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Résumé: Des fouilles récentes dans l'Éocene supérieur de Zambrana (Alava, Pays basque) ont livré des restes de vertébrés continentaux, les premiers découverts dans le bassin tertiaire de Miranda-Treviño. L'association fossile est composée de tortues (Chelonii indet.), crocodiliens (Diplocynodon sp.) et mammiferes, qui comprennent de possible insectivores (Lipotyphla indet.), carnivores (cf. Quercygale sp.), rongeurs (Theridomys aff. golpei, Elfomys aff. parvulus, Pseudosciurinae indet., Glamys priscus), artiodactyles (Xiphodontidae indet.) et périssodactyles (Paranchilophus sp., lagiolophus aff mazateronensis, Palaeotherium sp.). L'association de rongeurs et de périssodactyles suggere un age ludien (Priabonien) moyen-inférieur, correspondant a la biozone MP 18. La faune de mammiferes de Zambrana est comparable aux faunes endémiques de l'Éocene moyen-supérieur des bassins ibériques occidentaux et centraux. Les dép6ts fossiliferes sont des marnes et des calcaires a niveaux de charbon, d'origine lacustre. L'étude géologique de la région indique que le bassin tertiaire de Miranda-Treviño a été fortement influencé par l'activité tectonique régionale et que les premiers mouvements compressifs importants liés a la phase pyrénéenne de l'orogenese alpine ont eu lieu pendant l'Éocene inférieur., Recent field work in the Upper Eocene of Zambrana (Alava, Basque Country) has yielded continental vertebrate remains, the first discovered in the Tertiary Miranda-Treviño Basin. The fossil association consists of turtles (Chelonii indet.), crocodilians (Diplocynodon sp.) and mammals, including possible insectivores (Lipotyphla indet.), carnivores (cf. Quercygale sp.), rodents (Theridomys aff golpei, Elfomys aff. parvulus, Pseudosciurinae indet., Glamys priscus), artiodactyls (Xiphodontidae indet.) and perissodactyls (Paranchilophus sp., Plagiolophus aff mazateronensis, Palaeotherium sp.). The association of rodents and perissodactyls suggests an early middle Ludian (Priabonian) age, which corresponds to the biozone MP 18. The mammalian fauna of Zambrana is like the middle Upper Eocene endemic faunas from the western and central Iberian basins. The fossiliferous beds are lacustrine coal-bearing marls and limestones. The geological study of the area evidences that the Tertiary Miranda-Treviño. Basin was highly influenced by tectonic activity, and that the first compressive stresses related to the Pyrenean phase of the Alpine orogenesis took place during the early Eocene.

The changes in the distribution of the small mammals associations of the Pleistocene of Spain are used here tomake an environmental interpretation from this age to the present. We have taken into account the paleoenvironmental significance of some micromammals (Rodentia, Lagomorpha, Insectivora and Chiroptera), whose living representatives live in restricted habitats, as well as their evolution, immigration and extinction. Our observations allow the following remarks. After the relative cooling that happened by the late Pliocene and at the beginning of the Pleistocene, Spain was subjected to a mild climate since the Middle Pleistocene to the present. Some relatively warmer phases probably ocurred in the Middle Pleistocene, as well as some cooler phases during the glaciations of the Upper Pleistocene, even if these were less intense than in the rest of Europe. Humidity was probably greater during the Late Pliocene and the Lower Pleistocene than in preceding ages in Southern Spain. The relatively warmer phases during the Middle Pleistocene could have also been more humid in all the Peninsula, probably with an inceease of the water courses and a greater extension of the vegetation cover. The milder phases during the Upper Pleistocene would also be more humid with more wooded areas, while the cooler phases were possibly drier. There are evidences of a tendency towards a drier climate since the Upper Pleistocene until the present. As a result, a progressive decrease in the diversity of the micromammals happened which still prevails nowadays mainly in the Mediterranean area of Spain.