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The Big Splash

The Big Splash


Have you heard the sad story of the dinosaurs that succumbed to a watery catastrophe? Most young people in our province have heard the story of the Centrosaurus herd in Dinosaur Provincial Park. No doubt it would take quite some force to sweep huge, four-footed horned dinosaurs off their feet. The Centrosaurus dinosaurs of Alberta were only moderately large compared to some other horned designs such as Triceratops. Centrosaurus, for their part, were about 5 m (16 ft) long and perhaps 2.5 m (8 ft) tall. But they were certainly chunky and heavy.

Nevertheless something terrible happened to this herd consisting of thousands of animals. Not only were there vigorous adults, but also juveniles (not quite mature) and even elderly, less agile animals. We know that something terrible happened to them all because the bones of thousands of their carcasses ended up smashed together, buried almost up to the present day. (The bone bed was discovered in 1978). This fact, that the bones were smashed together and buried by sediments carried along in raging torrents of water, causes one to wonder about the nature of the flood that overtook these hapless dinosaurs. The interesting thing is that similar tragic events overtook other even larger horned dinosaurs in western North America.

There is no doubt that Pachyrhinosaurus had stranger looking faces than Centrosaurus, or even Triceratops. While not quite as big as the famous three-horned dinosaur, Pachyrhinos were nevertheless pretty impressive. They were about 7 m (23 ft) long and 3 m (10 ft) tall. Typically their skulls, with associated neck frill, might be as long as 1.8 m (6 ft). Indeed the term “ceratopsian” means “horn face.” Not only were these skulls massive, but the bone swept out to the side and up behind to form an elaborate and decorated frill. Pachyrhinos also boasted horns (like those on Viking helmets) and a weird bump on their snouts which may have supported a rhinoceros type projection.

While Triceratops at 9 m, were the longest and heaviest of the group, Pachyrhinos, for their part, may have reached a not insubstantial 8000 kg or 17,500 lbs. These were big heavy brutes — not easily pushed around, one might imagine. Nevertheless there are some spectacular pachyrhino bone beds. A small bed had been found near Lethbridge in the 1970s. Its significance was mainly to establish a “southern” edge to the range of these creatures. Then in 1974 an incredibly rich Pachyrhino bone bed was found 45 km southwest of Grande Prairie in northern Alberta. As with the Centrosaurus event, a large herd appears to have been overtaken by a flash flood. The age range of the victims was even broader than in dinosaur Provincial Park. Not only were there full-grown adults and juveniles, but also very young animals.

The broad spectrum of victims ranging from very small to very large, indicates that this was a herd doing the normal things grazing animals do — rather than a collection of victims which died over a long period of time from old age and predation. In the latter case only the bones of the very old and the very young would be present. In that case the bones would have collected over a lengthy period. Apparently in the case of the Pachyrhinos however, the victims met sudden death when fast moving water engulfed them in enough sand and gravel to bury their bones permanently. Thus buried, they eventually became fossils.

The scope of the flood that overcame the Pachyrhinos of Grand Prairie pales however in comparison with the bed of their bones on Alaska’s North Slope. The quarry with Pachyrhino bones was actually found in 1994. This desolate and cold part of the world is extremely difficult to access however. As a result, active digging did not take place until the summer of 2002. It was then that the palaeontologists found eight skeletons of vigorous adults in an area not quite fifty feet square. When you consider that these animals were each over twenty feet long, that is a lot of bones in that area! The scientists suspect that a huge bed of Pachyrhino bones lies at this site. Their preliminary conclusion is that these animals died in a catastrophic event such as a flood.

The Pachyrhino bone bed becomes all the more interesting however when we realize that this is part of the Colville River bone bed on Alaska’s North Slope. The entire bone bed extends 200 km along the river’s left bank. The first dinosaur bones in the area were discovered in 1967 in the Liscomb bed. It was not until 1985 however that anyone realized that the bones were from dinosaurs rather than bison. Some of the bones were unfossilized, which caused scientists to think they were of relatively recent origin and it never occurred to them that dinosaur bones could last to the present in an unfossilized state. Of course if the dinosaurs died only thousands of years ago, rather than millions, this would be more readily understood.

Thus the Pachyrhinos succumbed to raging flood waters. In this connection, some scientists talk about the case of 10,000 caribou that drowned in a flooded river in northern Quebec in 1985. Apparently the whole herd panicked and animals in the rear of the column were the ones which pushed the leaders into the dangerously rising torrent. Thus the flood did not need to be too extensive. Caribou are however much less sturdy on their feet than Pachyrhinos would have been. Also none of these caribou bones will be fossilized because they were not deeply buried in water borne muck. The scale of the watery disaster that overtook the Pachyrhinos, on the other hand, was such that it not only drowned these animals, but it also engulfed their carcasses in enough sediment to permanently bury these large animals. How many floods have we seen recently that could do that? Don’t forget that the Colville River bone bed is 200 km long and includes the remains not only of Pachyrhinos, but also large duckbill dinosaurs including Edmontosaurus, carnivorous dinosaurs, more dainty Troodon relatives and various tiny rodent-like creatures. Since small animals decay much faster, these require even faster permanent burial for preservation than do large animals. That was some flood!

Margaret Helder
April 2003

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