By Carolina Loch
Animals in general use their teeth in many activities such as capturing prey, biting, chewing and defence. In most mammals, teeth differ from front to back, to give incisors, canines, premolars and molars. As a rule, the shape of teeth is related to the animals’ diet. In dolphins, on the other hand, teeth are usually all the same (homodont dentition) – a simple cone – with many more teeth than in typical mammals. Some species of dolphins can have more than 200 teeth. Humans, in comparison, commonly have 32 (but only if your four wisdom teeth erupt).
Most mammals use their teeth primarily for cutting and chewing food, however dolphins’ teeth are mainly used for piercing and grasping, as food items are swallowed whole. Dolphins are carnivores – they eat flesh. Most dolphins feed on fish, but some may also prey on animals such as squids, shrimps and crabs.
By studying teeth of animals we can learn not only about their feeding habits, but also about their evolution and relationships among species. Teeth may help us to understand the influences of the environment in which they live and even allow us to estimate their age quite precisely. That’s why teeth are an important tool for scientists studying the biology of dolphins and other mammals.
While studying teeth of different dolphin species from South America, my colleagues and I discovered that those animals presented several pathologies and abnormal conditions in their teeth – similar to the ones that make us fear sitting on a dentist chair! Diseases and pathologies that affect the teeth of humans and domestic animals have been widely studied and reported in the scientific literature. But the same is not true for dolphins – maybe because they don’t go to the dentist. Normally they don’t live under human care and people are not looking at the state of their teeth. But these pathologies were always there, waiting to be discovered!
My studies led to a long-term project that became theme of my BSc. and MSc. theses and recently a publication in the journal Diseases of Aquatic Organisms (http://www.int-res.com/abstracts/dao/v94/n3/p225-234/). My colleagues and I used 27,559 teeth and 348 skulls from 10 species of dolphins in scientific collections from Southern Brazil, including bottlenose and estuarine dolphins as well as the killer whale. We discovered that conditions such as caries cavities, calculus deposits, surface staining and acid erosion existed in dolphins. These pathologies were not exclusive to us and other animals that normally feed on processed and altered food.
We now know that dolphins show dental pathology, but there are still many questions to be answered. For example, we still don’t know how caries cavities are formed in dolphins. In humans, caries occur because of fermentation of sugar on the surface of our teeth. How can carnivorous animals have caries as well? Is there any source of carbohydrates in their diet, or is the process of caries formation different in dolphins? There are similar intriguing questions to be asked about acid erosion. In humans, this condition is normally related to some eating disorders such as bulimia and anorexia, as well as to consumption of soft drinks and acidic juices. These causes seem plausible for us, but how can we explain acid erosion in wild dolphins?
For me, the research on dolphin teeth has shown several things. First of all, we don’t know as much about the biology of dolphins as we might think. Second, there remains much to be discovered. Third, and most importantly, science can be much improved if we work in interdisciplinary areas. Without combining our knowledge of different areas such as biology, zoology and odontology, we wouldn’t understand the processes, causes and consequences of pathological conditions in wild species.
If you’re interested in this topic and are searching for more information, please take a look at: Loch C, Grando LJ, Kieser JA, Simões-Lopes PC (2011) Dental pathology in dolphins (Cetacea: Delphinidae) from the southern coast of Brazil. Diseases of Aquatic Organisms 94:225-234.
Fig. 1 – Skull of a bottlenose dolphin (Tursiops truncatus) showing its multiple conical teeth. Photo by Carolina Loch.
Fig 2 – Some examples of dental pathologies diagnosed in dolphins. Calculus deposits in the bottlenose dolphin Tursiops truncatus (A) and acid erosion in the estuarine dolphin Sotalia guianensis (B). Photos by Carolina Loch.
Fig.3 – Analyzing pathologies in teeth and mandibles of a false killer whale (Pseudorca crassidens). Photo by Ignacio Moreno.