WASHINGTON, Aug. 23 (Xinhua) -- Chinese and American researchers have discovered two new species of dinosaur in an expedition to China's Xinjiang, according to a study published on Thursday in the journal Current Biology.
The two new species named "Xiyunykus pengi" and "Bannykus wulatensis" are bird-like dinosaurs known as alvarezsaurs that share many characteristics with birds.
The bodies of alvarezsaurs are slender, with a bird-like skull and many small teeth instead of the usual large, sharp cutting teeth of their meat-eating relatives, according to the study.
"When we described the first well-known alvarezsaur, Mononykus, in 1993, we were amazed at the contrast between its mole-like arms and its roadrunner-like body, but there were few fossils connecting it back to other theropod groups," said James Clark, professor of biology at the George Washington University.
The alvarezsaurs did not always look this way, however, according to the researchers.
Early members of the group had relatively long arms with strong-clawed hands and typical meat-eating teeth. Over time, they evolved into dinosaurs with mole-like arms and a single claw.
The discovery of the new specimens lent clue to an important shift in how the specialized features of the alvarezsaurs evolved.
"It can be hard to pin down the relationships of highly specialized animals. But fossil species with transitional features, like Xiyunykus and Bannykus, are tremendously helpful because they link bizarre anatomical features to more typical ones," said Jonah Choiniere, an associate professor at Wits University and member of the research team.
"Our international field teams have been tremendously productive over the years," said Xu Xing from the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences. "This research showcases just some of our incredible discoveries."