armadillos and represents the most diverse group of xenarthran mammals by their speciation, form, and range of digging ability. This study aims to identify muscle traits that reflect specialization for fossorial habit by directly observing forelimb structure in D. novemcinctus and comparing it among armadillos using available myological data as characters for future phylogenetic analysis. A number of informative traits were observed among Dasypodids, including the absence of m. rhomboideus cervicis and profundus, a scapular insertion of m. pectoralis profundus, the variable presence of m. articularis humeri and m. coracobrachialis, a lack of muscle mass for antebrachial supination, and two heads of m. triceps brachii with a scapular origin. Muscle mass and myosin heavy chain (MHC) isoform content were additionally quantified from our forelimb dissections. Notably, nearly 50% of the forelimb muscle mass is devoted to forelimb retraction and 25% to elbow extension, with fast MHC-2X as the predominant isoform expressed across all muscles studied. The digital and carpal flexors contain the greatest amount of the MHC-2A isoform, corresponding with an overall fast-to-slow shift in MHC expression along the length of the forelimb. Collectively, the findings emphasize muscle mass and power output for limb retraction and specialization of the distal limb for sustained purchase of soil by strong pronation and carpal/digital flexion. Moreover, the data assessed here provides a valuable resource for interpretation of myology and internal muscle architecture among digging mammals.
