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Digging Dinosaur Discovered Inside Fossil Den

James Owen
for National Geographic News
March 21, 2007
 
Some dinosaurs lived underground, say U.S. fossil hunters who today announced the discovery of the first known burrowing dino species.

Fossils of the new dinosaur were found in southwestern Montana in a tunnel the creature dug some 95 million years ago, paleontologists report.

Named Oryctodromeus cubicularis ("digging runner of the den"), the newfound species shows that some dinosaurs could live down holes and that they gave extended care to their young, according to a team led by paleontologist David Varricchio of Montana State University in Bozeman.

Digging ability in dinosaurs also suggests they could survive harsher environments than previously thought, the team says.

Details of the find appear in the latest issue of the journal Proceedings of the Royal Society B.

Remains of an adult and two juveniles were first unearthed in 2004 in a fossil den similar in appearance to those of burrowing mammals alive today, the team said.

Numerous smaller tunnels branching from the main den indicated that insects such as bees and possibly mammals also shared the dinosaurs' lair.

Oryctodromeus is described as a swift, two-legged plant-eater that weighed up to 70 pounds (32 kilograms) and measured 6.9 feet (2.1 meters) long.

The width of the dinosaur matched that of its tunnel, which measured some 11.8 inches (30 centimeters) across.

Digging Features

The small dinosaur shows several specializations for burrowing, the team reports, including a modified snout that could be used like a shovel, large bony attachments on its shoulders that held powerful muscles, and strong hips for bracing itself while digging.

The size of the two fossil juveniles indicates that they remained in the den for at least several months, providing some of the best evidence yet for dinosaur parental care, the team said.

Kevin Padian of the Museum of Paleontology at the University of California, Berkeley, said the discovery represents the first ever record of a burrowing dinosaur.

"It seems to have kept its young protected from predators in this way," he said.

In a review of the find published in the same journal, Padian noted that finds of dinosaur eggs and nests indicate that some species hatched in an immature condition, suggesting they had to be fed and looked after for some time.

(Related story: "Dinosaurs Were Doting Parents, Fossil Find Suggests" [September 8, 2004].)

Padian also noted that fossils of species related to Oryctodromeus appear to share some of its specializations, suggesting that burrowing behavior may have been more widespread in this group of dinosaurs.

Study team member Anthony Martin of Emory University in Atlanta says the discovery may lead to other burrowing dinosaurs being identified.

"A lot of people will go back and re-look at their little dinosaurs," he said.

While no previous fossil evidence for such dinosaurs is known, Martin said, a study last year reported similar-size animal tunnels in dino-era sand sediments in south-central Utah.

Burrow Benefits

Burrowing behavior may have enabled dinosaurs to survive more extreme conditions than previously thought, the paleontologist added.

Underground dens provide animals a more constant environment in terms of temperature and humidity.

"Think how many desert animals burrow," Martin said. "But also think about polar habitats. To me that's the most fascinating aspect."

So-called polar dinosaurs recently found in southeastern Australia are of a similar type to the new species, Martin said.

(Related story: "Researchers Melt Polar Dinosaur Mysteries" [February 25, 2002].)

"It makes you wonder: Did they also burrow to escape some of the harsh conditions of the polar winter?" Martin said.

"That's one example of where we might take a look at those dinosaurs again."

The Montana fossil find also raises questions about dinosaur-extinction theories that suggest the creatures were wiped out 65 million years ago by a massive asteroid impact or volcanic eruption.

One of the reasons put forward for dinosaurs not surviving such an event is that, unlike other animals, they couldn't burrow.

"Well, now we have a few dinosaurs that could," Martin said. "It's something to think about."

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