Discovering ‘The Great Reptiles’ of the Past
WHEN you stand on the edge of the Red Deer River valley, just south of the town of Drumheller in Alberta, Canada, you stand on the edge of two different worlds. At eye level, in every direction, are the endless wheat fields of the Alberta prairies. But looking down the cliffs into the dry and barren valley, visitors can imagine another world far removed from their own—the world of the dinosaurs.
In this valley, with its steep canyons of multicolored sedimentary rock layers, hundreds of dinosaur bones have been unearthed. Some people in this area call the barren canyon “the badlands.” But visitors, young and old alike, are filled with astonishment as they view the fossil legacy of some of the most amazing animals that ever lived on earth.
Before 1824, dinosaurs were unknown to man. In that year the bones of several kinds of fossilized reptiles were unearthed in England. British paleontologist Richard Owen called these animals Dinosauria, from the two Greek words deinos and sauros, meaning “terrible lizard.” The name remains in common use to this day, although while dinosaurs are reptiles, they are not lizards.
Since 1824, dinosaur fossils have been found on every continent. The fossil record, left in layers of sedimentary, or water-laid, rock, indicates that there was an extraordinary abundance and variety of dinosaur types at a time in earth’s history called the Age of Dinosaurs. Some made their home on land, while others lived in swamps. Some perhaps even lived in water, much like the present-day hippopotamus.
Large quantities of dinosaur remains—including such nonskeletal evidence as tracks—have been unearthed in the Great Central Plain of North America. The prairies of central Alberta have yielded many dinosaur remains, including nearly 500 complete skeletons. In the 1920’s, expeditions discovered dinosaur bones in the Gobi Desert of central Asia. In the 1940’s a Soviet expedition in Mongolia discovered a dinosaur skeleton some 40 feet [12 m] in length.
In 1986 Argentine scientists discovered the fossils of a plant-eating dinosaur in Antarctica. Until then, Antarctica had been the only major land area where dinosaur fossils had not been found. Just before that, an American researcher found dinosaur bones on the North Slope of Alaska. Throughout the last hundred years, deposits of dinosaur bones have been uncovered in so many places that it has become apparent that dinosaurs were widespread in the remote past.
When Did They Live?
Dinosaurs played a dominant role in life on earth during their age. But then they came to an end. The rock layers containing human fossils consistently occur above those layers containing dinosaur fossils. Because of this, scientists generally conclude that humans came on the earthly scene later.
In this regard the book Palaeontology, by James Scott, states: “Even the earliest species of Homo sapiens (man) lived long after the disappearance of the dinosaurs . . . After tilting (through earth movement) has been allowed for, rocks containing fossil men consistently occur above those preserving the bones of the great dinosaur reptiles and it follows that the latter belong to an earlier age than the human remains.”
In the Red Deer River valley, there is a layer of sedimentary rock that contains dinosaur bones. Just above this, there is a purplish-brown layer that follows the contour of the hillside. On top of the purplish-brown layer is a layer of brownish siltstone containing fossils of subtropical ferns, indicating a hot climate. Above this, there are several layers of coal. Farther up the hillside are coarser-grained layers of earth. There are no dinosaur bones in any of the higher layers.
The book A Vanished World: The Dinosaurs of Western Canada states that “all of the 11 major kinds of dinosaurs . . . ceased to exist in the western interior at about the same time.” This, and the fact that human bones have not been found with dinosaur bones, is why most scientists conclude that the Age of Dinosaurs ended before humans came on the scene.
However, it should be noted that there are some who say that dinosaur bones and human bones are not found together because dinosaurs did not live in areas of human habitation. Such differing views demonstrate that the fossil record does not yield its secrets so easily and that no one on earth today really knows all the answers.
Scientists have concluded that east of the North American Rocky Mountains, a great shallow sea once existed. This sea was hundreds of miles wide, extending from the present Arctic Ocean to Mexico. Along the flat shoreline were lush, marshy forests. Fossils suggest that many types of dinosaurs flourished in this ecological setting. The edmontosaurus, a duck-billed dinosaur about 30 feet [9 m] long, apparently browsed in herds in cow fashion through the swamp. Well-preserved three-toed footprints and the fossilized contents of the stomach led paleontologists to this conclusion.
Other evidence suggests that some dinosaurs displayed social habits. They likely herded together, perhaps in groups of hundreds or more. Discovery of successive layers of nests and eggs in the same place indicates that some dinosaurs returned to the same nesting sites year after year. Skeletal remains of infant dinosaurs near the nests, states Scientific American, ‘strongly suggest sibling social behavior and also imply the possibility of parental attendance on the young after their hatching.’
The fossil evidence thus demonstrates that there were vast numbers and varieties of dinosaurs. But just what did they look like? Were they all fearsome, gigantic monsters—“terrible lizards”? Why did they seem to disappear so suddenly?
[Picture Credit Line on page 3]
Smithsonian Institution, Washington, D.C.: Photo Number 43494