Bony labyrinth shape differs distinctively between modern wolves and dogs

Additional reliable anatomical markers are needed for differentiating archaeological wolves and dogs, to support clarifying the origin(s) of dogs. Candidate structures should have good potential to survive various taphonomic conditions. The petrous bone is one potential differentiating structure, and could be further useful when aDNA cannot be extracted otherwise. The petrous bone houses the bony labyrinth (semicircular canals, vestibule, and cochlea). Across a number of taxa, its intricate shape has been shown to carry indicator taxonomic information, supporting clear distinctions between and among mammalian groups. In this report, we explore the three-dimensional shape of the bony labyrinth of wolves and dogs, using micro-computed tomography and 3D geometric morphometrics. We examined 20 modern Eurasian wolves and 20 modern mesaticephalic dogs with comparable skull lengths. We show that dogs have on average a significantly smaller bony labyrinth than wolves. In shape space, wolves and dogs form significantly different, non-overlapping clusters with dogs having a larger relative size of the lateral semicircular canal, smaller relative size of the vertical canals and oval window, and shorter relative cochlea streamline length, with a more antero-ventrally tilted modiolus. These shape differences are not related to allometric effects. Results of this study warrant examination of preserved archaeological and paleo-ontological petrous bones from the oldest possible dogs and isopatric wolves