A Chinese triconodont mammal and mosaic evolution of the mammalian skeleton

Here we describe a new triconodont mammal from the Late Jurassic/Early Cret aceous period of Liaoning, China. This new mammal is represented by the bes t-preserved skeleton known so far for triconodonts which form one of the ea rliest Mesozoic mammalian groups with high diversity. The postcranial skele ton of this new triconodont shows a mosaic of characters, including a primi tive pelvic girdle and hindlimb but a very derived pectoral girdle that is closely comparable to those of derived therians. Given the basal position o f this taxon in mammalian phylogeny, its derived pectoral girdle indicates that homoplasies (similarities resulting from independent evolution among u nrelated lineages) are as common in the postcranial skeleton as they are in the skull and dentition in the evolution of Mesozoic mammals. Limb structu res of the new triconodont indicate that it was probably a ground-dwelling animal.