How Did Duck Billed Dinosaurs Get Through Dark, Polar Winters?
Researchers from the University of Cape-Town, the Museum of Nature and Science in Dallas, and Temple University have discovered that duck-billed dinosaurs endured long, dark polar winters. These dinosaurs lived within Arctic latitudes approximately 70 million years ago, and rather than migrating south for the harsh winters, they simply stayed put.
The paper, entitled “Hadrosaurs Were Perennial Polar Residents,” was published in the journal The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology. The study was funded by a grant from the National Science Foundation (NSF).
Anthony Fiorillo, a paleontologist at the Museum of Nature and Science, dug up Cretaceous Period fossils in Alaska’s North Slope. While some of the bones found were those of the horned dinosaur Pachyrhinosaurus, most of them were the bones of the duck-billed herbivore, Edmontosaurus.
In order to determine how these dinosaurs lived in such cold, polar regions, Fiorillo took a microscopic look at the structures of the dinosaur’s bones. With Allison Tumarkin-Deratzian’s help, an assistant professor of earth and environmental science at Temple, he analyzed the thin layers of the dinosaur’s bones microstructure.
Working independently, Anusuya Chinsamy-Turan, a professor of zoology at the University of Cape Town also analyzed the Edmonstosaurus’ bone structure and fossils. Realizing their findings were quite similar, they decided to collaborate and combine their data to assemble a larger data set for sampling. Half of the sampling was done in Temple, while the other half was done in South Africa.
“The bone microstructure of these dinosaurs is actually a record of how these animals were growing throughout their lives,” said Tumarkin-Deratzian. “It is almost similar to looking at tree rings.”
The researchers found bands of fast and slow growth that seemed to indicate a pattern.
“What we found was that periodically, throughout their life, these dinosaurs were switching how fast they were growing,” said Tumarkin-Deratzian. “We interpreted this as potentially a seasonal pattern because we know in modern animals these types of shifts can be induced by changes in nutrition. But that shift is often driven by changes in seasonality.”
The researchers then estimated there could be two reasons to explain why these dinosaurs were under such stress at different times in the year. Either they were enduring long winters or embarking on a long migration south.
After doing microstructure analysis on similar duck-billed dinosaurs in Canada, they found these creatures didn’t have similar stress patterns. This meant the Canadian duck-billed dinosaurs didn’t endure such seasonal periods of stress.
“We had two sets of animals that were growing differently,” said Tumarkin-Deratzian.
Fiorillo then examined the geology of the bonebeds in Alaska where the samples were excavated and found the fossils had been preserved in flood deposits.
“They are very similar to modern flood deposits that happen in Alaska in the spring when you get spring melt water coming off the Brooks Mountain Range,” said Fiorillo. “The rivers flood down the Northern Slope and animals get caught in these floods, particularly younger animals, which appear to be what happened to these dinosaurs.”
Since the floods came after periods of long, dark winters, this means the dinosaurs wouldn’t have been migrating at this time.
“It is fascinating to realize how much of information is locked in the bone microstructure of fossil bones,” said Chinsamy-Turan. “It’s incredible to realize that we can also tell from these 70 million-year-old bones that the majority of the polar hadrosaurs died just after the winter season.”