For about a century, scientists have questioned the identity of a dolphin inhabiting the coastal waters off southeastern Australia. Their suspicions were confirmed last week, when a team of researchers in Australia reported that the dolphin, long classified as Tursiops truncatus, one of two recognized species of bottlenose dolphin, in fact represents a previously unknown third bottlenose species, Tursiops australis.
The researchers, who published their work in the journal PLoS One and proposed that the new species be given the name Burrunan dolphin, verified that the dolphin is in fact a new species using a combination of techniques. For example, analysis of mitochondrial DNA, which has a high mutation rate allowing scientists to discern a species' ancestry, revealed an evolutionary divergence between the Burrunan dolphin and the other two species of bottlenose dolphins. The genetic evidence was supported by observations of a distinct pattern of tri-coloration in the Burrunan dolphin, as well as a distinct combination of body size, cranial features, and rostrum (beak) and dorsal fin morphology.
In the paper describing the new species, the researchers discuss the unified species concept, an idea introduced in 2007 by zoologist Kevin De Queiroz from the National Museum of Natural History at the Smithsonian Institution. Scientists typically define species based on one of several different species concepts. For example, the biological species concept defines species based on reproductive isolation (or their inability to interbreed with other species), and the phenetic species concept defines species as sets of organisms that look similar. The unified species concept, however, is based on the idea that spatially separated populations of species are headed in different evolutionary directions, and therefore evidence of divergence, whether morphological, genetic, or behavioral, is relevant in defining species.
Prior to the new research, the Burrunan dolphin was thought to be a metapopulation (a geographically separate population) of T. truncatus. In fact, in the early 20th century, the smaller Burrunan was believed to represent the female version of T. truncatus, and the discovery of large and small specimens was used as evidence of sexual dimorphism in bottlenose dolphins. But in the ensuing decades, researchers realized that the larger dolphins were found primarily in offshore waters, whereas the smaller dolphins were found mainly in semi-enclosed bodies of water. Their ranges overlapped only in some areas.
In recent years, the taxonomic position of the smaller form became increasingly suspect, having been described in the early 2000s as both T. truncatus and T. aduncus and even simply as Tursiops sp. But with multiple lines of evidence indicating that the Burrunan dolphin is unique from other bottlenose species, the latest research may finally bring the debate to an end.
The naming of a new species of dolphin marks an exciting discovery and brings the number of known dolphin species close to 40. More than 1.7 million species, including plants, animals, and fungi, have been described, but scientists estimate that many more are awaiting discovery. And while we might wonder where these unknown species are lurking, as the discovery of the Burrunan dolphin suggests, they may be right in front of us.
Kara Rogers is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is a member of the National Association of Science Writers and author of Science Up Front on the Britannica Blog. She holds a Ph.D. in Pharmacology/Toxicology, but enjoys reading and writing about all things science. You can follow her on Twitter at @karaerogers.
This post also appears on the Britannica Blog.