BOSTON — A 110-million-year-old fossil from the south of Italy is giving scientists the fullest picture yet of why dinosaurs dominated animal life for eons.
For millions of years, predators like velociraptor and Tyrannosaurus rex ruled the earth. Now, the Italian fossil - called a Rosetta stone of paleontology by some researchers - is yielding fresh insights into why the animals were such effective hunters. At the same time, the scientists responsible for one of the first detailed studies of the specimen say it throws doubt on a theory held by many paleontologists: that birds are the direct descendants of theropods such as velociraptors - the villains of "Jurassic Park."
"This is the most spectacular fossil ever found," says John Ruben, an Oregon State University zoologist who headed the US-Italian team that examined the creature. Unlike most fossils, he explains, this one displays internal organs and even some muscle fibers, in addition to the creature's skeletal structure. Thus, he says, it's possible to study biological features that until now could only be inferred from bone structure.
The fossil was first reported last March in the journal Nature by Italian paleontologists Cristiano Dal Sasso and Marco Signore, who also took part in Dr. Ruben's study. It was discovered near Salerno, Italy, in the early 1980s by rockhound Giovanni Todesco, who thought the creature was a bird.
Years later, he saw "Jurassic Park." Its beaked velociraptors prompted him to take out his old find and give it a closer look. Suspecting it might be a small dinosaur, he turned it over to paleontologists, who immediately saw its significance. Indeed, the researchers say, the creature is similar to a velociraptor.
Last July, Oregon State's Ruben traveled to Salerno with graduate students Terry Jones and Nicholas Geist to examine the creature's fossilized internal organs to see what they would tell them about how it functioned. Their report appears in yesterday's edition of the journal Science.
One of the most striking features of the baby theropod, known as Scipionyx samniticus, was the body cavity's separation into two compartments - one for the heart and lungs, the other for the liver and digestive system.
Today, the researchers say, that kind of structure is seen only in animals that have active diaphragms to help move air into their lungs, such as mammals or crocodilelike reptiles.
Moreover, the placement of the lower organs and the structure of the pelvis suggested that S. samniticus's diaphragm was pumped with a piston-like motion similar to that of modern crocodilians.
With that kind of breathing apparatus, such dinosaurs were unlikely to be sluggish animals, according to Mr. Geist. Instead, he says, "what you have is a turbocharged reptile."
Indeed, Ruben adds, the creature combined the best metabolic traits of cold-blooded animals and of warm-blooded animals.
Like cold-blooded creatures, S. samniticus used very little energy when resting. But with the breathing mechanisms of warm-blooded creatures, it could use its reserves of stored energy to run down prey over fairly long distances.
Ruben says the dinosaur's metabolic traits were particularly well-suited to the climate of the times. Temperatures in that period were warmer than today, and there were little seasonal changes. Once the climate cooled and seasonal changes grew more extreme, S. samniticus would have had a difficult time adapting.
Not bird ancestors?
According to Ruben's team, the fossil's lungs and other features bear little resemblance to today's birds, leading the researchers to conclude that if birds did descend from dinosaurs, such ancestors would be unlike any known dinosaurs.
"My best guess is that, yes, there may be close relationships between birds and dinosaurs," Ruben says. But based on his study of S. samniticus, "we can't derive birds from any known theropods."
Yes they are
Yet others suggest that Ruben's conclusion fails to focus on the broader range of evidence supporting the link between birds and dinos we know. Birdlike features appear even in S. samniticus, they say - its breast bone, for example, or evidence of locations where birdlike air sacs invade the skeleton.
Rather than excluding known dinosaurs from the lineage of modern birds, S. samniticus may well represent one point in an evolutionary transition from piston-driven lung structures to a more birdlike breathing apparatus, says Jacques Gauthier, curator of the Peabody Museum of Natural History at Yale University in New Haven, Conn.
"This is the beauty of the fossil record, to show us a world that no longer exists," he says. "It allows us to tease part traits and their sequence of acquisition."