How Sharks got their teeth
Research looks at the evolution and development of shark teeth and considers a point in time when their teeth were used as taste buds as well as for the consumption of food.
What we’re researching
Recent research at Birkbeck, in collaboration with the Natural History Museum, King’s College Dental School and University of Sheffield, has sought to investigate the evolution and development of shark teeth, looking at embryonic development, different growth stages and examples from the long shark fossil record.
While the teeth of bony fish, reptiles and mammals develop within the jaw bones, those of sharks and rays lack true bones and have teeth embedded in the skin. The teeth form in a groove on the inside of the jaw, with each tooth moving up to the jaw edge in a conveyor belt of skin, before being shed when the tooth is blunt or damaged.
As a result, sharks have disposable teeth, producing many thousands in their lifespan, and allowing them to have sharp and slender teeth impossible in any animal, such as a mammal, that cannot rapidly replace its teeth. Each tooth position on the jaw becomes a succession of teeth, forming as a production line with parts of the tooth (first the outside, then the inside, then the root) added as the tooth moves towards the edge of the jaw. As teeth are lost, there is a mechanism to ensure there are always enough teeth in their functional position, with the positions of adjacent teeth alternating along the length of the jaw.
Dr Charles Underwood, Lecturer in Palaeontology in the Department of Earth and Planetary Sciences, said, "Our research enables us to look at how teeth have developed in all vertebrates with the knowledge that the same genes control the development of their teeth. However, the teeth of sharks and rays appear to be unique amongst vertebrates. Not only does the shark offer a study system for whole unit dental regeneration, it also represents an important model for understanding the evolutionary context of vertebrate tooth regeneration."
“...The teeth of sharks and rays appear to be unique amongst vertebrates. Not only does the shark offer a study system for whole unit dental regeneration, it also represents an important model for understanding the evolutionary context of vertebrate tooth regeneration.”
What the impact will be
Intriguingly, the gene control on the initiation of the teeth deep in the mouth is the same as that in the nearby developing taste buds. This may suggest that deep in their evolutionary history, teeth were taste buds with the same structure, some becoming mineralised to help with food gathering, and others being filled with nerves to help with consuming food. It is also evident that the same genes control the formation of teeth in sharks, as in other vertebrates, despite their structure and formation being very different. So whilst teeth may have evolved on two (or more) separate occasions from other structures, the overriding control is the same in all and suggests that the genes used in forming teeth were present in the very earliest vertebrates, before sharks and bony fish diverged and long before teeth (and possibly jaws) appeared. This therefore fundamentally impacts on how we perceive vertebrate evolution.
This research area is now expanding to include study on the mineralisation of the shark skeleton in relation to both their evolution and ecology.
Further Information
Watch a Birkbeck Explains video on How Sharks got their teeth.