1. Department of Petrology and Geochemistry; Universidad Complutense; c/José Antonio Novais 2 28040 Madrid Spain
2. Department of Geology and Geochemistry; Faculty of Sciences; Universidad Autónoma de Madrid; 28049 Madrid Spain
3. Department of Geology; Universidad de Salamanca; Escuela Politécnica Superior de Avila 05003 Avila Spain
4. Department of Palaeobiology; Museo Nacional de Ciencias Naturales-CSIC; c/José Gutiérrez Abascal 2 28003 Madrid Spain