Chinese scientists have discovered a near-complete fossil fish from southwestern China that provides insight into the evolution of jawed vertebrates (gnathostomes).
Publishing the description of the fish as a new species, Guiyu oneiros, in a recent issue of the journal Nature, Min Zhu and coauthors describe a mix of derived and ancestral characters in the fish, considered to be a basal member of the Sarcopterygii (the lobe-fins, a group that includes lungfishes, coelacanths and tetrapods).
The mix of characters in Guiyu (the generic name means ghost fish in Chinese) points to a deep history for jawed vertebrates: the fossil is about 419 million years old (from the Silurian period) and suggests that the split between the Actinopterygii (ray-fins, including all modern bony fishes) and Sarcopterygii is at least that old.
For more information, see the paper: Zhu, M, W-J Zhao, L-T Jia, J Lu, T Qiao and Q-M Qu (2009) The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature 458, pp. 469"474.