It started as a bony mystery that confronted paleontologist Philip Currie in the basement of the American Museum of Natural History. His mind raced with questions as he opened one cabinet, then another, filled with fossils of the sophisticated killing machine known as Albertosaurus.
Where precisely on the Red Deer River had famous American fossil hunter Barnum Brown unearthed these specimens, left virtually forgotten in storage in New York City since their discovery in Alberta in 1910?
Why did Brown’s Albertosaurus cache consist mainly of feet? And what new clues about the 70-million-year-old Albertosaurus might linger in that bonebed, waiting to be uncovered? That was 1996.
Today — after successful detective work in the summer of 1997 to relocate the bonebed based on Brown’s sketchy notes and two black-and-white photographs — that bonebed has significantly reshaped the way Currie and other paleontologists think about the Albertosaurus.
Until the rediscovery of Barnum’s finds and their original resting place, the elephant-sized Albertosaurus was pictured as a solo operator. Books or movies typically show the fierce predator — built like a compact Tyrannosaurus — hunting on its own and relying on incredibly powerful jaws and a mouth full of bone-crushing teeth.
But the rediscovery of the bonebed, added to Brown’s original finds, reveals as many as two dozen Albertosaurus living in the same spot, at the same time.
“It’s the first site where we had big meat-eating dinosaurs clustered in a group,” said Currie, a professor in the University of Alberta’s department of biological sciences. “Back in the late 1990s, we had no other sites that were equivalent to it.”
To mark the 100th anniversary of Brown’s original discovery of that enormous cache of Albertosaurus bones, Currie and his colleagues published their findings in the September issue of the Canadian Journal of Earth Sciences. The entire edition is devoted to the discoveries unearthed in that late Cretaceous Albertosaurus bonebed, located north of Drumheller, Alta., in Dry Island Buffalo Jump Provincial Park.
The research pulls together Brown’s century-old fossil finds with discoveries from the 250 people who painstakingly worked the site over the last 14 summers, including one article on a previously unknown freshwater fish and another on plant life from the era.
But what excites Currie most is the concept that Albertosaurus lived and worked in social groups.
He published a paper in 2000 suggesting that possibility based on Brown’s original finds, which included bones from nine different Albertosaurus.
But this latest article marks the first publication of peer-reviewed research based on evidence collected at the bonebed over the entire century.
Not all paleontologists agree that the ferocious carnivores could have lived in groups; some believe they were simply too aggressive.
But Currie supports the theory with confidence because the Albertosaurus bones spread across the half-kilometre site appear to belong to individuals that all died at the same time — or at least within days or weeks of each other.
The cause could have been a major storm or forest fire, he said, based on the large amount of wood debris, including charcoal, found along with the bones.
The wide age range of the dinosaurs on the site also indicate the Albertosaurus were gathering for a purpose beyond mating.
“The oldest animal we had in the Albertosaurus bonebed was 24 years old, and it’s a big one that is about 11 metres long, bigger than most Albertosaurus we’ve ever seen before,” Currie said. “The smallest is a little guy, only about two metres long and ... only two years old.”
The hard rock makes it difficult work to extract the fossils, something that would have been even more challenging with the equipment available in 1910.
“It was very exciting, of course, because the reality was the more individuals we found, the neater it became, the more perplexing it became,” Currie said. “It’s just crazy to think you can have so many carnivores in one place. Especially if you happen to like working on Tyrannosaurs, like I do, it’s like getting your favourite thing in such abundance.”
Coincidentally, the same year that Currie and his colleagues realized they had uncovered a group of Albertosaurus living together, several of them also helped a South American colleague uncover a cache of bones in Argentina of a big meat-eating dinosaur known as Mapusaurus.
That carnivore now also appears to have lived in a group, a finding that helped bolster the idea that Albertosaurus could work together.
“Unless you have a time machine and can actually go back and see what happened, it’s very hard to know,” Currie said. “But we know anywhere from one dozen to two dozen animals died in the same place at the same time.”
The idea makes sense, he said, when you consider how modern carnivores such as lions or wolves operate, working as a pack to secure their meals.
“We know the big plant eaters were moving in herds. The herds numbered hundreds, thousands of animals,” Currie said.
“When you see that happen with modern animals, the result tends to be that the carnivores also start hunting in packs. They have to break up those herds because you have to eat something,” he added.
Author: Sarah O’Donnell | Source: The Montreal Gazette [October 31, 2010]