AGE:
Late Cretaceous, Barun Goyot Formation, 75 million years ago.

SIZE:
About the size of a large rat

PRONUNCIATION:
Ka-TOP-sa-lis

CLASSIFICATION:
MULTITUBERCULATA: Taeniolabididae

The mammals, those descendants of the mammal-like reptiles, which thrived in the Permian and Triassic only to disappear in the Jurassic, survived as small animals during the time when dinosaurs were supreme.

One of the most extensive records of mammals of the Mesozoic Era in earth's history (the Age of Reptiles or Dinosaurs) is to be found in the Cretaceous rocks of the Peoples' Republic of Mongolia.

Catopsalis is one of the small mammals known from Mongolia. It had a set of teeth very similar to those of rodents and yet Catopsalis was only distantly related to rats and mice. Catopsalis belonged to a group of mammals now completely extinct that arose about the time the dinosaurs did and persisted until 40 million years ago.

This group, the multituberculates (in reference to the many cusps on their molar teeth), was one of the most diverse mammalian groups that lived alongside (rather, underneath!) the dinosaurs.

When dinosaurs died out, the multituberculates went into a marked decline, while other groups of mammals diversified rapidly. Multituberulates may have been the Cretaceous and early Cainozoic ('Age of Mammals') counterpart of the rodents, which didn't appear until about 50 million years ago. Interchange of animals between North America and eastern Asia occurred frequently in the Late Cretaceous. Presumably they moved along a landbridge in the Bering Straits region.

Catopsalis is just one of the many mammals that crossed this route as did several dinosaurs such as Saurolophus and Corythrosaurus.Catopsalis, a primitive mammal (multituberculate) skeleton and restoration.(From The Fossil Book, courtesy of Doubleday, New York)