Dinosaur find is no hollow feat

It took some guts to drill a hole in a 65-million-year-old dinosaur bone. But the best imaging technology could not penetrate the bone's interior secrets, and Kristi Curry Rogers found herself looking at a blank picture of its internal structure.

It was only when the drill bit fell inside that the Macalester College paleontologist realized the massive, sweet potato-shaped bone was hollow.

The discovery, published Tuesday in the online journal Nature Communications, may help solve one of the many biological mysteries about some of the more mesmerizing creatures to ever roam the Earth: How did they survive extreme swings in weather?

The dinosaur, a 50-foot-long Rapetosaurus from the African island of Madagascar, probably used the bone as a reservoir for vital minerals like calcium, which it needed to survive and reproduce, Curry Rogers theorizes.

This type of bone, embedded within the creature's skin, is often found in dinosaur skeletons and even in some modern-day reptiles. Called osteoderms, they have many uses, from protection to temperature regulation to buoyancy.

But Curry Rogers and her colleagues, who have been studying a treasure trove of dinosaur bones on the grassy plains of northwest Madagascar since the 1990s, were puzzled to find this particular hollow bone in one of the large, long-necked dinosaurs found there.

"These bones have always been problematic," she said. "When you find a humongous osteoderm on a skeleton that was 50 feet long, it doesn't make sense."

It's the kind of scientific mystery that has engaged Curry Rogers since she was 7 years old and decided to become a paleontologist.

At the site in Madagascar, which was once a river, she and her colleagues found lots of osteoderms. The area had huge swings in rainfall in the age of dinosaurs, and still does. During the long, frequent droughts the animals gathered at the river for water -- and died there in huge numbers when it dried up.

When the rain came again, their bodies were buried in mud, the ideal tomb for their bones.

"They are in the perfect place to be captured in the fossil record," she said.

The area now has thousands of "bone beds," which accumulated during a thousand-year period near the end of the dinosaur era. It was here that Curry Rogers and her co-researchers first found and identified Rapetosaurus as a new species of dinosaur, one of the biggest to ever walk on land.

But in 1998 they also found these odd bones. They found one with an adult skeleton and a few others with skeletons at different stages of growth. Unlike other dinosaurs that used osteoderms for armor, or reptiles that used them for temperature control, Rapetosaurus had no apparent need for hollow bones, she said.

But years later, after the bones had been extracted, cleaned, processed and shipped to the Field Museum in Chicago, she found that the adult osteoderm was hollow, while those from the younger skeletons were not.

She had her answer. The dinosaurs used them over their lifetimes in much the way camels use their humps -- for long-term storage of minerals, she said.

During times of drought or starvation, the dinosaurs could not live if they had to drain minerals from their arm and leg bones, she said.

"They weighed tens of tons," she said. "No way could they pull minerals from their limbs and still be able to walk. They would fracture their bones."

It's a theory at this point, but it's also a small contribution to the much larger dilemma that is just as relevant today as it was 65 million years ago, she said. Extreme swings in weather and environment shaped the fate of the dinosaurs and are shaping the modern world, too.

"It gives us perspective on our own place and our fragile ecosystem," she said.

Josephine Marcotty • 612-673-7394