In 1978 a remarkable discovery was made in western Montana -- the fossilized remains of 15 baby dinosaurs. The presence of many eggshell fragments and of very young dinosaurs indicated that the discovery was a nest. Further exploration and excavation of the nest sites uncovered a number of nests in different stratigraphic horizons. This was evidence that these dinosaurs would return here year after year to rebuild their nests and raise their young. Each nest was about 23 feet from the others, the length of an adult. Because it was evident that the mother cared for the young for a long period, they were named Maiasaura (good mother lizard). Scientists have uncovered the remains of an entire herd in the vicinity of the nesting site; all had died simultaneously, 80 million years ago!
Under the direction of John Horner of the Museum of the Rockies in Bozeman, Mont., seasonal work on the area was continuous during the 1980s. This resulted in uncovering a massive bed of maiasaur bones, with an estimated concentration of up to 30 million fossil fragments covering an area 1.25 miles wide and one fourth of a mile long. All of the bones, without exception, were the remains of a single herd of Maiasaura, conservatively estimated at no fewer than 10,000 dinosaurs of that genus.What could such a deposit represent? The clue was in the layer of volcanic ash that rested just above the layer of bones. Readers may recall that the eruption of Mount St. Helens in 1980 produced widespread ash fall devastation, and volcanoes such as that were run-of-the-mill in the Rockies of Maiasaura's time. The entire herd had been killed by the gases, smoke and ash of a huge eruption. Since there was no evidence of scavengers or predators gnawing on the bones, it doubtless also killed everything else around. One can easily imagine a feeding carpet of dinosaurs aroused from their meal as the volcano exploded and staring in confused disbelief as an enormous choking black cloud of ash swept over them. In a few seconds all were at peace. There remained only a huge killing field strewn with the corpses of 10,000 dinosaurs under a soft cover of volcanic ash. Soon the stench of rotting corpses would have been overpowering. Until ever-present insects cleaned the remains, it must have been one heck of a mess.
Perhaps it is difficult to imagine so great a herd of maiasaurs surviving on just sedges and berry bushes that were the common vegetation of that time. But compared with the bison in the early 19th century that numbered 60 million, this was a bonanza buffet. The buffalo ate only grass. Consider also the demise of the maiasaur herd, a mere sampling compared to the fate of a herd of over 100,000 bison that also lived in Montana but 80 million years later.
The American bison (incorrectly called buffalo) measures 60 to 70 inches at the withers and weighs almost a ton. It is a powerful beast, and the slightest movement of its shoulder muscles reveals a fantastic potential energy that defies comparison with that of any other living creature. So vast were the bison herds that no one imagined they could ever become extinct. Perhaps even nature thought so.
In February 1858 Montana was experiencing an unusually harsh winter that seemed to have reached a climax. A blinding blizzard had been raging for days. The migrating herd of bison knew instinctively that they must keep moving, and move they did. None dared lie down to rest. The vanguard of the herd perceived nothing but a whirling, swirling mass of snow. The howling of the wind was continuous and deafening, and visibility varied from a few feet to a few yards. With the entire landscape blotted out and blended into the white opaque air, the bison headed blindly against the storm and swirling wind. They stayed very close together, and each individual could see only the hindlegs and rumps of the bison in front of it. There was no warning to the front line bison, no variation in color of the snow nor furious movement of the snow-flecked air to alert them to any change in terrain. Even had they been aware of the precipice before them, the front line could not call a halt because of the formidable pressure of thousands of animal engines behind.
Like a carpet shoved over a ledge, the entire herd rolled over the precipice. Nothing could prevent this absolute catastrophe. The wind howled so furiously that the animals couldn't possibly hear the noise of those before them tumbling one over the other from a height of more than 150 feet. They all, 100,000 of them, without a single exception, walked off the cliff to eternity. The vast assemblage of their carcasses spread over hundreds of acres. Eventually it became a boneyard that seemed awesome even to seasoned men of the mountains.
In the days when bison herds roamed the west, the loss of one hundred thousand bison at one stroke was of little significance. They had no real enemies except wolves, American Indians and the elements. One herd might disappear, but a thousand other herds survived. The bison lived on through all seasons, overcoming all difficulties, surviving for centuries. It was as though the American bison was immortal.
Then one fine fall day the white hunter arrived . . .
Phil and Nancy Seff are the authors of several science books, including "Our Fascinating Earth." Their column runs occasionally in the Deseret News's Family Section.