In this study, we report a case of duplication of a lower fourth premolar (P4) on an Iberian wild goat from the archaeological site cave of Arlanpe, (Lemoa, Bizkaia, Northern Spain). The preserved right mandible corpus displays two premolars and the first molar (M1). Both premolars conform in size and general shape to fourth premolars (P4) but the medialmost of the two is rotated 90° counterclockwise, and thus, its wear pattern is different. The comparative analysis to other bovids and the relative scarcity of this anomaly compared to other cases of polydontia and hypodontia suggest that it is a developmental defect consisting in the duplication of the tooth germ, and we doubt on the potential of this abnormality as a territorially based indicator of past wild populations as has been previously proposed. Copyright © 2011 John Wiley & Sons, Ltd.