Young pufferfish have a set of two rows of normal fish teeth but their subsequent teeth become fused to form a beak— pictured here in this specimen of the Globe pufferfish (Tetraodon lineatus). Although anatomically different from teeth, the mechanism of beak development in pufferfish is the same as the stem cell-based one all vertebrates have used for 400 million years to build teeth. Such evolutionary developmental novelties as the beak of the pufferfish have allowed scientists to gain novel insights into the mechanisms of tooth development and loss in humans.

For more surprising pufferfish facts watch Microbe Minute—part of I Contain Multitudes

https://www.youtube.com/channel/UCnZK1E7WoLpFNIHHChgVMtw

Technical Details: Tetraodon lineatus is a freshwater pufferfish, native to major African river systems, and feeds on molluscs. They can grow to half a metre long and their beaks need to be big enough (up to 10cm wide) to crush hard shellfish. The image was taken at the Natural History Museum, London, UK by Dr. Ralf Britz.

Credit: Gareth Fraser, PhD, Department of Animal and Plant Sciences, University of Sheffield, UK. and Ralf Britz, PhD, Department of Life Sciences, Natural History Museum, UK.

Links: http://www.fraser-lab.net

http://www.nhm.ac.uk/our-science/science-news/2017/may/pufferfish-beak-originates-from-stem-cell-tweak.html

http://now.tufts.edu/articles/promise-growing-new-teeth