Scientists have discovered an ancient predator fish which lived in tropical waters some 423 million years ago that presents important clues about the evolution of the jaw.

This armored fish dwells at the muddy bottom of the ocean was found in the Yunnan province in China. Fossils of the Qilinyu rostrata, which measure about 12 inches long, have some bones that can also be seen in modern day vertebrate jaws and also in humans.

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This primordial specimen belongs to the placoderms, which is an already extinct group of fish covered in bony scales that appear like armor. This scaly armor covered the head and most of its body of the fish. It also had distinct jaws and bony plates that may have served as teeth to tear through the flesh of its prey.

This new fossil find is crucial since it presents evidence of the first fish that possessed jaws, as the planet's first vertebrates were jawless, only having suction type mouths around half a billion years ago.

 Placoderms are the first group of fish that possessed mouth and scale structures similar to jaws, which enabled them to latch on and catch prey without any teeth.

More specifically, the Qilinyu had three types of bones known as the maxilla, dentary, and the premaxilla that all characterize modern jaws in fish, mammals, reptiles, amphibians, except for sharks.

The maxilla and the premaxilla are bones found in the upper jaw while the dentary is a bone found in the lower jaw.

According to paleontologist Per Ahlberg from the University of Uppsala in Sweden, this jaw appears to evolve from these bony plates of placoderms, before teeth came to be in fish.

This new study was published in the journal Science.