GEOMETRIC MORPHOMETRICS AND THE DEVELOPMENT OF COMPLEX STRUCTURES: ONTOGENETIC CHANGES IN SCAPULAR SHAPE OF DASYPODID ARMADILLOS.

Abstract

Abstract The ontogenetic development of the scapula of Euphractus sexcinctus and Dasypus novemcinctus was studied using geometric morphometrics techniques. The relative importance of uniform, large, and small scale shape changes on ontogenetic development was assessed both by multivariate regression of shape on size and by relative warps analysis. The scapular development in both species is very similar and is characterized (and dominated) by an enlargement of the teres major process. This process serves as origin for the teres major muscle, which is responsible for limb retraction (an important function for digging behavior). There is also a global increase in relative anteroposterior length, increasing the moment arm of this muscle. The uniform shape changes during development are responsible for a small percentage of the size-based shape variation in Euphractus , and for a large percentage in Dasypus . The large scale localized shape changes (which depict the teres major process enlargement) are responsible for a large percentage of size-based shape variation. The region of the coracoid process and glenoid cavity are almost unaltered during the ontogeny in both species.