Olivier Maridet

Testing for Depéret's Rule (Body Size Increase) in Mammals using Combined Extinct and Extant Data

Whether or not evolutionary lineages in general show a tendency to increase in body size has often been discussed. This tendency has been dubbed “Copes rule” but because Cope never hypothesized it, we suggest renaming it after Depéret, who formulated it clearly in 1907. Depérets rule has traditionally been studied using fossil data, but more recently a number of studies have used present-day species. While several paleontological studies of Cenozoic placental mammals have found support for increasing body size, most studies of extant placentals have failed to detect such a trend. Here, we present a method to combine information from present-day species with fossil data in a Bayesian phylogenetic framework. We apply the method to body mass estimates of a large number of extant and extinct mammal species, and find strong support for Depérets rule. The tendency for size increase appears to be driven not by evolution toward larger size in established species, but by processes related to the emergence of new species. Our analysis shows that complementary data from extant and extinct species can greatly improve inference of macroevolutionary processes.

New data about the diversity of Early Oligocene eomyids (Mammalia, Rodentia) in Western Europe

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.

Proposition of dating a Miocene Alpine tectonic event using mammal biochronology: example of the Four karst filling

Abstract Although the general tectonic history of the Ile Cremieu area (southern Jura) is known, establishing the chronology of events that have influenced the tectonic evolution seems to be much more difficult. A newly discovered layered karst filling in the Bajocian limestone, in the town of Four (Isere), is a synsedimentary evidence of a Tertiary tectonic activity. Actually, only the lower part of the filling has been folded by the movement of the fault in which the karstic network was made. Fossil mammals date the last movement on this fault plane, between 13.0 and 13.4xa0Ma. At a larger scale, the last activity of this fault could be correlated with a change in the paleo-stress field generated by the Alpine orogen, dating with precision an Alpine tectonic event.