Plagiaulacida is a group of extinct mammals. Multituberculates were among the most common mammals of the Mesozoic, "the age of the dinosaurs". Plagiaulacids, an informal suborder, are the most basal of this order, and ranged from the Middle Jurassic Period to the Lower Cretaceous Period of the northern hemisphere. Kielan-Jaworowska and Hurum (2001) divides “Plagiaulacida” into three informal lineages, each of which seems to represent a natural group (an ancestor and all its descendants). However, a firmer conclusion must await further evidence.