UCM 60031 - Therian Mammal Tooth, Lance Formation, Wyoming
This tiny mammal tooth from the 65 million year old Lance Formation of Wyoming is a typical microfossil from this formation, just the right size for a harvester ant to carry. It came from a small therian mammal, the large group that contains marsupials and placental mammals--almost all modern mammals.
The Lance Formation has produced many important fossils, ranging from tiny microfossils like those collected by harvester ants to fully articulated dinosaur skeletons. It was deposited by streams on a coastal plain stretching along the shallow interior sea of the Western Interior Seaway, which cut North America in half. Dinosaurs, reptiles, fish, amphibians, birds, and small mammals lived in a wet subtropical climate very different from today's dry seasonal climate.
Learn more about the Lance Formation with Passport-In-Time Microvertebrate Fossil Project at the University of Wyoming Geological Museum: Late Cretaceous Paleontological Resources in the Public Eye.