Late Pleistocene vertebrate assemblages from Artazu VII and Artazu VIII sites (Arrasate, northern Iberian Peninsula): palaeobiology and palaeoecology

Abstract

The Late Pleistocene was a period characterized by numerous climatic fluctuations that occurred in millennial scale alternating cold and warm moments. Unfortunately, Late Pleistocene palaeontological sites without human intervention are limited in the Iberian Peninsula, and even more those with good state of preservation and rich taxa diversity. Thus, two new vertebrate fossiliferous localities are presented in this thesis: Artazu VII and Artazu VIII. Both sites were discovered after a blasting at Kobate Quarry (Arrasate, northern Iberian Peninsula). The good integrity and good state of preservation of large mammal bones, as well as the lack of anthropological or predator activity, discarded the possibility of an anthropogenic origin for both sites.This thesis constitutes a compilation of different types of studies, all of them focused on the reconstruction and evolution of the environment during Late Pleistocene. The stratigraphic sequence has been correlated to Marine Isotopic Stages (MIS), taking into account Radiocarbon (AMS) and Amino Acid Racemization (AAR) datings and the palaeoenvironmental variations inferred from the small vertebrates community. In addition, we compare these results with the information available for the same periods at other sites in the Iberian Peninsula.- Artazu VII site was discovered in 2012 and excavated in 2013 by an emergency excavation. There were no clear stratigraphic sequence or levels, and AMS and ARR datings situated the site in ~ 93 ka BP. The fossiliferous record (small mammals, amphibians, reptiles, ungulates, carnivores and birds) suggested the existence of large forested areas with some grassland and a water course nearby, within a notably warm and humid climate. Indeed, regarding woodland expansion and retraction, four climatic main phases were observed. These palaeoenvironmental conditions, combined with dating results, suggest that the deposit from Artazu VII would be located in the first half of the Late Pleistocene, in the MIS 5c.- Artazu VIII site was found in 2013 and the excavation was carried out in the following two years. Based on sedimentological features, 12 levels were differentiated along the sequence. According to AMS and ARR datings, the sedimentary fill was a continuous succession that comprises, at least, 36 ka of the late Pleistocene. The small and large mammal assemblages and the preserved bird community, as well as the mineralogical and sedimentological studies, allowed the approach to the palaeoclimatic conditions and the evolution and sedimentary fill origin of this cave. Three palaeoenvironmental and palaeoclimatic stages were differentiated and correlated to NGRIP 18O curve, from MIS 5c to MIS 4.