Osteological variation and taxonomic affinities of bottlenose dolphins, Tursiops spp., from South Australia

Abstract

Skulls and skeletons of 84 cranially mature bottlenose dolphins collected from South Australia were studied to distinguish morphological groups. The dataset comprised 38 skull measurements, 5 tooth counts/measurements, 6 coded skull features and 2 vertebral counts. There was no significant difference between sexes. Agglomerative, heirarchical cluster analyses performed on all variables and a dataset refined by eliminating those with high partial correlations produced two clear groups of skulls but with some differences in group membership between the statistical treatments. Size was an important factor in distinguishing groups, especially when categorical variables were excluded. Groups produced by cluster analysis of all variables were aligned with Tursiops truncatus and T. aduncus. In general, Tursiops truncatus was distinguished by a wide band (3-9 mm) of cancellous bone on the premaxillae, a distinct supraoccipital crest, raised naso-frontal complex, the almost complete lack of bone resorption on the pterygoid bones, a relatively wider rostrum, generally larger skull size (condylobasal length >465 mm versus <476 mm, except two skulls of 445 and 448 mm), and more than 60 vertebrae. This species was collected from open ocean coasts and sometimes stranded in groups. Tursiops aduncus generally had a narrow or no band of cancellous bone (0-5 mm), an indistinct or no supraoccipital crest, a naso-frontal complex that was not markedly raised, moderate to extensive bone resorption on the pterygoids, relatively narrow rostrum, fewer than 63 vertebrae and was collected mainly from the large gulfs. There was no significant difference between tooth diameter of T. aduncus and T. truncatus from South Australia.

Sex-Specific Patterns in Abundance, Temporary Emigration and Survival of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in Coastal and Estuarine Waters

“…Some cetacean species are sexually dimorphic in size, but this is not obvious in the field (e.g., the common bottlenose dolpin, Tursiops truncatus, Tolley et al, 1995), or are sexually monomorphic in size, shape and appearance (e.g., the Indo-Pacific bottlenose dolphin, T. aduncus, Hale et al, 2000;Kemper, 2004). The sex of an individual can be documented through several techniques, including molecular sexing (Gilson et al, 1998); laser photogrammetry (Rowe and Dawson, 2009); underwater photography (Webster et al, 2009); opportunistic observations of the genital area (Morteo et al, 2014); or, for females, repeated close association with a calf (Mann, 2000).…”

Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia

“…Tursiops taxonomy is unresolved and at present T. truncatus (Montagu, 1821) and T. aduncus (Ehrenberg, 1833) are recognised in the Indo-Pacific region (Rice 1998;Kemper 2004). In Australian waters, until recently, all Tursiops were recorded as T. truncatus (Ross and Cockcroft 1990;Charlton-Robb et al 2011); however, T. aduncus is now known to occur in estuarine and coastal waters of eastern Australia (Möller and Beheregaray 2001;Fury and Harrison 2008).…”

Genetic differentiation in bottlenose dolphins from South Australia: association with local oceanography and coastal geography

“…In South Australia (SA), the taxonomic status of coastal bottlenose dolphins Tursiops sp. has not yet been clarified (though see Kemper 2004). Recent genetic evidence, based on both mtDNA and microsatellite data, strongly suggests that coastal bottlenose dolphins from SA, Victoria and Tasmania are evolutionarily distinct from the 2 other recognised bottlenose dolphin species (Charlton et al 2006, Möller et al unpubl.…”