Wednesday, June 13, 2007

New Bird Ancestor Discovered

Palaeontologists have found a new bird-like dinosaur in China. Gigantoraptor erlianensis had a toothless beak and feathered arms and was about 26 feet long and 16 feet tall. (A skull and model are pictured at right) The fossil dates from the end of the Cretaceous Period. The large size of this species took the scientists by surprise.

Paleontologist Xing Xu of Beijing's Institute of Vertebrate Paleontology and Paleoanthropology and colleagues discovered the animal while prospecting for fossils in the Erlian Basin of the Gobi Desert in north-central China. Based on its size, the paleontologists initially classified it as member of the tyrannosaur lineage, but bits of beak, leg and other bones revealed that it more properly belonged to the oviraptorosauria group, heretofore a grouping of small, feathered creatures weighing only a few pounds. "It is the largest known beaked dinosaur," Xu says. Adds paleontologist Mark Norell of the American Museum of Natural History in New York City: "I was just flabbergasted when I saw it because it was so big."

The finding complicates the evolutionary descent of birds from dinosaurs. "Progressively from within advanced theropods you get smaller and smaller towards birds," Norell says. But "after some species originate and spring off the bird line, you get secondary gigantism."


Already, Gigantoraptor is proving very odd, according to the paper detailing the find published in Nature. It bears a ridged humerus (upper arm bone) never before observed in a dinosaur as well as an enormous but birdlike femur (thighbone). "Maybe it has some sort of birdlike running mechanism," Xu says. Norell adds: "We don't know the biomechanical advantage this would confer. But I don't think it's hopping around at that size."
See also this slideshow of Gigantoraptor images. There is more discussion from Grrlscientist.