Atlantic, dolphin, dolphins, genetics, geographic variation, humpback dolphins, Indian Ocean, morphometrics, skull, skull morphology, skulls, sousa, taxonomy
The taxonomy and systematic relationships of humpback dolphins (genus Sousa) are highly confused. This is largely due to a lack of data and samples from large portions of the range of the genus, and confusing and seemingly contradictory patterns of variation in available external morphometric, skeletal morphometric, and molecular datasets. To help clarify the situation, we measured 222 skulls of humpback dolphins originating from throughout most regions of the range of Sousa. While patterns of cranial variation appeared to be relatively conservative, there was evidence for three groups: (1) Atlantic Ocean/West Africa, (2) Western Indian Ocean, and (3) Eastern Indian Ocean/Pacific Ocean. These would appear to correspond to the teuszii, plumbea, and chinensis forms, respectively. No taxonomic revisions are recommended at this time, and the conservative view of two species (S. teuszii in West Africa and S. chinensis in the Indo-Pacific) can be defended for the time-being as a pragmatic approach. The distinctness of S. teuszii is clearcut, but other taxonomic decisions should await further studies of molecular genetics and morphometrics, currently underway.