Xianshou linglong (Wang, Meng, Bi, Guan and Sheng, 2014; Late Jurassic, the size of a chimpmunk) is a pre-multituberculate with a large traditional 3rd lower premolar and a multicusped double rooted incisor. The jaw joint was loose.
Rugosodon eurasiaticus (Yuan et al. 2013, Late Jurassic, the size of a chimpmunk) is the oldest multituberculate and it is represented by a complete skeleton. Teeth and ankle evidence indicate it was an omnivore and arboreal.
Meng Q-J, Grossnickle DM, Liu D, Zhang Y-G, Neander AI, Ji Q and Luo Z-X 2017. New gliding mammaliaforms from the Jurassic. Nature (advance online publication)
doi:10.1038/nature23476
Yuan CX, Ji Q, Meng QJ, Tabrum AR, Luo ZX 2013. Earliest evolution of multituberculate mammals revealed by a new Jurassic fossil". Science 341 (6147): 779–783. doi:10.1126/science.1237970.