Dinosaur Jr., For Real

Dinosaurs are often thought of as giants of the Earth. But on an island in what is now Europe, 150 million years ago, petite dinosaurs ruled. In this environment, Sauropods, known to reach 80 feet in length in other parts of the world, were instead "island dwarves." Island life made them roughly the same size as a modern horse. The phenomenon has been getting attention elsewhere to explain a new species of tiny humans. Experts say the case is also an example of how much more dinosaur experts are learning by doing the unthinkable: cutting open dinosaur bones.

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ROBERT SIEGEL, host:

There was a time when being really big was in fashion. The age of the dinosaurs. The biggest of the big were the Sauropods. Sometimes called the cows of the Jurassic, they were long-necked giants that grazed on plants and shook the earth when they walked. But it appears that there was a strange population of petite Sauropods. The bones of some of these creatures have been found in Germany.

NPR's Christopher Joyce has the story of the shrunken Sauropods.

Petite is a relative term. The bones in Germany were from animals the size of draft horses. Each animal would have weighed a ton or so, but then a normal Sauropod weighed 10 to 15 times that, with a tail the length of a school bus. How dinosaurs got small hasn't been a common question among paleontologists. It's how they got big that's the hot topic.

Dr. MARTIN SANDER (University of Bonn): They ask how do you blow up your dinosaur and we ask how do you shrink your dinosaur.

JOYCE: Martin Sander, at the University of Bonn, is the paleontologist who took on this odd case of miniaturization. He applied a new technique that's revolutionizing dinosaur research. He reads the microscopic patterns inside dinosaur bones. These patterns are something like tree rings. They tell how fast and how long an individual dinosaur grew. Sander concluded that these bones belong to fully grown, adult Sauropods, not babies.

Dr. SANDER: It's really the smallest of the giants. I mean, Sauropods in general are the biggest animals that ever evolved on land. Only whales in the sea are bigger. And this one is by far the smallest.

JOYCE: So how did they get small? Sander believes it was island dwarfing. About the time these animals lived, some 150 million years ago, sea level rose and isolated patches of land into islands.

Dr. SANDER: And then the animals on these land masses either die out or they adapt by shrinking. It makes sense that we would find them in Europe, because only Europe at this time was this archipelago full of islands.

Dr. KRISTI CURRY ROGERS (Macalester College): And if you live on an island, you don't really want to grow to be enormous.

JOYCE: Kristi Curry Rogers is a Sauropod expert at Macalester College in Minnesota.

Dr. ROGERS: Because you're going to run out of resources really quickly, especially if you grow at the rates that we know Sauropods in general did.

JOYCE: By slowing down their growth rate, the Sauropods stayed smallish. That way, they ate less and they thrived. Now that's fine, until you remember there were other dinosaurs at the time that dined on anything that breathed, the big meat-eating predators. Rogers says normal Sauropods that lived on the continents were probably too big for most predators to bring down, kind of like the elephants of the Serengeti. But what about these island dwarfs?

Dr. ROGERS: These Sauropods, I hope, had predators that were scaled to their size. But I haven't heard of anything that would actually definitely show that.

JOYCE: Sander, who describes the research in the journal Nature, says it's likely that all the dinosaurs on these islands, even the predators, were downsized as well, creating what you might call a Euro-sized Jurassic Park.

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