Archaeopteryx, widely regarded as being the world's oldest known bird, has just been knocked off its scientific perch, since new research concludes this feathered animal was, in fact, a dinosaur.
The study, published in the latest issue of the journal Nature, falls on the 150th anniversary of Archaeopteryx's discovery. This part avian, part reptile-looking animal was found less than two years after Darwin's groundbreaking "Origin of Species" was released. It quickly became a memorable visual symbol of evolution at work.
With Archaeopteryx likely removed from the bird family tree, a few other prehistoric species now become the world's oldest known birds.
"Epidexipteryx and Epidentrosaurus, two species we described years ago, are probably the most primitive and oldest known birds," lead author Xing Xu told Discovery News, adding that they lived about 160 million years ago at what is now Dahugou Locality in eastern Inner Mongolia.
Xu, a professor at the Chinese Academy of Sciences' Institute of Vertebrate Paleontology & Paleoanthropology, and his team made the determination about Archaeopteryx after analyzing their latest fossil discovery -- the remains of a small, long-armed, and four-winged predatory dinosaur that weighed less than 2 pounds. It is one of the tiniest dinosaurs ever found.
Named Xiaotingia zhengi, this new small dinosaur from western Liaoning, China, lived approximately 160 million years ago.
"This dinosaur is similar to Archaeopteryx in general body plan, (with its) similarly shaped head, shoulder girdle, long and robust arms, similarly shaped pelvis, and feet with an initially developed highly extensible second toe," Xu said. "(Both dinosaurs) came from the same family, the Archaeopterygidae, and our analysis shows that Archaeopteryx is slightly more primitive."
Birds are still regarded as being dinosaurs, so it is difficult to tease apart these non-avian dinosaurs from birds since many shared similar features, such as feathers and wings.
It appears that several dinosaur lineages experimented with feathers and flight, from an evolutionary standpoint. It remains a mystery why all such animals did not survive the big K-T extinction event about 60 million years ago, but Xu suspects the small size, flying capability and warm-bloodedness of some species permitted them to survive, giving rise to the ancestors of modern birds.
"We scientists use the cumbersome and seemingly pedantic 'non-avian dinosaurs' (term), but back about 150 million years ago, all these groups were extremely similar," Lawrence Witmer told Discovery News.
Witmer, a professor of anatomy and paleontology at Ohio University, supports the conclusions of Xu and his team, including that Epidexipteryx and Epidentrosaurus are now among the chief candidates for the "world's oldest known bird" title.
"We're getting so close to the point of actual origin (of birds) that the differences among these species are increasingly trifling the further back we go," Witmer explained.
He added, "It's a stunning affirmation of evolution…and it's sort of fitting that Archaeopteryx, the emblem of evolution since Darwin's time, is still part of the story."