The 419-million-year-old fish fossil could help explain when and how vertebrates, including humans, acquired our faces—suggesting a far more primitive origin for this critical feature of our success, a new study says.
"Entelognathus primordialis is one of the earliest, and certainly the most primitive, fossil fish that has the same jawbones as modern bony fishes and land vertebrates including ourselves," said study co-author Min Zhu of the Chinese Academy of Sciences in Beijing.
"The human jaw is quite directly connected to the jaw of this fish, and that's what makes it so interesting."
University of Oxford paleobiologist Matt Friedman, who wasn't involved in the research but penned a commentary for Nature, said the fossil boasts a jaw and face structure that's nothing like those in any other known members of Entelognathus's extinct family of primitive armored fishes, the placoderms. These creatures had simple jaws and cheeks composed of just a few large bones, Friedman explained, rather than complex arrangements of smaller bones like those found in modern bony fishes and people.
But in the new fossil, found in China's Silurian Sea, has a distinctive three-bone system still used by chewing vertebrates today: a lower jawbone called the dentary and two upper jaw bones called the premaxilla (holding the front teeth) and the maxilla (holding the canine and cheek teeth).
"The exciting thing about this fossil is that when you look at the top of it, it looks like a placoderm, but when you look at the side of the fish and the structure of the jaw, it doesn't look like any placoderm that we know of," Friedman said.
"This tends to suggest the exciting possibility that these jawbones evolved way deep down in the lineage, so these features we used to hold as being unique to bony fishes may not be so unique.”
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