Evolutionary origins and development of saw-teeth on the sawfish and sawshark rostrum

Welten M, Smith MM, Underwood C, Johanson Z. 2015 R. Soc. Open sci. 2: 150189.

Professor Moya Meredith Smith, Dental Institute Professor of Evolutionary Dento-Skeletal Biology has co-authored a paper published recently on the Royal Society Open Science website. The paper explores the morphological diversity that shark and ray external skin scales can show. Skin denticles are less well understood and some of the more unusual of these are the tooth-like structures along the elongate cartilage rostrum in sawfish and sawsharks. The team used high-resolution micro-CT scanning to investigate these tooth-like structures; how they are added and replaced as the animal grows. 

Despite superficial similarity to oral teeth, these are highly modified scales, evolving independently from teeth and dentitions. This shows the extreme plasticity of the developmental module, allowing these to diversify and make structures that are called saw-teeth and are blades along the lateral margins of the rostrum saw, used in prey capture prior to feeding. 

To read the paper in full please visit the Royal Society Open Science website:

http://rsos.royalsocietypublishing.org/cgi/content/abstract/rsos.150189.

View the article on the paper on the "Science" website. 

Above is an embryo sawshark from NHM collections (Pristiophoris nudipinnis) head and part of rostrum that shows all the developing denticles under the skin. The regions are separate from each other as small skin denticles, oral teeth, and the larger saw-teeth along the lateral rostrum margins and the head region below the eye. (Drishti 3D rendered XCT scan).