Entelognathus primordialis was an ancient fish that lived about 419 million years ago in the Late Silurian seas of China. The finding, detailed today (Sept. 25) in the journal Nature, provides a link between two groups of fishes previously thought to be unrelated, challenging long-held notions of how vertebrate faces evolved.

Nearly all vertebrates belong to the group of jawed vertebrates known as gnathostomes. Sometime in the past, the gnathostome family tree branched into two groups: cartilaginous fish (Chondrichthyes) such as sharks and rays, and bony fish and four-limbed animals, including humans (Osteichthyes). [See Photos of Fish-Face & Other Freaky-Looking Fish]

Until recently, scientists assumed the common ancestor of gnathostomes was more similar to cartilaginous fish. This ancestor "would have looked something like a shark, devoid of armor and with a largely cartilaginous skull," said study leader Min Zhu, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology, in Beijing.