Did you ever wonder where your jaws came from? A recent study conducted by palaeontologists from China and Sweden has revealed that our jaws can be traced back to extinct armoured prehistoric fish that has dominated the oceans and rivers around 400 million years ago. The findings, published in the US journal Science, were based on a newly discovered fossil fish in Yunnan known as Qilinyu, which is part of the ancient armoured fish. The discovery of the 423-million-year-old fish fossil “fills a big gap in our understanding of how vertebrate jaws evolved”, John Long, a palaeontologist at Australia’s Flinders University, wrote in an accompanying article in the journal. The question of where our jaws came from is “more complicated than it seems, because not all jaws are the same,” Zhu Min of the Chinese Academy of Sciences said in an email on Friday. All modern vertebrates, including us, have a jaw that is composed of three parts: the dentary, maxilla and premaxilla. But further back in time, only one other group of fishes, the extinct placoderms, have a similar set of jaw bones. These bones, known as “gnathal plates”, have always been regarded as unrelated to our jaw. The picture began to change in 2013 when Zhu and his colleagues unveiled a fossil, called Entelognathus, that had a placoderm-like body but a three-part jaw in Yunnan. However, there was some uncertainty as to whether those jaws came from. Now, Zhu and Per Ahlberg from the Uppsala University in Sweden reported the discovery of Qilinyu that came from the same place and time period as Entelognathus, The preserved part of the fossil is 126mm in length, with an estimated total body length of more than 20cm. With a dolphin-shaped head, this fish appears to have dwelled and fed along the bottom of bodies of water. The simplest interpretation of the observed pattern, according to the researchers, is that our own jaw bones evolved from these old gnathal plates of placoderms.