BEIJING, Sept. 26 (Xinhua) -- Scientists say a 419-million-year-old fossilized fish may be the oldest known creature with a modern type of jaw, and the discovery may mark the first time the complete set of human face bones have appeared in the evolutionary history.
Previous fossil records traced human's opposing jaws to the class of bony fish, but the discovery of Entelognathus primordialis in China's Yunnan Province suggests the bones emerged earlier in the now extinct group of placoderms, according to a paper on Thursday's issue of the journal Nature.
The article's first author, Zhu Min of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, describes the fish as measuring about 20 cm, with the placoderms' signature body armor but with the jaw of a bony fish.
"It suggests the fish is near the top of the placoderm class, when some members of the class began to develop features of the bony fish, including its jaw," Zhu said.
According to Zhu, the fish had jaw bones including dentary, premaxilla and maxilla that, when combined with other bones, correspond to the entire bone structure of modern human face for the first time.
Zhu said the finding also showed a direct evolutionary link between placoderms and bony fish, overthrowing previous theories suggesting acanthodians as a transitional stage between the two classes.
Bony fish encompasses the vast majority of extant fish species and is the common ancestor of humans and other terrestrial vertebrates.