2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/28196We introduce a new model for large scale evolution and extinction in which species are organized into food chains. The system evolves by two processes: origination/speciation and extinction. In the model, extinction of a given species can be due to an externally induced change in the environment or due to the extinction of all preys of that species (co-extinction). The model is able to reproduce the empirical observations, such as the statistical fractality of the fossil record or the scale-free distribution of extinction events, without invoking extinctions due to competition between species.5 pages, 8 ps figures, using Latex2e with epsf rotate and multicol style filesStatistical MechanicsDisordered Systems and Neural NetworksQuantitative Biologytext