A model for the Holocene extinction of the mammal megafauna in Ecuador

This paper presents the results of multidisciplinary research in the Ecuadorian coastal regions, with particular emphasis on the Santa Elena Peninsula. The new evidence, together with previous data gathered on the Ecuadorian cordillera during the last 12 years, allows us to formulate a model that accounts for most of the mammal megafauna extinction at the Pleistocene/Holocene transition. After the illustration of geomorphological and paleontological evidences of the area of the Santa Elena Peninsula (and other sites), and of a summary of the paleoclimatic data, the main results and conclusions of this work are: (1) Late Pleistocene mammal assemblages survived in the Ecuadorian coast until the Early Holocene sea level rise; (2) Prior to the extinction of most of the megafauna elements (mastodons, ground sloths, equids, sabre-tooth felids), the mammal communities at Santa Elena Peninsula comprise elements with differing habitat requirements, attesting conditions of high biological pressure; (3) At the El Cautivo site (Santa Elena Peninsula), we have discovered Holocene sediments containing the first known occurrences in Ecuador of lithic artifacts that are associated with mammal megafauna remains; (4) During the last 10,000 years, the coastal region of Ecuador underwent significant changes in vegetation cover. At the Pleistocene/Holocene transition the climate changed from very arid conditions to humid conditions. Our data indicates that the megafauna definitively abandoned the Cordillera areas around 12,000 yr BP due to t he increasing aridity, and subsequently migrated to coastal areas where ecological conditions still were suitable, Santa Elena Peninsula and mainly Amazonian areas being typical. We conclude that the unusual high faunal concentrations and the change to dense vegetation cover (due to a rapid increase in precipitation in the lower Holocene) at 8000–6000 yr BP, caused the final collapse and extinction of most elements of the mammal megafauna. Vegetation cover in the area of Santa Elena should have been extensive, and even more so in the Guayas and Guayabamba valleys. The newly densely vegetated areas, and fluvial barriers, transformed the refugia into lethal traps for large animals already under biological stress, such as were mastodons, ground sloths and equids. Within the megafauna, only tapirs and artiodactyla (Cervidae and Camelidae) survived. In our opinion, the most suitable model to justify the great crisis of the mammal megafauna at the Pleistocene/Holocene transition, also in areas out of Ecuador, must be mainly based on the three parameters: high aridity, high humidity and geographic factors.