Grasslands National Park in southern Saskatchewan is well known for its rolling hills, breathtaking badlands, and inquisitive prairie dogs. One sign instructs visitors to “shoo the prairie dogs away with enthusiasm”. But the park is also one of the best places in the world to understand how this little mammal, and all its furry mammalian relatives, came to replace the dinosaurs.

A panoramic view of the badlands in Grasslands National Park
A view of the badlands in the East Block of Grasslands National Park. In the summer of 2017, a Canadian Museum of Nature-led team made its first foray into this area to scout for promising exposures of fossil-bearing rocks. Image: Danielle Fraser © Canadian Museum of Nature

That’s because the park is rich in fossils that tell us of the dramatic environmental and faunal changes that have occurred since the extinction of the dinosaurs.

This past summer, I led a small team of intrepid female palaeontologists exploring the park as part of my research into the evolution of mammals.

Five researchers posing for a photo in Grasslands National Park
The museum’s 2017 extinct mammals prospecting team, from left to right: Carleton University student Brigid Christison, museum technician Margaret Currie, museum research scientist Danielle Fraser, and University of Calgary student Abigail Hall. Far right is Emily Bamforth, a curatorial assistant at the T. Rex Discovery Centre in East End, Saskatchewan. Emily kindly provided an overview of the stratigraphy and topography of the East Block at the start of the fieldwork. Image: Joshua Erikson, © Joshua Erikson

Wherever we went in the East Block (the park is divided into separate eastern and western chunks), it was difficult to miss the coal seam that marks the Cretaceous-Paleogene Boundary (KPg), the end of the dinosaurs and the beginning of the age of mammals, about 66 million years old. At times we literally tripped over the moment in time that dinosaurs went extinct.

A close-up view of the coal seam in the earth
A small exposure of the coal seam that marks the Cretaceous-Paleogene Boundary (KPg) and the extinction of the dinosaurs. Image: Danielle Fraser, © Canadian Museum of Nature

The rocks at the KPg boundary record an environment much more tropical than modern Saskatchewan and a mammal fauna very different from today.

On the very top of the hills, we uncovered the first 20 million-year-old fossil sites ever found in the park. These much younger rocks record an environment that would have looked more familiar to us today, with a mix of forest and grassland. It was an environment populated by a variety of mammals with hooves, including three-toed horses, rhinoceroses (yes, rhinos!), and relatives of the living pronghorn.

A hill in Grasslands National Park
The museum team prospects for fossils on a hill of post- Cretaceous-Paleogene Boundary (KPg) rocks. Next summer, museum researcher Danielle Fraser will continue searching as part of a multi-year project to recover and describe the fossil mammals of Grasslands National Park. Image: Danielle Fraser, © Canadian Museum of Nature.

On future expeditions to Grasslands National Park we will continue to search the rocks immediately after the KPg for fossils of early primate-like mammals (Plesiadapiformes) and other extinct mammal lineages.

Plesiadapis model and tooth of a three-toed fossil horse
Left: A model of the extinct early mammal, Plesiadapis. About the size of a squirrel, this little mammal belongs to an extinct group that’s perhaps ancestral to primates, including humans. Image: M. De Stefano, © MUSE-Museo delle Scienze (CC BY-SA 3.0). 
Right: Covered in lichen, the tooth of a three-toed fossil horse. This fossil likely represents a member of the genus Archaeohippus, a small horse, about the weight of a medium-sized dog, that lived about 20 million years ago. Field number: GNP2017-WM2-18-1. Image: Brigid Christison, © Canadian Museum of Nature.

In comparing such specimens with fossils from the younger overlying layers we hope to paint a picture of how mammals responded to the extinction of the dinosaurs and to the extreme environmental changes that have occurred over the past 66 million years.

And how this all combined to produce the curious little prairie dogs.