Certain adult pufferfish have a parrot like 'beak' with a distinct cutting edge. This beak is formed by bands of dentine which continually grow to replace those lost through feeding. In young pufferfish, the beak is not present, instead 'first-generation' teeth develop, only to be replaced by four teeth at the front of the jaw which subsequently make-up the beak structure.
Figure 1: A, the freshwater pufferfish, Monotrete abei. B, side-view
showing the large lips covering the beak. C & D, views of the beak itself.
Photo courtesy of Fraser et al (2012: 2)
According to Dr Gareth Fraser, who led the project, investigating the manner and mechanisms of tooth replacement is of "great interest for science... to understand the genes that govern the continued supply of teeth and mechanisms of dental stem cell maintenance."
Humans only replace their teeth once, in childhood. Unlike a shark with its many rows of teeth, or a rat with it's continually erupting ones, humans cannot replace teeth naturally. The much increased longevity of modern human populations is therefore at odds with the single set of trauma-and-disease-prone adult teeth they have. Dr Fraser believes that the knowledge could eventually be used to "facilitate advances in dental therapies" with this in mind.
Fraser, GJ, Britz, A, Johanson, Z and Smith, M. 2012. Replacing the first-generation dentition in pufferfish with a unique beak. PNAS.
Available at: http://www.pnas.org/content/early/2012/05/04/1119635109.full.pdf+html
University of Sheffield press release.
Available at: http://sheffield.ac.uk/mediacentre/2012/pufferfish-gareth-fraser-natural-history-museum-evolution-denistry.html