He started it: 'Jurassic rat' from 160million years ago that spawned rodent dynasty is unearthed in China. Multituberculates first appeared in the Late Jurassic, and went extinct in the early Oligocene, with the appearance of true rodents. Over 200 species are known, some as small as the tiniest of mice, the largest the size of beavers. And other orders such as marsupials and monotremes, although under pressure, have managed to hold on in isolated areas such as Australia and even in the Americas, in the case of opossums where competition from “our” mammal oder would have been more intense. Competition from rodents has been suggested, yet what do rodents have that multituberculates lack? Multituberculates filled a … Two questions – why did they die out? Multituberculate, any member of an extinct group of small, superficially rodentlike mammals that existed from about 178 million to 50 million years ago (that is, from the middle of the Jurassic Period until the early Eocene Epoch). Vermin problem? While most mammals — along with birds and other dinosaurs and most other types of life — were wiped out during the K-T event (the extinction of the dinosaurs 65 million years ago), a large proportion of the mammals that show up in the fossil record after the extinction are multituberculates. During most of this span, they were the most common mammals.