A Cretaceous eucosmodont multituberculate mammal skeleton has been found in Mongolia with all of the bony elements of the shoulder girdle in place, This specimen demonstrates a different forelimb stance from that recently hypothesized for another Cretaceous eucosmodont. Primitively, it retains a separate ossified interclavicle, as in monotremes and non-mammalian cynodonts. In other respects it shares with therians and their extinct allies key features associated with mobility of the pectoral girdle and shoulder joint during locomotion, and a more parasagittal forelimb posture, This locomotor transformation appears to have evolved just once among the common ancestors of multituberculates and therians, some time before the Late Jurassic.