The bony labyrinth of Oreopithecus bambolii

We present here a virtually complete Oreopithecus bony labyrinth electronically reconstructed from high-resolution μCT-scanning. Extensive comparative investigation has shown a remarkable diversity in the bony labyrinth of extant and extinct mammal taxa, and has demonstrated its potential for yielding information about phylogenetic relationships and locomotor agility. The latter relationship is based on the semicircular canal system’s contribution to the sensory control of locomotion, including stabilization of the head and eyes, by recording the angular motion of the head. The bodysize related arc-sizes of the semicircular canals (SCs) are known to be a determinant of their sensitivity. The primary aim of this contribution is to provide anatomical information on the still poorly documented ancestral condition of the hominid (i.e., great ape and human) bony labyrinth. The Oreopithecus canal sizes, anterior canal shape, and torsion of the posterior canal are here considered in a comparative primate context, in which extant great apes are characterized by (i) smaller canal arc sizes for their body mass (most strikingly when compared to hylobatids); (ii) a lower anterior canal arc; and (iii) a reversed torsion of the posterior canal. A further aim of this study is to detect morphological and morphometric clues in the bony labyrinth that could help in discriminating between locomotor and positional behaviors that have been suggested for Oreopithecus.