From the famed fossil locality Ukhaa Tolgod in the Gobi Desert of southern Mongolia, researchers have unearthed the remains of a pigeon-size bird that patrolled the skies some 80 million years ago. This beautifully preserved fossil bird, dubbed Apsaravis ukhaana, apparently represents a poorly known part of the avian evolutionary tree near the origin of all living birds. Paleontologist Mark Norell of the American Museum of Natural History in New York City and Yale University doctoral candidate Julia Clarke published a description of Apsaravis today in the journal Nature.
"All of the birds living today have a most recent common ancestor that they share," Clarke explains. "This fossil is just outside the group, or 'clade,' that includes the descendants of that common ancestor. It is the best preserved specimen of a fossil from close to the radiation of all living birds discovered in over 100 years." As such, Apsaravis is shedding light on the evolution of flight. Indeed, this fossil displays the oldest evidence yet of the muscle arrangement that enables modern birds to transition from the upstroke to the downstroke.
The fossil also reveals surprising ecological information. Researchers had suggested that the closest relatives of living birds, the ornithurines, were pushed out to near-shore and marine habitats by another lineage of birds, the Enantiornithes, which were thought to have dominated the land during that time. Apsaravis, however, is an ornithurine, and it turned up in terrestrial deposits. Thus, it appears that the ornithurines of 80 million years ago were already occupying the wide range of habitats filled by birds today.