Burrunan dolphin

The Burrunan dolphin (Tursiops australis) is a proposed species of bottlenose dolphin found in parts of Victoria, Australia first described in 2011. Its exact taxonomy is debated: numerous studies support it as being a separate species within the genus Tursiops and occupying a basal position within the genus, with limited phylogenetic studies using different methodologies indicate that it is a subspecies of the Indo-Pacific bottlenose dolphin (Tursiops aduncus). The Burrunan dolphin is not currently recognized as a species by the Society for Marine Mammalogy or American Society of Mammalogists, which cites problematic methodology in the original study proposing species status and recommends further research.

There are only two known resident populations in Victoria, Australia, with an estimated total population size of less than 180 individuals, and the predicted effective populations sizes small; Port Phillip Bay: 81.5, Gippsland Lakes and Tasmania: 65.5.

Prior to proposal of the name T. (aduncus) australis, the term "Tursiops species, southern Australian bottlenose dolphin (SABD)" had been used.

The Burrunan dolphin has had a heavily debated taxonomy. It was formally named Tursiops australis by the researcher who described it, Kate Charlton-Robb of Monash University, and colleagues. The dolphin's common name, Burrunan, is an Aboriginal name in the Boonwurrung, Woiwurrung and Taungurung languages, meaning "large sea fish of the porpoise kind". The name australis is the Latin adjective "southern", and refers to the Australian range of the dolphin. It was the third time since the late 19th century that a new dolphin species had been recognised.

Some differences had previously been noted prior to its description, but for a long time not enough evidence was available to classify it as its own taxon. An examination of their skulls, external characteristics, and DNA from old and current samples revealed unique characteristics supporting its classification as a separate species. However, later studies either supported or disputed these findings.

In March 2020, the Canadian Journal of Zoology published "Taxonomy and distribution of bottlenose dolphins (genus Tursiops) in Australian waters: an osteological clarification" by Maria Jedensjö et al., which questioned the classification of T. australis as a distinct species. The study conducted a comprehensive osteological survey on the skulls of 264 dolphins using 2D and 3D morphometrics, and found that the Burrunan dolphin fell well within T. truncatus using both techniques. However, a larger body of evidence still exists to validate the Burrunan as a species using mtDNA regions, concatenated mtDNA/nuDNA sequences, the mitogenome, and more recently the time-calibrated molecular phylogeny of Artiodactyla.

In May 2020, a separate phylogenomic analysis that used a double digest RADseq protocol (in contrast to the previous studies, which used whole mitogenomes) found that the South Australian form of the Burrunan dolphin fell within T. aduncus, forming a monophyletic lineage that is sister to an undescribed, wider coastal Australasian subspecies. Samples from the original species description, including the holotype of the species, from Victoria and Tasmania, were not included in this study. The same study also disputed the alleged polyphyly between Tursiops and Stenella found in previous studies, finding this to be a consequence of reticulate evolution in Tursiops (including past introgression from Stenella) and incomplete lineage sorting in the studies. The American Society of Mammalogists has followed the results of this study and now classifies T. australis under T. aduncus, although it also acknowledges the debate over its status.

The Burrunan dolphin is dark bluish-gray at the top near to the dorsal fin extending over the head and sides of the body. Along the midline, it is a lighter gray which extends as a blaze over on the side near the dorsal fin. Ventrally, it is off-white, which reaches over the eye and the flipper in some instances. By size, it is smaller than the common bottlenose dolphin, but larger than the Indo-Pacific bottlenose dolphin, measuring between 2.27 and 2.78 m (7.4 and 9.1 ft) in length.