A NEW METHOD FOR EVALUATING THE CONVEXITY OF MORPHOLOGICAL CHARACTERISTICS

Convexity is an important type of morphological data in both paleontology and organismal biology. A new method to determine convexity is reported to assign a numerical value to the convexity of morphological characteristics. This method is applied to the plates that make up the calices of crinoids. By photographing calyx plates in a cross-sectional view, it was possible to obtain a shape that could be approximated by a parabola. The cross sectional plate image is then imported into MATLAB where an approximated parabola is plotted. It is then possible to obtain the second derivative of this parabolic curve by differentiating twice across it. The value of this second derivative is the convexity value of the plate. With a numerical value assigned to convexity, it is possible to easily use this value in statistical tests and other quantitative biological methods. This new method is important because it is a cost effective and easy way to determine a measure for the convexity of morphological characteristics.