Originally posted by Racer X 69 And why have they evolved the sawtoothed nose? Do they actually use it for something?
The theory has always been that they swim into a dense school of little fish, wag their heads side-to-side, wounding and crippling many fish, then eat them a leisure, but I think recent actual observation/research (rather than theory) has thrown considerable doubt on that interpretation of the saw's function.
ADDENDUM after some quick research
1) sawfish do sometimes wound a single prey fish with the saw, but they have apparently never been observed thrashing within a dense school of small fish.
2) sometimes a sawfish will pin prey to the bottom with the elongate rostrum before eating it, but the "teeth" on the rostrum are not used in this case.
30 The saw may be used in combat with another sawfish, or to defend against other more aggressive sharks that may actually try to eat a sawfish.
THE CURRENT MOST POPULAR INTERPRETATION OF THE SAW. The enlarged scales on the sides of the saw are not really what's important, it is simply the length of the rostrum that counts. All sharks have on their head & rostrum special receptor devices (complex to describe fully) called ampullae of Lorenzini that are electrical detectors. An electrical field is generated and detected by these devices. A fish within this field will distort it, because the electrical conductivity of a fish's body is different than that of seawater. The ampullae register the distortion which allows a shark to know that potential prey has entered the field and approximately where it is, a close enough location to guide an attack. With the ampulae of Lorenzini a shark can detect nearby prey in total darkness, in water too cloudy for vision, and sometimes below the surface of a sandy bottom (demonstrated by experiments). It is likely that the elongate rostrum of sawfish extends the ampullae of Lorenzini system, making it much larger than in typical sharks. The saw is covered end-to-end with the tiny pores of this ampullae system.