Saskatchewan’s fossil record, extensive and diverse, covers the last 1.8 billion years. During this immense span of time, life evolved from relatively simple organisms such as bacteria and algae to the vast variety of plants, animals and other organisms living today. In the process, various groups, including dinosaurs, huge marine lizards called mosasaurs, and many others evolved and thrived, only to become extinct. Our knowledge of ancient natural history is necessarily incomplete. For an organism’s remains to be fossilized and preserved for later discovery they must be buried quickly by sediments. In other words, fossils normally form only in locations where sediment is being deposited, such on a lake bottom, but not where erosion predominates, such as on the side of a mountain. Also, most fossils are only discovered when they become exposed at the earth’s surface. Most of Saskatchewan is covered by sediments deposited by the glaciers of the last 2 million years; most of the older rocks that preserve the largest part of fossil history are hidden beneath these recent sediments, and are only exposed in river valleys where erosion has cut down into those older sediments. By 68 million years ago the sea began to retreat from southwestern Saskatchewan, and rocks in the area dated to approximately 65 million years preserve the province’s best record of dinosaurs and their contemporaries. Herbivorous dinosaurs include the horned Triceratops, the duck-billed Edmontosaurus and the armoured Ankylosaurus. A variety of carnivorous dinosaurs are known, such as the smaller dromaeosaurs, Troodon, the ostrich-like ornithomimids, and the largest known meat-eater, Tyrannosaurus rex. Although isolated remains of T. rex had been collected for many years, Saskatchewan’s one partial skeleton of this dinosaur, known as “Scotty,” was discovered in the Frenchman River Valley in 1991. Subsequent excavations recovered approximately 65% of the skeleton. The geology and plant fossils at the site suggest a mild climate with forested lowlands that included palms and cypress-like conifers. The rocks of this age preserve a variety of other animals such as garfish, salamanders, lizards, soft-shelled turtles, crocodiles, the crocodile-like champsosaurs, birds, and mammals. Among the mammals, small opossum-like marsupials and the rodent-like multituberculates predominate. Although mammals remained small until after the extinction of the dinosaurs, sites in Saskatchewan may contain ancestral species of some of the mammal groups that dominated later terrestrial ecosystems.
The oldest fossils found in the province come from uranium-bearing beds near Uranium City. These 1.8 billion-year-old fossils are stromatolites, which consist of mounds of calcareous material produced by blue-green algae. These organisms are still with us today, and the modern stromatolites they produce can be found in intertidal flats off Australia and other locations in the southern hemisphere. The southern two-thirds of Saskatchewan are part of a large sedimentary basin that filled during the last 500 million years. For much of this period Saskatchewan was covered by shallow seas, and as a result the fossils that are preserved are the remains of marine organisms. Approximately 65 million years ago the shallow seas retreated from Saskatchewan for the last time, so that the most recent fossils are of terrestrial and freshwater organisms.
Multicellular life forms became plentiful and diverse by about 600 million years ago. Rocks from the earliest portion of this period are deeply buried in Saskatchewan and poorly known, but limestone rocks from the Ordovician Period (450 million years ago) are exposed at the surface in the Amisk Lake area. These rocks preserve inhabitants of the shallow tropical sea that covered Saskatchewan at that time. Both solitary and colonial corals were present, but the latter did not form the huge reefs found elsewhere. Shelled animals included clams, snails, brachiopods and nautiloids. The nautiloids were predators that are distantly related to the modern octopus and squid; they had straight or slightly curved shells, and a head and tentacles that resemble those of the squid. The sedentary sea lilies (crinoids) might be mistaken for plants with their supportive stalk and branch-like “arms”; in fact, these animals are echinoderms, relatives of the starfishes. The limestones also include lines of darker rock that are interpreted as the burrows of marine worms. These Ordovician-aged limestones are quarried in Manitoba and are used as building stones; this “Tyndall Stone” and the fossils it contains can be seen on the exterior of many buildings in Saskatchewan, including the Saskatchewan Legislative Building and the Royal Saskatchewan Museum, both in Regina.
The subsequent Devonian Period was characterized by the continuation of shallow marine conditions. Massive coral reefs developed in the middle Devonian, but by the late Devonian the water had become too saline to support most forms of life; the conditions were ideal, however, for the deposition of Saskatchewan’s potash. The absence of rocks of latest Palaeozoic age (up to 250 million years ago) suggests that the marine seas had by then retreated from this area. The Mesozoic Era (250–65 million years ago) that followed is often called the Age of Dinosaurs because this group evolved early in the era and dominated terrestrial ecosystems until its extinction 65 million years ago. Although the dinosaurs existed for approximately 150 million years, for much of this time Saskatchewan was again covered by shallow continental seas that would not be expected to preserve fossils of terrestrial animals. Saskatchewan’s dinosaurs come from rocks in the southwest portion of the province that are dated at 75–65 million years ago, when the shallow marine seas were finally starting to retreat from the centre of North America.
Rocks from the last 30 million years of the Mesozoic are exposed in various areas of southern Saskatchewan: as a result we have a good record of the faunas of this time period. Rocks that are approximately 90 million years old are exposed in the Pasquia Hills area just west of the Manitoba border. At that time this area was close to the eastern shore of an inland seaway that extended down the middle of North America. One of the most spectacular fossils recovered from this area is the almost complete skeleton of a 7.5-metre-long crocodile known as “Big Bert.” Big Bert came from sediments along the Carrot River near Pasquia Regional Park; it is the best known example of the species Terminonaris robusta, a member of an extinct group of crocodiles. The sediments in the area preserve other marine reptiles, various fishes including sharks and the 4-metre-long Xiphactinus, and a variety of toothed birds.
