Feathered dinosaur older than earliest bird

by Colin Barras for New Scientist

25 September 2009

The record for the oldest feathered dinosaur, which has stood for almost 150 years since the discovery of Archaeopteryx, has finally fallen to an even older fossil unearthed in China, shedding new light on the origin of birds. The first full skeleton of Archaeopteryx, "that strange bird" as Darwin described it, was discovered in the Jurassic limestone of Solnhofen, Germany, just two years after the publication of On the Origin of Species. It has remained something of an evolutionary anomaly ever since. Spectacular feathered dinosaurs discovered in the last decade or so show clearly how a small group of theropod dinosaurs gave rise to the first birds, but these specimens are almost exclusively Cretaceous in origin, at least 20 million years younger than Archaeopteryx. Feathered dinosaurs pre-dating Archaeopteryx have remained elusive, largely because the Jurassic theropod fossil record is so poor. The closest palaeontologists have come to a feathered dinosaur older than Archaeopteryx is Pedopenna, discovered in Inner Mongolia in 2005. But there's some confusion over exactly how old the Inner Mongolian sediments are, and it's likely that Pedopenna is actually slightly younger than Archaeopteryx.

Not so the new Chinese find Anchiornis huxleyi, the latest of a number of specimens found in the past year and the first to sport feathers. It comes from the Tiaojishan formation of Jianchang county, recently dated to between 161 and 151 million years old and therefore older than the 150-million-year-old Archaeopteryx-bearing German rocks. Anchiornis possesses well-developed feathers on all four limbs, a trait that would have seemed bizarre if the fossil had been discovered a decade ago. But palaeontological finds in recent years suggest the four-wing pattern may have been the rule rather than the exception in proto-birds – both Microraptor, discovered in 2003, and Pedopenna have feathered hind limbs. "Current data suggests that the four-winged condition evolved probably once at the base of the Paraves, a group containing dromaeosaurids [the dinosaur family containing Microraptor], troodontids [the dinosaur family to which Anchiornis belongs], and birds," says Xu Xing of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who discovered Anchiornis.

The new find comes from a "critical stage along the line to birds", Xu adds. "Probably the evolution of longer and stronger fore wings [ultimately] made the hind wings unnecessary." Anchiornis is the oldest of the three, but its feathers are "smaller, symmetrical, different from typical flight feathers", according to Xu, making it unclear whether the animal could fly. It has unusually long legs suggestive of running, although the long leg feathers may have made rapid movement problematic. "This is something confusing," says Xu. "Although when you get close to the transition point from dinosaurs to birds, you get very unusual combinations of features." Alan Feduccia, a palaeo-ornithologist at the University of North Carolina, Chapel Hill, says the new fossil species adds a "dazzling new piece to the complicated puzzle of early bird evolution", showing just how blurred the distinctions are between groups in this area of the dinosaur evolutionary tree.

[As I’m reading a book about Evolution at the moment…..]