Análisis bioclimático y paleoecológico de las faunas de roedores del Mioceno Medio Superior ibérico

Resumen

Resumen: This PhD Thesis focuses on Miocene rodent communities from the Iberoccitanian Region (SW Europe). The study of extinct species of this group enabled us to establish an accurate biochronological scheme, furthermore the information obtained by the study of their extant relatives enabled us to infer changes in climatic parameters through time and by the use of geometric morphometric techniques to obtain more accurate data than previously reported about the ecological preferences of this mammalian group. This PhD Thesis has been structured as a compendium of an introduction, followed by five chapters presented as individual research articles and ending by a general conclusion as integration of these five chapters. The introduction makes a general overview of the main topic of this PhD Thesis: the inference of past climates and environments by the study of past rodent communities and the implementation of the Bioclimatic Analysis as an accurate palaeoclimatic inference methodology. In this section a synthesis of our knowledge on these issues is giving to the reader and the scientific motivation, justification and the particular objectives of the research were presented. The first Chapter (¿Biogeographic provincialism in rodent faunas from the Iberoccitanian Region (south western Europe) generates severe diachrony within the Mammalian Neogene (MN) biochronologic scale during the Late Miocene¿) arise by the need to establish a consistent time framework, which enables us to arrange the fossil associations according to a sequence of biotic events and subsequently to test a relationship with palaeoenvironmental changes. The nature of the continental fossil record has given rise to much controversy with regard to the establishment of general biostratigraphical scales. Additionally, biochronological scales are sometimes all that can be proposed. The primary goal of the present paper is to present a time arrangement for the Iberoccitanian micromammalian fossil sites from the latest Middle Miocene to the Mio-Pliocene boundary, spanning around seven million years (aprox. 12.61-4.95 Ma). Herein we study over one hundred faunal lists of rodents from the Iberoccitanian Region, compiled from the literature. Previous research has described two biogeographical provinces in our study area: a northern one (Vallès-Penedès and southeast France) and a southern one (all the Iberian basins, except the Vallès-Penedès). We therefore conducted Alroy¿s maximum likelihood appearance event ordination (ML AEO) methodology, applying it to the database compiled for each province. Finally, using available numerical dates for a quarter of the sites, we obtained a calibrated ordination for all localities. In each analysis, the results obtained are roughly coherent with the Mammalian Neogene units (MN) and allow estimation of the numerical ages for the entire set of fossil sites included in the study. Nevertheless, our results show severe diachrony between the two biogeographic provinces of the Iberoccitanian Region in relation to the MN boundaries, which might be linked to the existence of a refuge area associated with more humid environments in the northern province. When the biochronological frame was established, a set of palaeoecological studies was developed. In the second chapter (¿A macroecological glance to the structure of late Miocene rodent assemblages from southwestern Europe¿), a macroecological approach was developed, which enable to evaluate the relationships between climatic changes and variations in the structure of faunal communities through wide spatial and temporal scales. In this work, we applied Principal Components Analysis (PCA) to faunal data of more than a hundred rodent assemblages from the Iberoccitanian Miocene (from about 12.6 to 5.0 Ma) to achieve an objective description and understand the temporal changes in the structure of fossil rodent faunas. This analysis identified six different faunal components, which grouped genera with comparable patterns in change of species richness through time. Furthermore, it was possible to link the six faunal components in three groups based in their similar trends through time. The faunal components V and VI, for example, were formed by a set of genera with their maximum values of richness at the end of the Middle Miocene. In addition, each of these faunal components were characterised by a different set of glirids, which have different ecological preferences and this is related to its different preponderance in each province. The faunal components II and III had their maximum values of richness at the first half of the Upper Miocene. The faunal component II, the most diverse component, was mostly established by flying squirrels, which predominate in the northern province. On the other hand the faunal component III, was formed by a fewer genera. Nevertheless, these genera were the most ubiquist in the fossil sites included in this work. The last group was the set of the faunal components I and IV, which grouped the genera with maximum values of richness at the end of the Upper Miocene. The genera grouped in these faunal components were mostly murines and cricetids related to open and arid environments, associated to Messinian Crisis, which occurred at the end of the Miocene. Finally, our results indicate the existence