Introduction

Traditional studies of biodiversity are mainly concerned with patterns of taxonomic richness. In neontology, particularly conservation biology, the focus is generally at the species level (Reid, 1998; Mittermeier et al., 2005), while in paleontology, the genus and family levels are often used as proxies (Sepkoski, 1988; Bambach et al., 2004). However, there are of course other aspects to diversity, including genetic diversity (e.g. Petit et al., 2003) and phylogenetic diversity (Faith, 1992). A further type of diversity that has generated some interest over the past decade or so is morphological diversity, often referred to as disparity (Gould, 1991; Foote, 1997). This kind of diversity, which, importantly, does not necessarily covary with richness measures, takes as its study the variation in morphology or morphological types in a study group at a particular time or place. The focal level is generally a higher taxonomic category, such as a Family or Order, but can also be a non-monophyletic adaptive category such as carnivore or herbivore, as the object is not in the first instance to trace the evolution of a specific clade, but to investigate the range of adaptations realised by a group of organisms in a particular setting, or, in other words, the totality of their context-specific ecomorphology.

Such studies of ecomorphology can be used to investigate differences in ecological structure in time and space and help differentiate between processes such as selective or random extinctions. It leads to a much fuller depiction of biological diversity than richness alone. Ecomorphology and analysis of disparity has been used at various scales to study the diversification of vertebrates (Van Valkenburgh, 1989, 1994; Jernvall et al., 1996; Werdelin, 1996; Wesley-Hunt, 2005), invertebrates (Foote, 1994, 1997; Wills et al., 1994; Wills, 1998; Roy et al., 2001), and plants (Lupia, 1999) over their evolutionary history.