Multituberculata

The Multituberculata (multituberculates) are a major branch of mammals that survived for a long period of time but eventually became completely extinct at the end of the Paleogene period.

History

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 160 million years ago, survived the mass extinction in the Cretaceous, and became extinct in the early Oligocene epoch, 35 million years ago.

Geographic distribution

With the possible exception of some poorly preserved South American material, multituberculates are only known from the northern hemisphere. A southern grouping, Gondwanatheria, has in the past been referred to the order, though this placement currently has little support.

In the late Cretaceous multituberculates were widespread and diverse in the northern hemisphere, making up more than half of the mammal species of typical faunas. Although some lineages became extinct during the faunal turnover at the end of the Cretaceous, multituberculates managed very successfully to cross the K/T boundary and reached their peak of diversity during the Paleocene. They were an important component of nearly all Paleocene faunas of Europe and North America, and of some late Paleocene faunas of Asia. Multituberculates also were most diverse in size during the Paleocene, ranging from the size of a very small mouse to that of a beaver.

Biology

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. The multituberculates were also the first mammals to live in trees like the modern squirrel. In the northern hemisphere during the late Cretaceous, more than half of typical land mammalian species were multituberculates.

About 80 genera of Multituberculata are known, including Lambdopsalis, Ptilodus and Meniscoessus.

Groups within Multituberculata

In their 2001 study, Kielan-Jaworowska and Hurum found that most multituberculates could be referred to two suborders: Plagiaulacida and Cimolodonta. The exception is the genus Arginbaatar, which shares characteristics with both groups.

"Plagiaulacida" is paraphyletic; it is an informal suborder which does not satisfy the cladistic criterion of consisting of an ancestor and all of its descendants. Its members are the more basal Multituberculata. Chronologically, they ranged from perhaps the middle Jurassic (unnamed material), until the lower Cretaceous. This group is further subdivided into three informal groupings: the Allodontid line, the Paulchoffatiid line, and the Plagiaulacid line.

Cimolodonta is apparently a natural (monophyletic) suborder. This includes the more derived Multituberculata, which have been identified from the lower Cretaceous to the Eocene. Recognized are the superfamilies Djadochtatherioidea, Taeniolabidoidea, Ptilodontoidea and the Paracimexomys group.

Additionally, there are the families Cimolomyidae, Boffiidae, Eucosmodontidae, Kogaionidae, Microcosmodontidae and the two genera Uzbekbaatar and Viridomys. More precise placement of these types awaits further discoveries and analysis.

References

Kielan-Jaworowska Z. and Hurum J.H. (2001), "Phylogeny and Systematics of multituberculate mammals". Paleontology 44, p.389-429.
Most of this information has been derived from Multituberculata (Cope 1884)