Paleontologists working in northwestern Patagonia have unearthed the nearly complete skeleton of a small dinosaur whose bird-like 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-sized 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 Makovicky, dinosaur curator of Chicago's Field Museum and lead author of a report on the find published Wednesday in the journal Nature. "The evidence is that we have a distinct (dromaeosaurs) lineage -- 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 well-known 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 creature Buitreraptor gonzalezorum, after brothers Fabian and Jorge Gonzalez, who found the fossil.
Before 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 the evolutionary lineage that produced modern birds. Archaeopteryx, regarded as the first true bird, is about 145 million years old, while the feathered raptors of Liaoning, China, are dated at 130 million years.
While 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 the time when Earth's single land mass split into northern and southern pieces.
"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, heron-like skull and teeth without serrated edges, like a steak knife. "These are unusual features, and we think we have a predator of small prey," he said, possibly one that dined on small snakes prevalent in the region.
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."
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 also shared characteristics with an unusual 65-million-year-old fossil from Madagascar known as Rahonavis -- thought to have been a primitive, long-tailed bird.
By Guy Gugliotta
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