It’s fun to go to a museum to view the mounted dinosaur skeletons. In the Royal Tyrrell Museum in Drumheller, Alberta, the poses suggest tension. There are running dinosaurs, fighting dinosaurs, carnivorous dinosaurs about to kill herbivore victims, and others caught in the act of raiding dinosaur nests. The displays are actually stories without words. At a glance they communicate current scientific interpretations about dinosaur lifestyles. But these are not the really dramatic displays. It is the dinosaur skeletons still entombed in rock, which should rivet our interest. These artifacts cry out with information.
Two specimens particularly claim our attention. They are so different and yet so much the same. Both were found in Dinosaur Provincial Park. The first, discovered during World War I, turned out to be an almost complete skeleton. Struthiomimus, the largest of bird-mimic dinosaurs, was more than 3 m long. The body was comparatively small however since these animals were proportioned much like an ostrich. These dinosaurs ran on two muscular legs and their heads appear to have been amazingly bird-like in shape. They may have eaten plants or they may have feasted on eggs.
The specimen discovered in 1917 by Henry Fairfield Osborn, was carried to New York City and is on display there. A cast is on view in the Royal Tyrrell Museum. This nearly complete skeleton is preserved in a most striking pose. Apparently numerous herbivorous duckbill dinosaurs, carnivorous dinosaurs and bird-mimics are entombed in similar postures. Pioneer dinosaur explorer Loris Russell described such victims: “… lying on one side, with the tail stretched out, the hind limbs flexed, the front limbs extended, and the neck and head bent back over the shoulders.” (Rotunda 19 #2 p. 29). It is as if he was looking at this Struthiomimus when he wrote those words.
The other specimen was discovered only in 1991. It is the articulated skeleton of a large carnivore called Albertosaurus. These fierce animals that ran on two legs, were much like tyrannosaurs, only smaller. Nevertheless some were as long as 8 m. The specimen on view measures about 5 m long. This is the best preserved and most nearly complete specimen of the 19 skeletons of this species which have been collected in Alberta. While a few bones are missing, it is interesting that the entire tail is present including the last vertebra which is only 5 mm long. Even more interesting is the dramatic pose. Both neck and tail are arched over the pelvis. The head even faces backward and the mouth is gaping open. It takes little reflection to imagine a scream coming from this victim. It is impossible not to ask the question: What happened to these victims?
A number of explanations for these strange dinosaur postures have been proposed. Loris Russell, from his ample experience in the field, has one explanation: “There seem to be no signs of a struggle; the dinosaurs appear to have quietly collapsed on their sides in the mud.” (Rotunda 19 #2 p. 29) Few people agree with this interpretation. Another one is suggested by the sign which accompanies the Struthiomimus display in the museum. It attributes the pose to “drying out of ligaments and muscles along the backbone after death. As they dry they pull the head back and the tail forward.” This explanation, although often proposed for such poses, is a surprising one in the Alberta context. In short, it does not fit the other evidence.
From ample preserved plant material in the same sediments in Dinosaur Provincial Park, scientists have developed a picture of the landscape during the time of the dinosaurs. The kinds of plants that grew there give us clues as to what the climate was like at the time. Both the vegetation and the climate were very different from that characteristic of Alberta today. The lush semi-tropical flora featured such trees as dawn redwood, baldcypress, ginkgo, relatives of Norfolk Island Pine, areca palm, and tree ferns. Such plants need a warm and moist climate. A field guide to Dinosaur Provincial Park refers to the “high precipitation-evaporation ratio” and the “absence of reports of any evaporitic paleosol types.” Both these technical phrases in the guide written for petroleum geologists, indicate that there is no hint of drought conditions in the sediments of Dinosaur Provincial Park. Whatever the dinosaurs had to contend with there, drought was not one of their problems.
If drought was not a factor in the remarkable dinosaur postures, what was the cause? The surprising answer is that the alternative is catastrophic flooding. But how could scientists confuse such a dry cause from so wet an alternative? How indeed. Scientists have long been aware that articulated skeletons (those with all the bones arranged in the position as in life) are very remarkable artifacts. The animal carcasses must be buried quickly before decay or scavengers can separate the bones and allow them to be scattered. Some scientists have proposed that drying of carcasses might allow for a delay between death and seasonal floods. Recent terrible droughts in Africa have provided scientists with the opportunity to test this idea.
During 1970 and 1971 a prolonged drought gripped Kenya’s Tsavo East National Park. Thousands of elephants died. Oxford University’s Malcolm Coe undertook the unsavoury job of documenting what happened to the carcasses. Would the drought cause them to be mummified and preserved? Apparently not. Coe found that in a climate like Kenya’s, the bones flaked and cracked within five weeks. Within a year the bones were scattered far and wide. Dr. Coe found moreover that delicate bones from smaller animals disintegrated even more quickly than large bones. Only if bones were quickly and permanently buried in sediments carried by a flooding river, did they have much chance of being preserved. (Discover January 1981 p. 85) The field trip guidebook to Dinosaur Provincial Park (1984 p. 43) said the same thing: “As a general principle, the degree of carcass decomposition and skeletal disarticulation relates strongly to the time elapsed between mortality and burial.” The better the condition of the preserved skeleton, the faster it was deeply buried. In general only raging flood waters are able to deliver such quantities of sediment quickly enough to preserve the bones. Landslides and volcanic eruptions could do it too, but suitable terrain for such events is rare.
Dr. Coe’s studies have discredited drought as a general method of carcass preservation. Palaeontologists are however reluctant to embrace the alternative: catastrophic flooding. The fascinating case of the Coelophysis fossils at Ghost Ranch, New Mexico, springs to mind. Hundreds of articulated skeletons of this agile carnivore have been found in a quarry along with the separated bones of hundreds of other individuals of the same species. This is the final resting place of at least 1000 animals. Adult Coelophysis dinosaurs were about 3 m long but their bodies were streamlined and their bones were delicate and hollow. These animals probably weighed no more than 30 kg.
When one encounters the scene of a disaster such as this, the first reaction is to ask what happened. We find that the bones are unusually well preserved, thus rapid burial is indicated. The fact that animals of all ages are buried here suggests that a single catastrophic event overtook a whole herd. Normally when attrition claims members of a herd, it is the very young and the very old that are vulnerable. It is the very small and the very big bones that we would expect to find. But here every size is represented. Only very unusual catastrophes kill a whole herd. The posture of the articulated skeletons suggests two explanations to the scientists involved: “the long necks and-or tails are commonly strongly recurved over the bodies suggesting desiccation (drying out) of Coelophysis carcasses before burial” (Schwartz and Gillette. 1994. Journal of Paleontology 68 # 5 p. 1124). But the same posture, later on the same page, is said to indicate “The recurved posture of complete skeletons combined with alignment of the remains further suggests the dinosaurs were transported to the quarry site by fluvial (river) currents as carcasses.”
So what killed these dinosaurs? Initially it had been suggested that these animals were the victims of a volcanic holocaust. There is no evidence however to suggest volcanic activity in this vicinity. Others have suggested poisonous drinking water, sticky mud or drought! But none of these explanations accounts for rapid burial in water-borne sediments. The authors admit that mass drowning is a possible explanation. However they dismiss this conclusion with a flimsy excuse: “Mass drowning is also a possible explanation for the death of the dinosaurs …. However, fossil assemblages resulting from mass drowning tend to mirror the recent in that the victims are dominantly herding herbivores.” (Schwartz and Gillette p. 1126) These authors conclude that since only herbivore herds like caribou are known to drown today, so only herbivore herds drowned in the past. The fact is that there are no large carnivore herds today. Thus we have no basis to say what is or what is not a reasonable cause of death. The authors’ choice of drought as an explanation for the Coelophysis calamity is in spite of the evidence for rapid permanent burial in water-borne sediments.
The Coelophysis skeletons were entombed in rock along with countless individual bones and bone fragments. Such massive collections of bones, buried in water-borne sediments, are called bonebeds. These deposits are astonishingly common in western North America. Like the Coelophysis quarry, many contain the remains of thousands of animals. Often these are the remains of entire herds, generally herbivores. The Centrosaurus bone bed in Dinosaur Provincial Park contains bones deposited as thickly as 60 per square meter. Thousands of animals are buried in this deposit which stretches 8 km. The conclusion of the experts is that these horned dinosaurs drowned in raging waters and were left buried by the sediments carried therein. An equally impressive bonebed near Grande Prairie, Alberta contains the remains of a large herd of Pachyrhinosaurus dinosaurs “killed en masse by some calamitous event.” And what might this event have been? “A flash food is the best guess.” (Edmonton Journal July 2, 1989).
Thus sometimes scientists conclude that a flash flood was the event which killed and entombed various dinosaurs. Other authors still prefer drought. But the basis of their conclusions appears to be a desire to keep really big floods out of their explanations. An article on dinosaur bonebeds in Montana includes in the title a prominent reference to drought. The author admits however in his discussion “Mass drowning within a fluvial channel with subsequent concentration of carcasses outside the active channel cannot be completely repudiated….(but) It would require a major flood event to transport intact dinosaur carcasses across a floodplain…” (Raymond Rogers. 1990. Palaios v. 5 pp. 405-406).
Despite the preferences of various scientists, we know that articulated dinosaur skeletons are the result of flood waters raging on a scale unimagined today. The quantity of water and the speed of the currents necessary to carry along enough sediment to permanently bury large dinosaurs is certainly food for thought. Delicate skeletons are even more interesting because they would disintegrate even faster than large specimens. So how about the Struthiomimus skeleton on view in the Royal Tyrrell Museum. The field guide to Dinosaur Provincial Park says “Most of the individual vertebrates which became fossils, irrespective of the degree of disarticulation, died in river water.” (p. 43) Whether the fossils are articulated skeletons or collections of individual bones, this guide written for petroleum geologists, suggests that all these victims drowned. Since Struthiomimus was found in Dinosaur Provincial park, the sign accompanying the bird-mimic display is incorrect to attribute its posture to drought. We know now also how the agonized Albertosaurus died. The stressed postures convey something of the horror of the disaster that overtook these creatures. These fossils convey a powerful message of death in a spectacular flood.
Some might claim that seasonal floods were the agents of disaster. Everyone must admit however that the scale of the flooding was highly unusual, like nothing seen today. During this decade of terrible floods in North America, why not reflect on the scale of the flooding which overtook the dinosaurs.
This article first appeared in Reformed Perspective in June 1997.
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