New "Mini" Dinosaur a Step in Bird Evolution Path
Kevin Holden Platt
for National Geographic News
|September 6, 2007|
An 80-million-year-old fossil recently uncovered in the Gobi desert could be a key piece of the evolutionary puzzle of how massive dinosaurs gave rise to today's comparatively tiny birds, paleontologists say.
The newfound species, dubbed Mahakala omnogovae, measures just 27.5 inches (70 centimeters) from its head to the tip of its feathered tail.
Dinosaur digs over the last decade—including many in China—have suggested that several of the ancient reptiles were covered in feathers, a hint of their potential link to birds.
(Related: "Massive Birdlike Dinosaur Unearthed in China" [June 13, 2007].)
But few of the fossils have provided direct evidence of the evolutionary changes that led to flight.
Mahakala's small size bolsters the idea that some theropods, or bipedal carnivorous dinosaurs, decreased in stature during the evolutionary transition into birds, according to the team of paleontologists who discovered the young adult fossil.
"Miniaturization has long been considered crucial to the origin of flight," said Alan Turner of New York's American Museum of Natural History.
"Now Mahakala is providing the first signs of some of these early evolutionary steps."
Turner and colleagues will present their findings in tomorrow's issue of the journal Science.
The Mahakala fossil was found in the southern part of the Gobi in Mongolia and was named after a Tibetan Buddhist protector deity.
Paleontologists reconstructed Mahakala based on fossilized portions of the dinosaur's skull and limbs along with most of its spinal column.
The fossils indicate that the new species was not only feathered but also likely had winglike forelimbs and hind limbs, Turner said.
Mark Norell is a study co-author and curator at the natural history museum's division of paleontology.
"Many of the animals that were thought to look like giant lizards only a few years ago are now known to have been feathered and to have had many other defining bird characteristics," Norell said.
Mahakala is an offshoot of the group of meat-eating dinosaurs known as dromaeosaurids, which includes the Velociraptor featured in the 1993 movie Jurassic Park.
If Steven Spielberg were to make another Jurassic Park sequel, Turner noted, many of the dinosaurs that starred in the original film would require a complete makeover.
"The Velociraptor would be completely covered in feathers," he said.
Xu Xing, one of China's leading dinosaur hunters and an expert on the evolution of feathered dinosaurs, said that the new find fits perfectly into the theory that dinos evolved into birds.
"The discovery of Mahakala and other small birdlike dinosaurs is helping paleontologists paint new details on the mosaic depicting the first flight-capable birds' ascent from nonavian dinosaurs," said Xu, who was not involved in the new study.
Today consensus is building among paleontologists that dinosaurs and birds are linked.
But the experts disagree over how that evolutionary twist helped ancient birds escape being wiped out with the rest of the dinosaurs 65 million years ago.
"Paleontologists really don't know the answer to that. Why some animals survive mass extinctions while others don't is one of the most difficult questions in paleontology," lead study author Turner said.
"Flying doesn't seem to have hurt birds, yet pterosaurs—which are not dinosaurs—flew but went extinct."
Xu added that a combination of birds' ability to fly and to evolve quickly might have helped them survive.
"Birds mature within one year, and that gives them the means to adapt very rapidly to big changes in the environment," he said.
"They evolve much more quickly than massive dinosaurs or humans."
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