The Multituberculata are the only major branch of mammals to have become completely extinct, with no living descendants. They lived for over 100 million years, and are often considered the most successful mammals in natural history. Rodent-like, they first appeared in the Middle Jurassic, and became extinct in the early Oligocene. The structure of the pelvis in the Multituberculata suggests that they gave birth to tiny helpless young, similar to modern marsupials. They are named for their molar teeth, which had many cusps (tubercles) arranged in rows, hence "multituberculates". They also had a single pair of lower incisors and no canines, reminiscent of modern rodents.