Multituberculate

The multituberculates were a group of rodent-like mammals which survived for about 166 million years – the longest fossil history of any mammal line.

They were eventually outcompeted by rodents, becoming extinct during the late Eocene.Krause, David W. 1986. Competitive exclusion and taxonomic displacement in the fossil record: the case of rodents and multituberculates in North America. Contributions to Geology (Special Paper 3): 95–117. 

At least 200 species are known, ranging from mouse-sized to beaver-sized. These species occupied many  ecological niches, ranging from burrow-dwelling to squirrel-like tree-dwelling. 

Multituberculates are usually placed outside both the two main groups of living mammals, the Theria (placentals and marsupials), and monotremes. Some cladistic analyses put them closer to Theria than to monotremes.Benton, Michael J. 2004. Vertebrate palaeontology. p. 300Carrano, Matthew T. et al 2006. Amniote paleobiology: perspectives on the evolution of mammals, birds, and reptiles. University of Chicago Press. p358. ISBN 0-226-09478-2

 Biology 
The multituberculates had a head anatomy similar to rodents. They had cheek-teeth separated from the chisel-like front teeth by a wide tooth-less gap (called the diastema). Each cheek-tooth displayed several rows of small cusps (or tubercles, hence the name) which worked against similar rows in the teeth of the jaw. It was an efficient chopping device.

Most small multituberculates would have eaten seeds and nuts, supplemented with insects, worms, and fruit.

The structure of the pelvis in the Multituberculata suggests that they gave birth to tiny helpless young, similar to modern marsupials.Kielan-Jaworowska, Zofia, Richard L. Cifelli, and Zhe-Xi Luo 2005. Mammals from the Age of Dinosaurs: origins, evolution, and structure. p. 299

 References 

Category:Extinct mammals
Category:Fossils