SKELETAL MORPHOLOGY OF THE FORELIMB OFMYRMECOPHAGA TRIDACTYLA

Abstract

Anteater forelimbs are morphologically adapted to obtain food and to provide defense and locomotion. Four species are known, but there are few anatomical studies presenting the morphologic features of each species. The aim of this study was to describe the skeletal morphology of the giant anteater (Myrmecophaga tridactyla) forelimb. Pictures and schematic drawings of six cadavers were created to show the bone morphology. In addition, radiographs and computed tomographs were obtained. The skeletal structure of the forelimb had several notable anatomical features. The scapula had two spines, with apparent differences between infant and adult animals. The humerus had a pectoral ridge, a pectoral tubercle, and a pronounced medial epicondyle that represent the origins of muscles important for fossorial activity. The radius had cranial, lateral, and caudal ridges that became more prominent in older animals, and the distal condyle joint provided enhanced support of the dorsal articulation for the manus. Knowledge of the bone morphology of the forelimb generates a better understanding of giant anteater habits and helps in the diagnosis of skeletal abnormalities and in the routine medical assessment of this species.

Anatomical and radiographic study of the scapula in juveniles and adults of Tamandua mexicana (Xenarthra: Myrmecophagidae)

“…The supraglenoid tubercle in M. tridactyla is located by the authors in the ventral part of the cranial margin of the scapula (Lima et al, ; Sesoko et al, ), but in Tamandua this part is reported as coracoid process (Taylor, ), which is corroborated with our findings in T. mexicana . Although Taylor () does not describe the supraglenoid tubercle in the scapula figures, the origin of the long head of the m. biceps brachii is graphed just cranial to the glenoid cavity, where we found the supraglenoid tubercle in T. mexicana similar to that proposed by Toledo et al () in extinct xenarthrans such as E. fronto .…”

“…The presence of two spines on the lateral surface of the scapula is a characteristic of all xenarthrans (McDonald, Vizcaino, & Bargo, ), which have been named in Tamandua as primary and secondary spines (McDonald et al, ; Taylor, ; Toledo et al, ) or in Myrmecophaga tridactyla as greater and lesser spines (Sesoko et al, ), even in the latter species the lesser spine in another study has been considered as a longitudinal ridge within the infraspinous fossa (Lima et al, ), therefore, to avoid confusion in comparative anatomy with the Nomina Anatomica Veterinaria (ICVGAN, ) and due to its gross anatomical similarity in size (without the acromion) in T. mexicana , we decided to name the second spine as an accessory scapular spine.…”

“…In this surface, there is a line formed by the origin of the m. subscapular, and although this line can be seen in the figures of M. tridactyla , the authors do not describe it (Sesoko et al, ). This surface is less wide in other anteater species as Cyclopes didactylus (McDonald et al, ; Toledo et al, ), and other species of xenarthras as current sloths (Montilla‐Rodríguez, Blanco‐Rodríguez, Nastar‐Ceballos, & Muñoz‐Martínez, ; Toledo et al, ) or extinct species as Eucholoeops fronto (Toledo et al, ).…”

“…The foramen of the n. suprascapular has had various names in different species of xenarthrans, such as: supracoracoid foramen (Taylor, ), coracoides or scapular foramen (McDonald et al, ), supraglenoid foramen (Sesoko et al, ), coracoscapular foramen (Toledo et al, ) and supraspinous foramen (Lima et al, ). In M. tridactyla , it is considered that this foramen is found in adults due to dorsal ossification to the supraglenoid tubercle (Sesoko et al, ), from a separate ossification centre called procoracoids (McDonald et al, ). This has been confirmed in radiographs and macerated scapulae of infants and juveniles of M. tridactyla (Sesoko et al, ) and in our study in juvenile specimens of T. mexicana .…”

“…In M. tridactyla , it is considered that this foramen is found in adults due to dorsal ossification to the supraglenoid tubercle (Sesoko et al, ), from a separate ossification centre called procoracoids (McDonald et al, ). This has been confirmed in radiographs and macerated scapulae of infants and juveniles of M. tridactyla (Sesoko et al, ) and in our study in juvenile specimens of T. mexicana . The scapular incisura in anteater's adults is so superficial that it is named the coracoid groove (Monteiro & Abe, ).…”