Multituberculata

Multituberculata, often called multituberculates, were a special group of extinct mammals. They had teeth with many tiny bumps, called “tubercles.” These animals lived over 130 million years ago, first appearing in the Middle Jurassic period. They were most common during the Late Cretaceous and Paleocene. Sadly, they slowly disappeared and were gone by the late Eocene.

With more than 200 known species, multituberculates were the most varied group of mammals when dinosaurs lived. They came in many sizes, from as small as a mouse to as large as a beaver. Some lived underground in burrows, others climbed trees like squirrels, and a few hopped around like small rabbits.

Scientists think multituberculates are not part of the two main groups of living mammals—placentals and marsupials. Instead, they seem closer to placentals than to monotremes. They may be related to groups like Euharamiyida and Gondwanatheria, all part of a bigger group called Allotheria. These ancient mammals help us learn about life on Earth long ago.

Description

The multituberculates looked like small rodents, with teeth that had many tiny bumps called tubercles. Unlike rodents, whose teeth grow forever, multituberculates' teeth were replaced in a pattern seen in other mammals. They had a special large tooth called a plagiaulacoid, which most other mammals do not have.

Multituberculates chewed food differently from rodents. Their jaws moved front to back, not side to side, giving them a unique way to grind food. Scientists think they may have had long pregnancies, like some modern mammals, and they gave birth to very small babies. Some multituberculates had teeth that grew long, coming out above the gumline. Recent studies show that these animals had fairly complex brains.

Evolution

Multituberculates first appeared in the fossil record during the Jurassic period and lived for over one hundred million years. They were around longer than any other early group of mammals. The earliest multituberculates lived during the Middle Jurassic, about 166-168 million years ago, in places like England and Russia. During the Late Jurassic and Early Cretaceous, these small mammals were common in Europe, Asia, and North America.

Multituberculates had many different shapes and sizes. Some were like squirrels and could climb trees. Others were larger and lived on the ground. Their special teeth, with a long, blade-like premolar, helped them eat seeds, nuts, insects, and fruits. One well-known multituberculate was Ptilodus, which lived in North America and had feet similar to modern squirrels.

Classification

Multituberculata is grouped within Allotheria along with Euharamiyida, a group of mammals from the Middle Jurassic to Early Cretaceous of Asia and possibly Europe.

Gondwanatheria is a group of allotherians that lived during the Late Cretaceous in South America, India, Madagascar, and possibly Africa, continuing into the Paleogene in South America and Antarctica.

In a 2001 study, researchers Kielan-Jaworowska and Hurum identified two main suborders of multituberculates: "Plagiaulacida" and Cimolodonta, except for the genus Arginbaatar.

"Plagiaulacida" is an early group and includes basic multituberculates from the Middle Jurassic to the mid-Cretaceous.

Cimolodonta is a group with more advanced multituberculates from the lower Cretaceous to the Eocene. This group has several families, such as Djadochtatherioidea, Taeniolabidoidea, Ptilodontoidea, and Cimolomyidae. More research is needed to understand their exact relationships.

Paleoecology

Multituberculates were some of the first mammals to live in groups and build burrows together. One species, Filikomys, lived in North America during the Late Cretaceous and built nests that lasted for many generations.

Multituberculates lived for over 130 million years but eventually went extinct. They were most diverse during the early Palaeocene but slowly disappeared by the early Oligocene. Scientists have many ideas about why they died out. Some think it was because rodents became better at eating tough seeds. Others suggest that changes in climate and plants played a role. In Asia, multituberculates lived alongside rodents and did not go extinct, showing that competition might not have been the only reason they disappeared.