Cranial Differences between Freshwater Amazon River Dolphin (Inia geoffrensis) and Saltwater Bottlenose Dolphin (Tursiops truncatus)

Abstract

Dolphins are widespread aquatic mammals adapted to both freshwater and saltwater environments. There are wide variations in size and shape among them, even in same species from different geographical regions. However, the variation among dolphin populations and its link to the selective pressure in different environments has not been systemically studied. In this study, the skulls from freshwater and saltwater dolphins were compared to assess the relationship between the skull morphology and environment. Twenty seven cranial measurements from the dorsal and ventral aspects of the skull were obtained from 36 Amazon River dolphins (Inia geoffrensis) and 44 marine bottlenose dolphins (Tursiops truncatus) to assess the difference between these two taxa. Data was analyzed using MANOVA. Results demonstrated that there was significant differences between marine and river skulls [Wilk's Λ = 0.006, F (27, 55) = 352.5, p<0.05, partial η2 = 0.99]. Although there were not statistical differences in total length of the skull between freshwater dolphins (457,9±62.0 cm) and saltwater dolphins (466.2±14.9 cm), saltwater dolphins reported significatively narrower skulls than the freshwater dolphins. Further study is needed to elucidate the dietary behavior and masticatory properties of these two taxa in their respective habitats to further explain the adaptation of dolphins to river and marine environments. Support or Funding Information Fulbright Foundation Characters measured from dolphin skulls This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.