The occurrence of abnormal upper third molars and lower fourth molars in the Caninae is reviewed. It is proposed that the extra molars normally found in the adult dentition of Otocyon megalotis (Desmarest) are the result of a mutation that caused the duplication of the upper first molar and the lower second molar. Supporting evidence for this is presented. This makes the upper third molar of Otocyon the homologue of the normal canid second molar, and the lower fourth molar the homologue of the normal third molar of all of the remaining canids.