Autumn 2009: Of Note
Drawing: James Hays, Fernbank Museum
Paleontologist finds evidence that burrowing behavior was widespread
By Carol Clark
Burrowing into the earth might have allowed some dinosaurs to survive extreme climate changes, believes Emory paleontologist Anthony Martin.
On the heels of his discovery in Montana of the first trace fossil of a dinosaur burrow, Martin has found evidence of more dinosaur burrows—this time on the other side of the world, in Victoria, Australia.
The find, which was published in Cretaceous Research, suggests that burrowing behaviors were shared by dinosaurs of different species, in different hemispheres, and spanned millions of years during the Cretaceous Period, when some dinosaurs lived in polar environments.
“This research helps us to better understand long-term geologic change and how organisms may have adapted as the Earth has undergone periods of global cooling and warming,” says Martin, a senior lecturer in environmental studies.
In collaboration with colleagues, Martin identified the ninety-five-million-year-old skeletal remains of a small adult dinosaur and two juveniles in a fossilized burrow in southwestern Montana in 2006. They later named the dinosaur species Oryctodromeus cubicularis, or “digging runner of the lair.” The researchers hypothesized that, besides caring for young in their dens, burrowing may have allowed some dinosaurs to survive extreme environments.
A year after the Montana find, Martin traveled to the Victoria coast, which marks the seam where Australia once nestled against Antarctica. Lower Cretaceous strata of Victoria have yielded the best-documented assemblage of polar dinosaur bones in the world. During a hike to a remote site known as Knowledge Creek, west of Melbourne, Martin rounded the corner of an outcropping and was astounded to see the trace fossil of what appeared to be a burrow. “In paleontology, the saying, ‘where luck meets preparation’ really holds true,” he says.
The probable burrow etched into the Early Cretaceous outcrop was about six feet long and one foot in diameter. It gently descended in a semi-spiral, ending in an enlarged chamber. Martin later found two similar trace fossils in the same area.
The Victoria fossils are about 110 million years old, originating around the time that Australia split with Antarctica, and dinosaurs roamed in prolonged polar darkness along forested southern Australia river plains. It was one of the last times the Earth experienced global warming, with an average temperature of 68 degrees Fahrenheit—about 10 degrees higher than today. During the polar winter, though, the temperature could plunge below freezing.
Previously, researchers theorized that the small dinosaurs in the region survived harsh weather by sheltering beneath large tree roots or in hollows. Martin’s find, however, indicates that they may have dug into the soft banks of rivers flowing out of the rift valley.