History Of Jaws Associated With Ancient Armored Fish

The discovery of a 423-million-year-old armored fish from China indicates that all modern land vertebrates and bony fish get their jaws from it. The armored fish has a head like a dolphin and the body appears to be a tank. The jaws originated in a peculiar group of animals called placoderms.

Paleontologist John Maisey of the American Museum of Natural History in New York City says that Qilinyu rostrata, a new finding along with the different placoderm fossil discovered in 2013 is helping researchers rewrite the story of the evolution of early vertebrates. Maisey was not involved in the study.

The maxilla and premaxilla of upper jaw and the dentary of lower jaw are the three major bones present in the jaws of humans, salmon, dogs, lizards and other vertebrates, according to Science News. "Anything from a human being to a cod has recognizably the same set of bones in the head," states study co-author Per Ahlberg, a paleontologist at Uppsala University in Sweden. The big question, he says, is "Where did these bony jaws come from?"

Scientists had evidence about the presence of fishes called placoderms under water a hundred million years before the dinosaurs lived on the surface of Earth. They were aware that these armored fishes were the earliest jaw animals, but their jaws were strange. "They look like sheet metal cutters," Ahlberg says. "They're these horrible bony blades that slice together."

The gnathal plates, as the blades are called, looked so bizarre that mmost researchers thought that placoderms were only a strange branch in the vertebrate family. They believed that the 3-part human jaws originated in an early bony fish. Paleontologist Martin Brazeau says that placoderms are one of the most debatable groups of animals. No one is quite sure where to place them.

In 2013, Ahlberg and his colleagues had discovered the 419-million-year old fossil that had the body of a placoderm but the jaws were similar to that of a bony fish. Such an animal could have never been predicted from any of the fossil records.

Ahlberg believes that the two fossils form almost perfect intermediates between bony fish and placoderms. He says this is part of early human evolutionary history. It shows where the human jaws came from.