Fibonacci

Shells often have "equiangular" growth. That is, they grow in a spiral with continuous exponential growth which gives a constant angle between the direction of the curve and the tangent to a circle touching that point, which is centered on the start of the spiral. The Golden Spiral is equiangular, but shells can grow at many different rates, not just the one that produces the Golden Spiral. So just as with the bird's talon, it is wishful thinking to see shells as an example of Fibonacci in nature.