Beginning approximately 80 million years ago, some terrestrial sediments were deposited in the western portion of the province. 75 million-year-old sediments containing the remains of horned and carnivorous dinosaurs, fish, lizards, and other terrestrial or freshwater animals are exposed near Unity and at Saskatchewan Landing Provincial Park. By 70 million years ago Saskatchewan was again covered by a shallow sea. Fossils of the shelled invertebrate animals that inhabited this sea are quite common. The coiled ammonites and straight-shelled baculites are extinct relatives of the octopus and the pearly nautilus, and a variety of large and small marine clams are also preserved. The most impressive fossils from this sea are the marine reptiles. The plesiosaurs, which tend to resemble most people’s image of the Loch Ness monster, include both long- and short-necked species. A well-preserved skeleton of a short-necked plesiosaur was discovered near the town of Herschel, west of Rosetown, whereas an elasmosaur, a long-necked plesiosaur, was excavated from a site near Ponteix. Recent research on these two skeletons established that both represent plesiosaur species that are new to science. The other common marine reptiles of this time period are the mosasaurs; closely related to lizards, they had long crocodile-like heads, limbs modified into flippers, and long laterally compressed tails. A very large skeleton of a mosasaur called Tylosaurus was excavated from the southern shore of Lake Diefenbaker near Herbert Ferry in the mid-1990s.
An extraterrestrial impact event 65 million years ago marks the end of the dinosaur era. Because this event, and the intervals both immediately before and after that event, are recorded in sediments in southwestern Saskatchewan, this area is one of the best places to study the faunal and floral changes that occurred during this period of Earth’s history. Saskatchewan’s fossil record of the subsequent Tertiary Period (65–2 million years ago) is the best in Canada. Rocks of Palaeocene age (65–55 million years ago) are exposed in various locations across the southernmost portion of the province. The occurrence of coal and plant fossils of horsetails, ginkgo, cypress, and various broadleafed plants indicates a warm, wet environment of lowland forest and cypress swamps. Animal fossils are less common but record the survival by various fish, salamanders, crocodiles, champsosaurs, and turtles of the extinction event that marked the end of the Mesozoic. Mammal fossils document the beginning of the diversification of this group. Although they were diverse, mammals remained small during the age of dinosaurs, but our Palaeocene rocks include fossils of herbivores that were over two metres in length. Early members of modern mammal groups such as primates, carnivores and ungulates are also present. Earlier groups, such as the marsupials and multituberculates, also persisted; a rare skeleton of a multituberculate was discovered in sediments of this age near Estevan.
The next 12–13 million years of earth history do not appear to be preserved in the province, suggesting that this was a time of erosion rather than deposition of sediments. Deposition of sediments began again about 42 million years ago, and much of the next 30 million years is preserved in sediments in southwestern to south-central Saskatchewan. The fossils document the changes to faunas that occurred as the climate became cooler, drier and more seasonal. During this period closed-canopy forests slowly gave way to open woodland savanna and grassland habitats. The earliest stage of this transition is recorded at a 42 million-year-old site southeast of Swift Current. The habitat was probably still dominated by woodlands, but with some grassy areas. By this time early members of modern mammal groups, including rodents, rabbits, bats, horses, and rhinos, are present, together with members of groups such as multitiberculates that are now extinct. Mammal faunas of approximately 35 million years ago are well preserved in the Cypress Hills area northwest of Eastend. Fossil sites in this area tend to include the broken up remains of many animals rather than complete skeletons. The Calf Creek locality contains specimens representing over 70 mammal species, giving us a very detailed picture of the mammal fauna at the time. This fauna includes many rodents, rabbits, three-toed horses, rhinos, saber-toothed cats, early fox-sized dogs, the pig-like entelodonts, and the massive rhino-like horned brontotheres. The site also includes one of the last records of the rodent-like multituberculates. Although skeletons are rare, two partial brontothere skeletons have been discovered, one near the Calf Creek locality, and one near Simmie. The last known chapter of this 30-million-year period is recorded in localities in the Wood Mountain area near Rockglen. The habitat was probably largely grassland, and the mammals include larger three-toed horses, early pronghorns, camels, and rhinos. The fauna also includes extinct relatives of the modern elephants, a group that had recently arrived in North America. Other vertebrates include extremely large land tortoises. The last 12 million years (14–2 milllion years ago) of the Tertiary Period are not preserved in Saskatchewan sediments.
The last 2 million years of Saskatchewan’s geological history are dominated by a series of ice sheets that advanced and retreated across the province, eroding older rocks and depositing new layers of sediment. A site in Wellsch Valley, northeast of Swift Current, preserves fossils from early in the ice age. The fauna is a mix of animals living today (prairie dog, coyote) and others that are now extinct (mammoth, giant ground sloth, shrubox). Other sites, such as several in the Qu’Appelle Valley, are more recent and contain animals characteristic of the later ice age, such as wooly mammoth and giant bison. A partial skeleton of a wooly mammoth was unearthed near Kyle, north of Swift Current in the 1960s. The ice associated with the last glaciation retreated from Saskatchewan between 17,000 and 8,000 years ago. Most of the land forms we see today are the result of that glaciation. Fossils from this last glaciation, such as bison and mammoth, have been found in many locations throughout the province. Fossils are an important component of Saskatchewan’s rich geological history. They are significant clues to the events of the past, and are the only direct evidence we have of the extinct organisms that once lived here. This irreplaceable heritage resource is protected through the Heritage Property Act.
Harold N. Bryant