After decades of work, most paleontologists are now certain that birds evolved from dinosaurs. But another important question--the origin of modern birds--hasn't gotten as much attention, partly because fossil evidence has been frustratingly scarce. Now an 80-million-year-old bird from Mongolia may help relieve those long-standing frustrations--it's the best-preserved close relative of modern birds found in more than a century. "This fossil will be an incredible focal point for what we will know about bird relationships," says paleontologist Jim Kirkland of the Utah Geological Survey in Salt Lake City.
The most primitive bird known, Archaeopteryx, flapped over Jurassic lagoons some 150 million years ago. By the early Cretaceous, roughly 144 million years ago, a more advanced group of birds had appeared. Called the Enantiornithes, or "opposite" birds, for the way their foot bones grew, they flourished for 80 million years before going extinct. They were succeeded by the Ornithurae--the group that includes living birds--roughly 65 million years ago. But not many ornithine fossils are known, so paleontologists didn't know much about modern birds' earliest ancestors.
Now Julia Clarke of Yale University and Mark Norell of the American Museum of Natural History in New York City unveil Asparavis, a new fossil bird from the Ukhaa Tolgod region of Mongolia. Not only is the specimen a long-coveted ornithurine, but it is also breathtakingly well preserved. Asparavis is already turning up some surprises, the authors report in the 11 January Nature. For example, it shows that a dozen enantiornithine traits thought to be diagnostic of that group actually aren't. That means the dozen or so fragmentary fossils classed as Enantiornithes by those features may not belong to the group--and that could shake up the standard idea that Cretaceous enantiornithines were much more diverse than ornithurines.
No matter how these features shake out, paleontologists are thrilled to have such a complete bird to work with. "This specimen is paramount for understanding the origin of modern birds," says Luis Chiappe of the Natural History Museum of Los Angeles County.
Bird systematics and fossil record