Did dinosaurs survive climate extremes underground?

Evidence of ancient burrows in different parts of the world suggests dinosaurs might have survived cold Antarctic winters — even in a time of extreme global warming — by digging underground, according to a US researcher.

Emory University paleontologist Anthony Martin has discovered fossils of dinosaur burrows in both Montana and Victoria, Australia. He writes in this month’s Cretaceous Research that his findings suggest that burrowing behaviours 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,” said Martin, a senior lecturer in environmental studies at Emory. Martin is also an honorary research associate at Monash University in Melbourne.

In 2006, in collaboration with colleagues from Montana State University and Japan, Martin identified the 95-million-year-old skeletal remains of a small adult dinosaur and two juveniles in a fossilised burrow in southwestern Montana. They later named the dinosaur species Oryctodromeus cubicularis, meaning “digging runner of the lair.”

The researchers hypothesised that, besides caring for young in their dens, burrowing might have allowed some dinosaurs to survive extreme environments — which throws a potential wrench in theories that the dinosaurs died out as a result of cataclysmic global cooling in the wake of a giant asteroid strike.

One year after the Montana find, Martin discovered a similar fossil burrow in a remote site known as Knowledge Creek, west of Melbourne. During the Lower Cretaceous, that region of Australia once hugged Antarctica.

Despite the fact that global temperatures during that period 110 million years ago averaged 68 degrees Fahrenheit — about 10 degrees warmer than today — the Victoria dinosaurs roamed in prolonged polar darkness along the forested southern Australia river plains. During winters, temperatures could plunge below freezing.

Previously, researchers theorised that the small dinosaurs in the region survived harsh weather by sheltering beneath large tree roots or in hollows. Martin’s find, however, indicates they may have dug into the soft banks of rivers flowing out of the rift valley, huddling in burrows to avoid the cold.

The age, size and shape of the likely burrows led Martin to hypothesise they were made by small ornithopod dinosaurs — herbivores that were prevalent in the region. These ornithopods stood upright on their hind legs and were about the size of a large, modern-day iguana.

“It’s fascinating to find evidence connecting a type of behavior between dinosaurs that are probably unrelated, and lived in different hemispheres during different times,” Martin said. “It fills in another gap in our understanding of the evolution of dinosaurs, and ways they may have survived extreme environments.”