Description and Classification

Wulianbaatar was a small mammal, probably about the size of a modern squirrel or rat. Like other multituberculates, it had a unique type of teeth. Multituberculates are an extinct group of early mammals. They are often called the “rodents of the Mesozoic” because many were small, numerous, and had teeth good for gnawing and grinding, similar to rodents today, though they are not directly related to modern rodents.

The most important feature of multituberculates, including Wulianbaatar, is their molar teeth, which had many small bumps, or “tubercles,” arranged in rows. These teeth were excellent for grinding up food. They also typically had a pair of large, blade-like teeth in their lower jaw, which were the last premolars, possibly used for slicing or cracking tough seeds or shells. Wulianbaatar is classified within the order Multituberculata. This was a very successful lineage of mammals that first appeared in the Jurassic period and survived even past the extinction of the non-avian dinosaurs, living well into the Eocene epoch. It is considered part of a group of advanced Asian multituberculates, likely related to other small mammals such as Kryptobaatar and Djadochtatherium, which lived in similar ancient environments in Asia.

Distinguishing Features

Wulianbaatar can be recognized by several key characteristics, mostly related to its teeth and skull, which are typical of many multituberculates:

• It was a small, agile mammal species and, like other mammals, was likely covered in fur and warm-blooded.
• Its molar teeth had multiple cusps (bumps) arranged in parallel rows, specifically designed for efficient grinding of food materials.
• It possessed a distinctive, large, blade-like lower premolar tooth on each side of the jaw, used for cutting, piercing, or cracking.
• The overall skull structure indicates adaptations for strong chewing muscles, allowing it to process tough food items.

These features helped Wulianbaatar to find and eat food in its specific environment.

Paleoenvironment and Diet

Wulianbaatar lived in an area represented by the rock layers of the Wulansuhai Formation in Inner Mongolia. During the Late Cretaceous period, this region was likely a semi-arid environment. This means it was quite dry, possibly with sand dunes, scattered vegetation like bushes and shrubs, and rivers or streams that might not have flowed all year round. The climate might have been similar to parts of the Gobi Desert today.

In this challenging habitat, Wulianbaatar shared its home with a variety of dinosaurs. These included plant-eating dinosaurs such as ankylosaurs (armored dinosaurs) and protoceratopsids (relatives of Triceratops, like Protoceratops), as well as meat-eating dinosaurs such as oviraptorosaurs (dinosaurs that looked somewhat like birds) and possibly small tyrannosauroids. Lizards, turtles, and other small vertebrates also lived there. Based on its specialized teeth, scientists believe Wulianbaatar was probably an omnivore, eating both plants and small animals, or an herbivore focusing on plants. It likely ate seeds, nuts, tough fruits, and perhaps insects. Its sharp, blade-like premolars would have been very useful for cracking open hard seeds or the tough outer shells of insects.

Significance and Ongoing Research

The discovery of Wulianbaatar is important because it adds to our knowledge of multituberculate mammals, especially those that lived in Asia during the Late Cretaceous period. Fossils like those of Wulianbaatar help scientists understand how diverse these early mammals were and how they adapted to live in ecosystems that were largely dominated by dinosaurs. Studying these small mammals gives us clues about how mammals survived and eventually thrived after the dinosaurs went extinct.

Ongoing research on Wulianbaatar and its relatives focuses on several areas. Paleontologists continue to study new fossil finds, when available, to learn more about its detailed anatomy and how it might have moved or behaved. They also work to understand its exact place in the multituberculate family tree by comparing its features to other known species from around the world. Reconstructing its diet and lifestyle helps scientists paint a clearer picture of the entire food web and the ancient environment of the Wulansuhai Formation millions of years ago. Each discovery helps us learn more about the complex world of the Cretaceous period and the fascinating early evolution of mammals, our distant ancestors.