Abstract
Background : In horses, the morphological changes induced by the process of domestication are reportedly lesspronounced than in other species, such as dogs or pigs–although the horses’disparity has rarely been empiricallytested. We investigated shape differences and modularity of domesticated horses, Przewalski’s horses, donkeys andzebras. Mandibular and tooth shape have been shown to be valuable features for differentiating wild anddomesticated forms in some mammals. Results : Both mandible and teeth, show a pattern of shape space occupation analogous to that of the cranium, withdomesticated horses occupying a similar extension in shape space to that of wild equids. Only cranial shape dataexhibit a tendency to separate domesticated horses and Przewalski’s horses from donkeys and zebras. Maximumlikelihood model-based tests confirm the horse cranium is composed of six developmental modules, as reported forplacental mammals in general. The magnitude of integration in domesticated horse skull was lower than in wildequids across all six cranial modules, and lower values of integration were associated with higher disparity valuesacross all modules. Conclusion : This is the first study that combines different skeletal features for the description and comparison of shapechanges in all living equid groups using geometric morphometrics. We support Darwin’s hypothesis that the shapevariation in the skull of domesticated horses is similar to the shape variation of all wild equid species existing today.Lower magnitudes of module integration are recovered in domesticated horses compared to their wild relatives.