Cranial variation in bottlenose dolphins Tursiops spp. from the Indian and western Pacific Oceans:: additional evidence for two species

We examined the skulls of 72 bottlenose dolphins from the Indian and western Pacific Oceans to clarify the systematics in genus Tursiops. We also examined type skulls of Tursiops aduncus (Ehrenberg, 1832), T. eurynome (Gray, 1846), T. catalania (Gray, 1862), Delphinus (Steno) gadamu Owen 1866, T. dawsoni Lydekker 1908, and T. truncatus (Montagu, 1821). The specimens were divided into two groups, A and B, based on rostrum length and characters of the basal part of the rostrum. The rostrum of group A was longer and tapered abruptly near the base, whereas that of group B was shorter and tapered more gradually throughout its length. Group A contained specimens from western, central, and eastern Asia, Africa, and Australasia. Group B contained specimens from central and eastern Asia and Australasia. The six type skulls were also clearly divided into two groups; the type skulls of T. aduncus, T. catalania, and Delphinus (Steno) gadamu were included in group A, whereas the type skulls of T. truncatus, T. eurynome, and T. dawsoni were included in group B. This grouping was consistent with the genetic status. Therefore, we identified group A specimens as T. aduncus and group B specimens T. truncatus, the oldest scientific names related to the two groups.