Variance of molecular datings, evolution of rodents and the phylogenetic affinities between Ctenodactylidae and Hystricognathi

The von Willebrand factor (vWF) gene has been used to understand the origin and timing of Rodentia evolution in the contest of placental phylogeny. vM F exon 28 sequences of 15 rodent families and eight non-rodent eutherian cl ades are analysed with two different molecular dating methods (uniform cloc k on a linearized tree. quarter dating). Three main conclusions are drawn f rom the study of this nuclear exon. First, Ctenodactylidae (gundis) and Hys tricognathi (e.g. porcupines, guinea-pigs, chinchillas) robustly cluster to gether in a newly recognized clade, named 'Ctenohystrica'. The Sciurognathi monophyly is subsequently rejected. Pedetidae (springhares) is an independ ent and early diverging rodent lineage, suggesting a convergent evolution o f the multiserial enamel of rodent incisors. Second, molecular date estimat es are here more influenced by accuracy and choice of the palaeontological temporal references used to calibrate the molecular clock than by either ch aracters analysed (nucleotides versus amino acids) or species sampling. The caviomorph radiation at 31 million years (Myr) and the pig-porpoise split at 63 Myr appear to be reciprocally compatible dates. Third, during the rad iation of Rodentia, at least three lineages (Gliridae, Sciuroidea and Cteno hystrica) emerged close to the Cretaceous-Tertiary boundary, and their comm on ancestor separated from other placental orders ill the Late Cretaceous.