6 How Did Past Environmental Change Affect Carnivore Diversity and Home-Range-Size in Spain? María T. Alberdi 1 , José L. Prado 2 , Esperanza Cerdeño 3 and Beatriz Azanza 4 1 Departamento de Paleobiología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, 2 INCUAPA, Departamento de Arqueología, F.C.S., Universidad Nacional del Centro, Olavarría, 3 Departamento de Paleontología, IANIGLA, Centro Científico Tecnológico CONICET, Mendoza, 4 Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Zaragoza, 1,3 Spain 2,4 Argentina 1. Introduction An important aspect of evolutionary biology is to know the faunal diversity changes through time. There is a general agreement that the knowledge of evolutionary patterns through time from an ecological perspective provides information that is not available from ecological studies on extant faunas (Vrba, 1985, 1995a; Behrensmeyer et al., 1992; Jablonski, 2005). Iberian Cenozoic basins provide an exceptional record of fossil mammals and continental environments, giving a great opportunity to evaluate the ecological and evolutionary responses of mammalian communities to climatic changes through the last millions years (Azanza et al., 1999, 2000; Hernández Fernández et al., 2007; Van Dam et al., 2006). This knowledge is essential for linking the dynamics of biotic change from ecological to evolutionary time scales and for understanding the processes that transform ecosystems over geologic times (Badgley et al., 2008). Previous works have proposed different explanations for biodiversity changes through time, emphasizing the influence of both physic and biotic factors (e.g., Van Valen, 1973; Janis, 1989; Stucky, 1990; Vrba, 1995a, 1995b, 2000; Prothero, 1999, 2004; Alroy, 2000; Alroy et al., 2000; Barnosky, 2001, 2005; Vrba & DeGusta, 2004). The response of mammals throughout the late Cenozoic has been often reflected by migrations or variation of their area of distribution, related to the vegetation cover and latitudinal displacement of biomes. Patterns of change in the home range size (HR, the size of the minimum area that can sustain the individual’s energetic requirements) through time can provide important insights into the ecological and evolutionary responses of mammalian communities to new environmental conditions. In a lesser degree, mammals can also respond evolving into new species. These events could modify the structure of mammalian communities, triggering new internal