Fossil Hints at How Flight Took Wing
A birdlike dinosaur found in Argentina may offer a connection between earth-bound reptiles and birds
When teenager Augustine Scanferla first held out the sun-bleached bone, Fernando Novas was inclined to dismiss the student's find as modern-day turtle remains. After all, says the Argentine paleontologist, such remains are common in the badlands of Patagonia, where his fossil-hunting team had spent nearly 25 days toiling under a hot January sun.
Almost immediately, however, other members of the team found related bits and pieces nearby that taken together, he says, clearly signaled "dinosaur."
The three-day digging marathon that followed unearthed the oldest bird-like dinosaur yet. The more than 20 bones and fragments the team found already are providing scientists with vital clues about how modern birds evolved from their prehistoric predecessors.
Using the Mapuche Indian phrase meaning "half bird from northwest Patagonia," Dr. Novas and his colleagues named the 90-million-year-old beast Unenlagia comahuensis.
The meat-eating creature, described in the current issue of the journal Nature, is much younger than the 145 million-year-old fossil remains of the oldest known bird, Archaeopteryx. But elements of Unenlagia's skeleton bear striking similarities to those of Archaeopteryx, prompting researchers to view the new find as a descendant of a missing link between ancient two-legged predators and the oldest known bird.
A 'living fossil'
"This new fossil was a living fossil in its own day," says Hans-Dieter Sues, a paleontologist at the Royal Ontario Museum in Toronto. "This is a very exciting find."
It didn't start out that way. When Novas's team finished collecting the fossil specimens from the arid Patagonian hillside a year and a half ago, "I supposed that this was a common dinosaur, but no more," he says in an interview from the headquarters of the National Geographic Society in Washington, which helped pay for his expedition.
The surprise came five months later, after another paleontologist, Pablo Puerta, stabilized and prepared the fossilized bones for study at his lab at the Museo Paleontologico Egidio Feruglio in Trelew, Argentina.
When Dr. Puerta took the treated remains to Novas's office in Buenos Aires, "he put the bones on my desk. The pelvic [bones] were so similar to the oldest known bird that we realized this was no common dinosaur, but something really special," Novas says.
Based on their study of the fossil, the two scientists pieced together an outline of Unenlagia, which they estimate stood about 1.2 meters (3.9 feet) tall at the hip and was about 2.3 meters long. Two parts of the carnivore's anatomy of particular interest, he says, are the pelvis area and the forearms.
Like Archaeopteryx, Unenlagia has a very robust hip structure, which Novas says "could be a prerequisite not only to fly, but to land in trees or on rocks without breaking any bones."
But of particular interest, Dr. Sues says, is the shoulder area. "The shoulder girdle and upper arms are identical to birds" and were positioned in such a way that Unenlagia literally could flapped its arms and tuck them at its side much as a bird does its wings.
Researchers speculate that Unenlagia's ancestors probably used these abilities to balance themselves as they ran and hopped after prey.
These winglike features in a ground-based dinosaur are likely to fuel the debate over whether flight originated from the ground up or evolved as tree-dwelling creatures developed an ability to glide from the trees down, adds Lawrence Witmer, a paleontologist at Ohio University in Athens, Ohio.
One reason the debate rages is that fossil evidence for gliding flight goes back at least 250 million years.
In March, Sues and two colleagues from the State Museum of Natural History in Karlsruhe, Germany, published a study in the journal Science that identified the means by which a 30-centimeter-long (11.8 inches) reptile was able to glide. The creature, Coelurosauravus jaekeli, failed to survive a mass extinction 250 million years ago. Its wings have a structure that has never been seen in fossils before or since: The hollow bones supporting the wings formed directly in the skin itself, rather than from converted forelimbs
Filling a gap
Whatever the outcome of the debate, it's clear that Unenlagia is filling an important gap, Novas says."If you are interested in bird evolution, you must study Archaeopteryx," he says. But the bird's fossils exist only as two-dimensional impressions in the sedimentary rock that encased them, preventing researchers from knowing with any certainty how Archaeopteryx moved.
"Now," he says, "we have a three-dimensional dinosaur that can inform us about those movements."