July 10, 2009
World’s Oldest Dinosaur Burrow Discovered In Australia
Paleontologists have discovered the world's oldest dinosaur burrows in Australia. The 106-million-year-old burrows are the first to be found outside of North America, and were much closer to the South Pole when they were created.
In total, three separate burrows have been discovered, the largest of which was about 6ft. long. Each burrow had a similar design and was just large enough to contain the body of a small dinosaur.
The discovery supports the theory that dinosaurs living in harsh, cold climates burrowed underground to survive.
The only other known dinosaur burrow was discovered in 2005 in Montana, and contained the bones of an adult and two young dinosaurs of a small new species called Oryctodromeus cubicularis. Two years after its discovery, scientists dated the burrow from 95 million years ago.
The older burrows in Australia were found by one of the researchers who made the original Montana discovery.
"Like many discoveries in paleontology, it happened by a combination of serendipity and previous knowledge," said Anthony Martin of Emory University in Atlanta.
"In May 2006, I hiked into the field site with a group of graduate students with the intention of looking for dinosaur tracks. We did indeed find a few dinosaur tracks that day, but while there I also noted a few intriguing structures," he told BBC News.
Martin returned to the site, known as Knowledge Creek about 150 miles from Melbourne, to study the structures in July 2007 and again in May of 2009.
He was astonished at what he found.
"I was scanning the outcrop for trace fossils, and was very surprised to see the same type of structure I had seen in Cretaceous rocks of Montana the previous year," said Martin.
That original structure was the burrow of O. cubicularis.
"So to walk up to the outcrop and see such a strikingly similar structure, in rocks only slightly older, but in another hemisphere, was rather eerie," Martin said.
Within the rock, which is part of the Otway group of rocks that have produced a large diversity of vertebrate fossils, Martin discovered three separate burrows less than 10 feet apart, two of which formed a semi-helix twisting down into the rock.
The largest and best-preserved burrow turns twice before ending in a larger chamber. Dubbed tunnel A, it is more than 6 feet in length. Martin calculates that an animal weighing around 22 pounds would have created each burrow. Twisting burrows can help keep predators at bay and provide a steady temperature and humidity environment.
Alligators, aardwolves, coyotes, gopher tortoises and striped hyenas are among the modern animals that make such burrows.
Although Martin isn't sure which species of dinosaur made the burrows, he noted how similar their designs are to the burrow created by O. cubicularis.
A number of small ornithopod dinosaurs, which stood upright on their hind legs and were about the size of a large iguana, were believed to have lived in the area during the same time in the Cretaceous period.
Martin has ruled out a number of other sources that could have created the burrows.
The fact dinosaurs created them makes sense, he said.
Australian researchers first proposed two decades ago that some dinosaurs might have created burrows to survive harsh climates they couldn't escape from by migrating.
"It gives us yet another example of how dinosaurs evolved certain adaptive behaviors in accordance with their ecosystems," Martin said.
"Polar dinosaurs in particular must have possessed special adaptations to deal with polar winters, and one of their behavioral options was burrowing. It provides an alternative explanation for how small dinosaurs might have overwintered in polar environments."
Martin hopes that paleontologists will be on the look out for dinosaur burrows, and for dinosaurs that are physically adapted to burrowing into soil.
The findings were published in the journal Cretaceous Research.
Image 1: Drawing by James Hays, Fernbank Museum
Image 2: Following his Montana discovery of the first trace fossil of a dinosaur burrow, Emory University paleontologist Anthony Martin has found evidence of older, polar dinosaur burrows in Victoria, Australia.
On the Net: