Cypress Hills Eocene to Miocene Fossils
The CYPRESS HILLS and Swift Current Plateaux of southwestern Saskatchewan preserve Eocene, Oligocene, and Miocene FOSSILS 42 million to 16 million years old, in the Cypress Hills Formation. Faunas of at least 14 different ages are represented there. Most of the VERTEBRATES that have been studied from the area are mammals, but there are also abundant remains of fishes, amphibians, reptiles, and birds. The deposits that yield these fossil faunas are chiefly sands and gravels from ancient braided streams, but also include lacustrine beds.
This rich fossil record gives the most extensive record in Canada of an important series of climate changes, immigrations from Asia (via BERINGIA), and evolutionary events. The earliest known fossils of the Cypress Hills Formation, found southeast of Swift Current, are middle Eocene, about 42 million years old. They show species that appear to have lived in the last vestiges of the ancient forests that had been typical of the Age of Dinosaurs, with some emergence of meadows. In this fauna we see the appearance of several groups (eg, canids, camelids, LAGOMORPHS) that would assume much greater importance in later years, and last appearances of formerly common groups (eg, mesonychids, condylarths).
Two transitional faunas from the Lac Pelletier area south of Swift Current appear to document the change from more archaic to more advanced land mammals, and the emergence by 37 million years ago of more than a third of the families of land mammals that we see today. This profound turnover of the fauna is partly the result of immigration from Asia, and partly due to EVOLUTION in the more immediate area.
The classic Cypress Hills fauna, best preserved at Calf Creek, near Eastend, is a little more than 35 million years old. Seventy-three species of mammals and a diverse assemblage of fishes, amphibians, reptiles, and birds have been identified from this fauna. The land vertebrates appear to have occupied an incipient savanna, certainly not as open as the later prairie environments. This is the Cypress Hills assemblage discovered in 1883 by R.G. McCONNELL of the Geological Survey of Canada, and later studied by E.D. Cope, L.M. Lambe, and L.S. Russell.
The Eocene-Oligocene boundary, at about 34 million years, marks an abrupt cooling of climate but not many extinctions. Brontotheres are the most widely cited group to disappear from the fossil record at this time. One of the Cypress Hills faunas, dating from very late in the Eocene, preserves the latest known remains of multituberculates. This group, related to neither the marsupials nor the placentals, had been the longest-lived group of mammals, first appearing in the Jurassic period and dominating many mammalian faunas of the Age of DINOSAURS.
A series of early and middle Miocene faunas in the Cypress Hills documents the appearance in Western Canada of several open-country groups, including close relatives of the deer family, which immigrated from Asia about 19 million years ago. A more open savanna grassland was the environment that these mammals probably inhabited.
Along with the somewhat later (about 14 million years old) mammal fauna of the Wood Mountain Plateau to the east, and latest Miocene mammals sparsely represented in the Hand Hills Plateau of southeastern Alberta, the Cypress Hills fossils give us a remarkable view of more than 35 million years of earth history in the Canadian Plains. The dates of these fossil assemblages also provide a time frame for the deep erosion of the Canadian Plains and the emergence of much of the modern topography, most of which occurred between about 5 million years ago, and the beginning of the North American ICE AGE more than 2 million years ago.