"It was the craziest thing I have ever done," Schweitzer said as she described the path that led to her famous discoveries about an eastern Montana dinosaur called B. rex.
Scientists who investigate animals that have been dead for 65 million years sometimes look for clues among the living or at least the more recently deceased, said Montana State University paleontologists who have dug and mapped dinosaur remains all over the world. Jackson and Varricchio are among the MSU scientists who have turned to more modern animals in their quest to understand dinosaurs. Wolff, an MSU graduate student, and Schweitzer, a former MSU graduate student, have done the same.
"The simultaneous drowning of these cows provided a unique opportunity to examine the consequences of mass death within a fluvial system," Varricchio said about some 40 cows that died two years ago after breaking through the ice on the Yellowstone River north of Glendive.
"These cows attempted to cross the frozen edge of the river to drink at a still open stretch," Varricchio explained in a paper he presented to the Society of Vertebrate Paleontology. "The herd broke through the ice, drowned and became entrapped beneath the ice. Here they remained for over a month until the spring melt, when the river, freed of its ice jam, distributed the carcasses downstream."
Varricchio and Jackson realized the potential of the incident that occurred near the end of the 2003-04 winter, so canoed down the Yellowstone River in May 2004 to see if they could find any remains. Successful even during the high waters of paddlefish season, the paleontologists returned two weeks later with students. They made a third trip in September 2004, a fourth in May 2005 and a fifth in September 2005.
"Catastrophic mass drownings have been inferred for a wide variety of vertebrates from titanotheres to hadrosaur dinosaurs, but relatively little modern data exists for comparison," Varricchio said.
Varricchio and Jackson found 33 cows spread over 25 miles when they first canoed the river. Nearly all were intact and severely bloated. Several had unborn calves. The paleontologists found groups of two to five cows as far downstream as 18 miles.
By late September 2004, Varricchio and Jackson found only 17 carcasses, but some of them remained in groups. The most complete carcasses were held together with stiff upper skins, raising the possibility of someday finding dinosaur mummies, Varricchio said. Skulls were relatively scarce, but ribs and shoulder blades were unexpectedly plentiful.
The discovery of groups was important, Varricchio said, because dinosaur bones have been found that way. It supports the theory that mass deaths may have been responsible.
Wolff, Varricchio's graduate student, traveled to Australia last year to present his research on dinosaur wounds and lesions to the Wildlife Disease Association. In his spare time, he observed emus, turtles, lizards, marsupials and cassowaries to see what the primitive animals and birds could teach him about dinosaurs. He also dropped by crocodile farms and zoos, studied crocodiles in the wild and consulted wildlife veterinarians.
"There's a lot of stuff you can read about, but it's a lot more useful to actually see what they do," Wolff said.
Schweitzer, now a paleontologist at North Carolina State University and the North Carolina Museum of Natural Sciences, said she often looks at ostrich and emus, because the primitive birds have more in common with dinosaurs than more advanced birds like robins. To find the ostrich whose bones she compared to B. rex, she searched the internet for an emu and ostrich owner site. Then she asked if anyone had birds that died recently during an egg-laying cycle. The outcome was a call from a South Carolina farmer and a decomposing ostrich that yielded the same kind of medullary tissue she saw in B. rex.
Evelyn Boswell, (406) 994-5135 or firstname.lastname@example.org