Similarities between jackals and coyotes led Lorenz Oken, in the third volume of his Lehrbuch der Naturgeschichte (1815), to place these species into a new separate genus, Thos, named after the classical Greek word θώς "jackal", but his theory had little immediate impact on taxonomy at the time. Angel Cabrera, in his 1932 monograph on the mammals of Morocco, questioned whether or not the presence of a cingulum on the upper molars of the jackals and its corresponding absence in the rest of Canis could justify a subdivision of that genus. In practice, Cabrera chose the undivided-genus alternative and referred to the jackals as Canis instead of Thos.[1]