Eomys

Abstract: Eight rodent species from the Upper Oligocene of Pareja are described. The Theridomyidae are represented by Issiodoromys minor and Archaeomys (A.) gervaisi and the Eomyidae by Eomys cf. molassicus. Four cricetid species are described: Heterocricetodon landroveri sp. nov., Eucricetodon margaritae sp. nov., Eucricetodon cf. atavus, and Eucricetodon sp. One new glirid species, Gliravus caracensis, is recognized. The fauna of Pareja is considered to be somewhat older than that of Carrascosa del Campo, and considerably younger than that of Montalban.

Abstract: Until now there have been no definitive reports of eomyid rodents in the Tertiary of Asia, although their discovery there has long been expected. Four forms of eomyid rodents (Eomys orientalis, sp. nov., Eomyodon sp., Pseudotheridomys asiaticus, sp. nov., and ?Pseudotheridomys sp.) are now recognized in the Oligocene of Nei Mongol, China. These occurrences support the hypothesis of exchange between the European and North American eomyids via Asia. The beds bearing Pseudotheridomys asiaticus and ?Pseudotheridomys sp. at Loc. 77048 appear to be slightly younger than the classic localities at Saint Jacques. The Tertiary deposits at Saint Jacques appear to include at least two horizons: late middle Oligocene and late Oligocene or latest middle Oligocene.

Abstract: New material of eomyids from the very Early Oligocene of southern Germany and the late Early Oligocene of France and Spain has been studied. In Germany besides the previously known and unique Eomys antiquus (Aymard, 1853), two other species have been found including an undetermined genus, Eomyidae gen. et sp. indet, with unexpected morphological features that were considered as derived based on our current knowledge. These three species show that at least three immigrant lineages were present as early as the beginning of the Oligocene in Europe. In France and Spain, except for Eomys antiquus which confirms its large geographical distribution, the species found are unlikely to have evolved from the German ones, thus suggesting another immigration wave of eomyids in Europe. Finally, the diversity of the first European eomyids is higher than expected, leading us to consider a more complex evolutionary history than a simple radiation from Eomys antiquus as previously proposed. Despite the limited material available, the undetermined genus, here considered as a likely new genus, shows some clear morphological affinities with the Asian late Oligocene genus Asianeomys Wu, Meng, Ye & Ni, 2006, thus suggesting a possible common Asian ancestor.

Abstract: The analysis of oxygene isotope variations as well as paleobotanical data suggest that the Oligocene/Miocene boundary corresponds to a transitional period marked by floristical and climatic variations. During this period, the pyreneo-alpine tectonics has contribued to modify the geography and western Europe landscapes. Faunal changes (appearances, extinctions, migrations) are observed in different mammalian groups, notably in the rodents. A study of the evolutionary trends and patterns in paleogene rodents is involved for the period ranging from level MP 28 of the Late Oligocene to the Early Miocene, including the Oligo-Miocene boundary. The Rodents fauna from the sites of Venelles (Bouches-du-Rhone District, France) and Thezels (Lot, France), previously mentionned in litterature, have been studied. The first description of the Eomyidae of La Milloque (MP 29) has been completed. These faunas are compared to those from various localities dating from the considered period. In La Milloque, a new representative of the Eomys species is described next to a form close to Rhodanomys hugueneyae ENGESSER, 1987. It is the Eomys milloquensis nov. sp., the likely descendant of Eomys quercyi COMTE & VIANEY-LIAUD, 1987. Two new species are also described in Thezels: Eucricetodon thezelensis nov. sp., resulting from a likely and local evolution of Eucricetodon praecursor (SCHAUB, 1925) from La Milloque, which, in the same geographic area, could be at the origin of Eucricetodon hesperius ENGESSER, 1985 from Paulhiac. Plesiosminthus admyarion nov. sp., quite distinct from Plesiosminthus schaubi VIRET, 1926, which announces Plesiosminthus myarion SCHAUB 1930. Venelles'Plesiosminthus schaubi population is considered as a sub-species, named Plesiosminthus schaubi meridionalis nov. subsp. New phylogenetic patterns are proposed. Among the Eomyidae, a quantification of various features of the M 1-2 crown (hypsodonty, degree of abrasion, occlusal angle, state of development of the I and V anticlines), and a comparison with the occlusal diagram of the other teeth among various other populations allows a more efficient separation of Eomys and Rhodanomys genera. In Western Europe, and within this period, it finally does not seem possible to gradually connect the genus Eomys to the genus Rhodanomys. The evolution of the Eomys quercyi - milloquensis lineage seems to underline a similar evolution to that which may have led from the Eomys to the Rhodanomys form. The latter which appears totally accomplished at level MP 29 of the Oligocene is considered as an immigrant. If we compare the most representative species of the Venelles, Thezels, and Coderet sites, (i.e. Rhodanomys, Eucricetodon, Adelomyarion, Peridyromys, Plesiosminthus), it becomes impossible to confirm their biochronological separation. The noticeable differences between the populations may be interpreted as geographical variations. An explanation to these variations, and to fauna's evolution during the Late Oligocene and Early Miocene can be found in the environmental modifications, supported by isotopic, paleobotanical and sedimentologic analysis. A tentative reconstruction of the environments is attempted by,the cenogram method.