Calculating the Tempo of Morphological Evolution: Rates of Discrete Character Change in a Phylogenetic Context

Abstract

Introduction Paleontologists and biologists are often interested in the tempo of evolution: how fast or slow does evolution proceed? There are many separate components of evolution – the development and extinction of lineages, molecular change, and morphological transformation are three of the most general – and these may or may not be related to each other. Therefore, it is instructive to look at each of these separately (if possible), in order to gain a more nuanced understanding of evolutionary change. This chapter will focus specifically on morphological evolution: changes in size, shape, and discrete anatomical features and how rates of change can be calculated. Such calculations have a rich legacy in the macroevolution literature (e.g., Westoll 1949; Derstler 1982; Forey 1988; Cloutier 1991; Ruta et al. 2006; Brusatte et al. 2008a).