Rodents as indicators of the climatic conditions during the Middle Pleistocene in the southwestern Mediterranean region: implications for the environment in which hominins lived.

Rodents are a very useful tool in reconstructing the environment of the past, especially owing to their rapid response to climate change, their small home range, and their restricted habitat requirements. They are a highly diverse group of mammals, which have high reproduction rates and as a result can evolve rapidly. The abundance of their microfossil remains in archaeological and paleontological sites permits robust statistical analyses to reconstruct the past climate and environment. Recently, a number of studies have affirmed the need to deepen the climatic characterization of the European Quaternary, the Middle Pleistocene being an important stage for ascertaining how our hominin ancestors lived. The aim of this study is to characterize the climatic conditions in which hominins lived in southwestern Mediterranean Europe during the Middle Pleistocene. To reconstruct these climatic conditions, we apply the bioclimatic model to rodent assemblages from Middle Pleistocene sites with human remains (Caune de l'Arago, Sima de los Huesos, Aroeira cave, Visogliano, Trinchera Galeria, and Mollet cave). Based on the percentage distribution of the species in different climate types and applying multiple linear regressions, we estimated the mean annual temperature, the mean temperature of the coldest month, and the mean temperature of the warmest month. We compared these estimates with data collected over the last 30 years from nearby meteorological stations to obtain the differences with current climate and observe the fluctuations. The climatic conditions obtained from the results of this study show that, while in Iberia mild climatic condition prevailed, in southern France and northeastern Italy harsher weather conditions were indicated.

Pleistocene history of Iberomys, an endangered endemic rodent from southwestern Europe.

The extant Cabrera's vole, Microtus cabrerae, differs in morphology and evolutionary history from the other species of Microtus. This arvicoline has unique derived features in the cranium, mandible and dentition. Probably its most conspicuous features are its large size, the high skull in lateral view, the long and distally broad nasals, and the triangle shape of the anteroconid complex, with a marked labio-lingual asymmetry of the occlusal surface of the first lower molars. In this study, we propose a phylogenetic lineage that includes Cabrera's vole in what until now has been the Microtus subgenus Iberomys. Paleontological information and several life history traits support the elevation of Iberomys to the rank of genus. Genus Iberomys comprises species that have appeared in succession during the Quaternary: in the Early Pleistocene, the extinct I. huescarensis in the Middle Pleistocene, the extinct I. mediterraneus and in the Late Pleistocene, the extant I. cabrerae. Interestingly, the extant species shows several biological singularities, such as multiple polymorphic copies of the SRY male-specific gene in both males and females, and the lowest basal metabolic rate in relation to weight among arvicoline species. Likewise, its habitat requirement is unique among the Iberian arvicolines. Accordingly, the biological and paleontological data that we present in this work support the elevation of its taxonomic rank to that of genus. This study also suggests a modification of nomenclature: Microtus (Iberomys) brecciensis is replaced with I. mediterraneus and the common name of the extant M. (I.) cabrerae changed from 'topillo' to 'iberon' to improve conservation and protection actions.