At a lower phylogenetic level, the tarsiers have, until recently, all been placed in the genus "Tarsius", while it was debated whether the species should be placed in two (a Sulawesi and a Philippine-western group) or three separate genera (Sulawesi, Philippine and western groups). Species level taxonomy is complex, with morphology often being of limited use compared to vocalizations. Further confusion existed over the validity of certain names. Among others, the widely used "T. dianae" has been shown to be a junior synonym of "T. dentatus", and comparably, "T. spectrum" is now considered a junior synonym of "T. tarsier".