Introduction to Multituberculates

The “Lost Tribe” of Mammals

Multituberculates are the only major branch ofmammals to have become completely extinct, and have no living descendants. Although not known to many people, they have a 100 million-year fossil history,the longest of any mammalian lineage. These rodent-like mammals were distributed throughout the world, but seem to have eventually been outcompeted by truerodents.

Meniscoessus robustus. Photo by Anne Weil, © University of California Museum of Paleontology.

Multituberculates first appeared in the LateJurassic, and went extinct in the earlyOligocene, 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. Some, such asLambdopsalis from China, lived in burrows like prairie dogs, while others, such as the North AmericanPtilodus, climbed trees as squirrels do today. The narrow shape of their pelvis suggests that, likemarsupials, multituberculates gave birth to tiny, undeveloped pups that were dependent on their mother for a long time before they matured.

Pictured is the reconstructed lower jaw ofMeniscoessus robustus, a squirrel-sized multituberculate from the Upper Cretaceous. This specimen was collected from the Hell Creek Formation of Montana, USA, and is now part of the UCMP collection.

Multituberculates get their name from their teeth, which have many cusps, ortubercles arranged in rows. Although there are some spectacular multituberculate specimens from Mongolia, many of these unique teeth have been found in North America, and UCMP houses a large collection.