|Illustration of Entelognathus primordialis, a primitive extinct fish from 419 million years ago and the earliest known creature with jawbones presumed to be the prototype for human facial architecture. Credit: Brian Choo
New Delhi, Sept. 25: The fossil of a primitive fish from 419 million years ago discovered in limestone sediments on a hillside in southern China has been identified by scientists as the earliest known creature with what humans would recognise as a face.
A team of Chinese and Swedish palaeontologists said today the bones that made up the cheek and jaws of the extinct fish are essentially similar to the bones found in modern bony vertebrates, including humans. The 11-member team has described the fish — Entelognathus primordialis — in today’s issue of the international journal Nature.
The fossil, which some palaeontologists have described as “remarkable”, is likely to make researchers rethink existing ideas about how present-day jawed vertebrates acquired these characteristic facial features.
“This fossil shows the earliest prototype of our own facial architecture,” Per Erik Ahlberg, a palaeontologist and a team member at Uppsala University in Sweden, told The Telegraph.
The Entelognathus, Ahlberg said, is the most primitive and one of the earliest vertebrates with premaxilla, maxilla and dentary, the three key bones that are also found in the modern human jaw.
Scientists believe the earliest vertebrates and their surviving relatives such as lampreys or hagfish had no jaws — they had round holes for mouths, at times girdled by tentacles as seen in present-day hagfish.
The Chinese-Swedish team has classified the Entelognathus as a placoderm, an extinct family of primitive armoured fish. Until now, all placoderms had been thought to have far simpler jaws made up of largely cartilage with the outer surfaces made up of a few large bones.
But Entelognathus had a more complex arrangement of smaller bones — a premaxilla and maxilla lining the upper jaw, and a dentary or the lower jaw and cheekbones.
“The bones that make up the cheek and the jaws of Entelognathus are essentially the same ones found in modern bony vertebrates, including humans,” Min Zhu, a Beijing-based scientist at the Institute of Vertebrate Paleontology and Paleoanthropology who led the research study, told this newspaper.
The lower human jaw is called the dentary and the human upper jaw is made up of the premaxilla that supports the front teeth and the maxilla that carries the canine and cheek teeth. “In Entelognathus, we see these three bones for the first time in placoderms,” Zhu said.
Such primitive jawbones had been previously restricted to bony fish and the tetrapods, the super family of four-limbed vertebrates including living and extinct amphibians, reptiles, birds and mammals.
The fossil recovered from a hillside in what Ahlberg calls “classic Chinese farming country” marked by villages and terraced fields, shows that the jawbones have a deeper, older origin than previously suspected. But the fossil record from that era is so incomplete that it is difficult to say how much older.
“The fauna that Entelognathus comes from is one of the earliest that yields jawed vertebrates, but it also contains a more advanced form, the early bony fish called Guiyu,” Ahlberg said.
“Because of its primitive characteristics, we can tell Entelognathus represents a lineage that goes back further in time than bony fish,” he said. “But how much further? We can’t say, though we’re certainly talking about millions — maybe tens of millions — of years.”
Two palaeontologists who were not associated with the finding said the Entelognathus fossil “demands a major rethink of where fossils fit relative to modern lineages and how these living groups came to acquire their characteristic traits”.
In a commentary in the same issue of Nature, Matt Friedman from Oxford University and Martin Brazeau from the Imperial College, London, wrote that the discovery of this “remarkable fossil” has stirred a “major reframing” of ideas about the evolution of jaws.