COMMON DOLPHINS DELPHINUS DELPHIS IN SOUTHERN AUSTRALIA: A MORPHOMETRIC STUDY CATHERINE H. BELL, CATHERINE M. KEMPER AND JOHN G. CONRAN Bell CH, Kemper CM and Conran JG, 2002. Common dolphins Delphinus delphis in southern Australia: a morphometric study. Australian Mammalogy 24: 1-10. Examination of 211 Delphinus specimens from the coasts of Western Australia to New South Wales, including Tasmania, was conducted using 62 quantitative and 11 qualitative variables. After refining the dataset, multivariate analyses were performed on 130 cranially mature specimens using 21 cranial variables. MANOVA showed males to be slightly larger than females, but with substantial overlap, allowing analyses to combine genders. UPGMA Cluster Analysis and MDS Ordination showed three largely overlapping groups based on a size gradient. K-means analysis of these groups found no significant differences and confirmed a size gradient. Discriminant analysis of specimens grouped by geography and water depth showed a tendency for large skulls to be from coasts adjacent to deep water and small skulls from shallow water coasts. Cranial measurements were significant, postcranial measurements and features were not. Tooth counts were within the range for D. delphis for all specimens examined. This study confirms genetic evidence for a single continuously variable species (Delphinus delphis Linnaeus, 1758) in southern Australian waters. Compared with either D. delphis or D. capensis from the eastern North Pacific, the skulls of D. delphis in southern Australia were more variable for many characters. Key words: common dolphin, Delphinus delphis, skull, cranial, geographic variation, southern Australia. CH Bell, PO Box 3454, BMDC, Belconnen, ACT 2617, Australia. Email: catherine_hobart_bell@hotmail.com. CM Kemper, South Australian Museum, North Terrace, SA 5000, Australia. JG Conran, Department of Environmental Biology, University of Adelaide, Adelaide, SA 5005, Australia. Manuscript received 4 September 2001; accepted 8 June 2002. COMMON dolphins (Delphinus spp.) are in need of a worldwide systematic review due to their cosmopolitan distribution and geographic variability resulting in over 20 nominal species (Evans 1994). Heyning and Perrin (1994) studied the genus in the eastern North Pacific and reviewed the nomenclature for Delphinus, finding evidence for two species, both sexually dimorphic: Delphinus delphis, the short-beaked common dolphin, and Delphinus capensis, the long-beaked common dolphin. A parallel genetic study (Rosel et al. 1994) also found evidence for two species in that region. D. delphis was found both inshore and offshore, while D. capensis was mostly coastal (Heyning and Perrin 1994). They suggested that worldwide there were two species, with the possibility of a third, D. tropicalis, an extra long-beaked form that could be part of a cline of D. capensis in the Indian Ocean. Jefferson (in press) investigated the taxonomy of D. tropicalis, suggesting that the tropicalis-form is a long-beaked subspecies of D. capensis. His investigation found evidence for clinal variation, with hybridisation or integration between the tropicalis-form and D. capensis possibly occurring in South-east Asia and along the east coast of Africa. Jefferson describes the subspecies as D. capensis tropicalis. A pilot study by Kemper and Gibbs (1997) noted morphological variation among the Delphinus skulls from South Australia (SA). However, as the number of specimens examined in that study was small and restricted to SA, a more in-depth study was required into the nature of the cranial variation and possible taxonomic implications. A genetic study of Delphinus from southern Australia using the mitochondrial DNA control region and cytochrome b (White 1999) found no strong genetic evidence for two species and, in contrast to the results of Rosel et al. (1994), none for two species worldwide. White (1999) suggested the cranial variation noted by Kemper and Gibbs (1997) may be due to resource polymorphism. The present study investigated the nature of the differences exhibited in Delphinus skulls and skeletons from southern Australian waters, and compared them with the findings of Heyning and Perrin (1994). The study investigated the