A landmark-based approach for assessing the reliability of mandibular tooth crowding as a marker of dog domestication

Tooth crowding is one of several criteria used to infer the process of domestication in the zooarchaeo-logical record. It has been primarily used to support claims of early animal domestication, perhaps most contentiously in claims for the existence of so-called proto-domestic dogs as early as the Middle-Upper Palaeolithic. Tooth crowding studies vary in their methodological approaches, and interpretation of the resulting data is constrained by the limited geographic and temporal scope of reference specimens used to construct an appropriate comparative framework. To address these key problems, we present a standardised landmark-based protocol for the measurement and quantification of mandibular tooth crowding that can be systematically applied in the context of dog domestication research. We then test the assumption that tooth crowding is less frequent in ancient and modern wild wolf populations by examining 750 modern dogs and 205 modern wolves from across the modern geographic range of Canis lupus as well as 66 Late Pleistocene wolves from Alaska. Our results demonstrate that landmark-based metrics provide a reliable approach for recording and analysing tooth crowding. Although it is likely that the relatively low frequency of tooth crowding found in our modern dog dataset (similar to 6%) in part reflects the 'modern' morphology of domestic breeds, the higher frequency of crowding in both modern (similar to 18%) and ancient (similar to 36%) wolves strongly suggests that current assumptions linking tooth crowding with the process of early domestication (at least in dogs) should be critically re-evaluated, and that further investigations into the drivers behind these developmental patterns should be pursued. (C) 2017 The Authors. Published by Elsevier Ltd.