The lesser anteater (Tamandua tetradactyla) is not tetradactyla, but pentadactyla

Abstract

The name of the species tetradactyla means “four digits.” In the literature, the hand of the lesser anteater (Tamandua tetradactyla) is described as having four digits (I, II, III and IV) with the absence of a fifth digit. The purpose of this study was to carry out an update adequately proposing an anatomical description of the T. tetradactyla hand. The present findings were analysed on the validation of Morse’s law for this species. In total, seven male cadavers were radiographed and dissected. We observed that the hand of the T. tetradactyla was formed by a carpus containing four bones in the proximal row, which in the medium lateral direction was the radial, intermediate, ulnar and accessory bones of the carpus, and the distal row was formed by carpal bones I, II, III and IV. There were five metacarpal bones (I, II, III, IV and V). The presence of five digits was verified but not confirmed with the literature. Digit I had two phalanges, the proximal and distal; digits II, III and IV had three phalanges: proximal, middle and distal. Digit five had only one phalanx, the proximal, but it was not externally visible. According to the findings of this study, the presence of the fifth digit raises the question of whether the term tetradactyla is the most appropriate to describe this species. This rudimentary fifth digit and the presence of a functional first digit show that the Morse’s law does not applies for the T. tetradactyla species.