of differential response in rodent faunas to a complex set of interconnected circumstances, including biogeographic structure of the study area and climatic changes through time. The third chapter (¿Dietary ecology of Murinae (Muridae, Rodentia): A geometric morphometric approach¿) represents a paleoecological approach developed in a more detailed scale to describe the dietary preferences of Murine rodents, which represent a highly diverse group, displaying a great ecological versatility. In the present chapter we analyse the relationship between dental morphology, on one hand, using geometric morphometrics based upon the outline of first upper molar and the dietary preference of extant murine genera, on the other. This ecomorphological study of extant murine rodents demonstrates that dietary groups can be distinguished with the use of a quantitative geometric morphometric approach based on first upper molar outline. A discriminant analysis of the geometric morphometric variables of the first upper molars enables us to infer the dietary preferences of extinct murine genera from the Iberian Peninsula. Most of the extinct genera were omnivore; only Stephanomys showed a pattern of dental morphology alike that of the herbivore genera. In the fourth chapter (¿Ecomorphological characterization of murines and non-arvicoline cricetids (Rodentia) from the Iberoccitanian latest Middle Miocene to the Mio-Pliocene boundary (MN 7/8 ¿ MN13)¿) we expand the ecomorphological study to the Cricetidae rodents and enlarge the scale to describe the biome preference of these two rodent families. These two groups, murines and cricetids are two of the largest families of mammals. Despite the greater amount of information compiled about extant rodent species, there is a lack of morphological data on dentition, which has led to them being largely overlooked in palaeoecological reconstructions. This is also due to the use of essentially different variables in ecomorphological studies of extant and extinct rodents. In order to make inferences on the environmental ranges of extinct rodent genera, we performed a phenogram based on variables derived from geometric morphometric analysis of first upper molars. This method is particularly useful in the study of the fossil record of small mammals, which is mostly represented by isolated teeth. Analysis of the first upper molars outlines was applied to murines and non-arvicoline cricetids, including both extant species and fossils from the Iberoccitanian latest middle Miocene to the Mio-Pliocene boundary. The resultant clustering of extant and extinct genera showed a predominance of ubiquitous genera among the Miocene taxa, and the presence of a few forest specialists in the two rodent groups (Murinae and Cricetidae), along with the absence of open environment specialists in either group of rodents. This appears to be related with the absence of enduring grassland biomes in the Iberian Peninsula during the late Miocene. The fifth chapter (¿Iberoccitanian Palaeoclimate from the latest Middle Miocene to the Mio-Pliocene boundary based on rodent communities: A bioclimatic analysis approach¿) made possible to describe the environmental changes during the Miocene of the Iberoccitanian Region. To develop this research we used the bioclimatic analysis, which makes possible to extract a maximum of palaeoclimatic information from the available data on mammalian palaeocommunities. In this study it was applied to a succession of fossil rodent assemblages recorded from the latest middle Miocene to the Mio-Pliocene boundary in the Iberoccitanian region (south-western Europe). It consists of both qualitative and quantitative models with the capacity to produce a detailed palaeoclimate reconstruction. We applied this method to 117 fossil rodent assemblages, comprising 215 taxa in 995 records. The climatic evolution of the Iberoccitanian region showed differences between its two biogeographical provinces during the time lapse considered. The northern province was generally characterised by more humid conditions than the southern one. In general, whereas there was a predominance of tropical biomes with a moderate dry season in the southern province, the northern one was characterized by biomes with a very short or null dry season. Additionally, our results indicated that palaeoenvironments in the southern province seem to have been conditioned by changes in hydric seasonality (wet-dry), while the northern province was driven by variations in thermal seasonality (cool-warm). This palaeoclimatic reconstruction is externally consistent and agrees with palaeobotanical and isotopic proxy-data. This work shows the possibility for an extension of the time range in which the bioclimatic analysis methodology performs adequately. Finally, at the end of this Thesis, we presented a summary of the main conclusion of each chapter, which together summarize a palaeoclimate and palaeoenvironmental report of the Miocene in an integral study of the whole Iberoccitanian Region. ¿ Palabras clave: Análisis Bioclimático, Biocronología, Bioma, Comunidades, Diacronía, Dieta, Macroecología, Mesiniense, Mioceno, Morfometría Geométrica, Paleoecología, Sinecología, Region Iberoccitana, Rodentia, Vallesiense ¿ Keywords: Bioclimatic Analysis, Biochronology, Biome, Communities, Diachrony, Diet, Iberoccitanian Region, Macroecology, Messinian, Miocene, Palaeoecology, Synecology, Rodentia, Vallesian