Abstract
Theridomyids were the most diverse and abundant rodents from the Late Eocene to Late Oligocene in Western Europe. As they lived in an archipelago, almost completely (Late Eocene) or partly (Oligocene) isolated from other continental areas, their evolution remained mainly insular, leading to an increase of evolutionary rates. If theridomyids are most often known from isolated teeth, partial postcranial material remains available. A few subcomplete skeletons of a ricochetal theridomyids (i.e. Issiodoromys) have already been studied, but their locomotor adaptations have unlikely been restricted to leaping habits, especially in the basal members of the group. The numerous isolated postcranial bones collected in the Paleogene Quercy localities and other Western European areas allow us describing for the first time the anatomy of the pivotal bones of the theridomyid locomotor apparatus, in order to approach their specificity and diversity. We also performed Factorial Discriminant Analyses (FDA) to evaluate theridomyid locomotory behaviour and body shape in comparison with extant taxa. Despite the limited number of taxa for which postcranial data are available, at least four different types of locomotion can be characterized: 1- the terrestrial quadrupedal (semi-fossorial?) Suevosciurus, 2- the ricochetal Issiodoromys, 3- the putative arboreal Theridomys bonduelli, 4- the putative cursorial Blainvillimys.