Until 1998, all bottlenose dolphins were considered members of the single species "T. truncatus". In that year, the Indo-Pacific bottlenose dolphin was recognized as a separate species. The Indo-Pacific bottlenose dolphin is generally smaller than the common bottlenose dolphin, has a proportionately longer rostrum, and has spots on its belly and lower sides. It also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw compared to 21 to 24 for the common bottlenose dolphin. Some evidence shows the Indo-Pacific bottlenose dolphin may actually be more closely related to certain dolphin species in the genera "Stenella" and "Delphinus", especially the Atlantic spotted dolphin ("S. frontalis"), than it is to the common bottlenose dolphin.