Paleontologists working in northwestern Patagonia have unearthed the nearly complete skeleton of a small dinosaur whose birdlike appearance suggests that flight may have evolved twice -- not only in birds but also among the prehistoric raptors of the southern hemisphere.
The newly discovered fossil, of a rooster-size carnivore known as a dromaeosaur, lived 95 million years ago and is the oldest raptor ever found in the southern continents. Its discovery may signal that dromaeosaurs are much older than previously thought.
"We're really just scratching the surface," said Peter J. Makovicky, dinosaur curator of Chicago's Field Museum and lead author of a report on the find published yesterday in the journal Nature. "The evidence is that we have a distinct lineage [of dromaeosaurs] -- the southern lineage."
Makovicky and a team of Argentine paleontologists led by Sebastian Apesteguia of Argentina's Natural History Foundation collected the fossil from a famous site known as La Buitrera, "The Vulture's Nest," in Rio Negro province, about 700 miles southeast of Buenos Aires.
The team named the new find Buitreraptor gonzalezorum, after brothers Fabian and Jorge Gonzalez, who found the fossil. Prior to Buitreraptor, a few teeth and other bone fragments were the only dromaeosaur remains known in the southern hemisphere.
This scarcity contrasted sharply with the relatively abundant deposits in North America and Asia of such well-known dromaeosaurs as velociraptor, Utahraptor and smaller species unearthed in China.
Paleontologists generally regard the northern raptors, especially the Chinese fossils, as part of modern birds' evolutionary lineage. Archaeopteryx, regarded as the first true bird, is 145 million years old, while the feathered raptors of Liaoning, China, are dated at 130 million years.
Although Buitreraptor is considerably younger, its location deep in South America's southern cone suggests that dromaeosaurs generally may be 180 million years old, dating to when Earth's single land mass split into northern and southern pieces. Today's continental arrangement took form 70 million years ago.
"To say dromaeosaurs are 180 million years old is not a stretch at all," said paleontologist Matthew Lamanna of the Carnegie Museum of Natural History, in Pittsburgh. "You look at the fossil record and see Archaeopteryx is 150 million years old, so dromaeosaurs should already be around."
Makovicky noted, however, that unlike northern dromaeosaurs, Buitreraptor has a long, heronlike skull and teeth without serrated edges: "These are unusual features, and we think we have a predator of small prey," Makovicky said.
Lamanna said that the differences between the northern and southern species also come as no surprise. Once researchers established that dromaeosaurs were evolving on two separate super-continents, "the fact that they come to be different is what we would expect. It would have been surprising to find velociraptor in Patagonia."
On the other hand, Makovicky said Buitreraptor is clearly a dromaeosaur, displaying many typical characteristics, including a spiked middle toe for gutting prey, heavy hind limbs for fast running, a long tail and powerful forelimbs -- but not powerful enough to fly.
Makovicky and the research team also noticed that Buitreraptor shared characteristics with an unusual 65 million-year-old fossil from Madagascar known as Rahonavis -- thought to have been a primitive, long-tailed bird.
"It looks like Archaeopteryx, but if you examine the hip region, it pushes them toward the dromaeosaurs," Makovicky said. "So now we have evidence that Rahonavis is not a bird, but perhaps a flying dromaeosaur."
This does not necessarily mean that Rahonavis evolved into a bird, Makovicky said. "It was probably an evolutionary dead end," he said, but its kinship with Buitreraptor "may indicate a second origin of powered flight," apart from the lineage that included Archaeopteryx and the northern raptors.