The discovery of an Entelognathus fish fossil along with the Qilinyu remains revealed that the evolution of human jaws has a complex origin and it can be traced to both ancient fish.

The Entelognathus is the most primitive vertebrate to have modern jaws including maxilla, premaxilla, and dentary. The Qilinyu also have the same jaw structure, which is found in bony fish, reptiles, and mammals, including humans.T he Qilinyu is believed to have swum the Earth 423 million years ago, and it is linked to human’s jaw formation. 

Min Zhu, from the Chinese Academy of Sciences, shows a fossil of the armored fish, Entelognathus, in front of a computerized rendition of how the fish might have appeared when it lived about 419 million years ago. Photo by Kim Kyung-Hoon/Reuters/Corbis

Scientists from China’s Yunnan province said on Tuesday that the Qilinyu, a placoderm, has the telltale bones presents in modern vertebrate jaws, including people.

Placoderms are prehistoric fish covered in bony armors that protected their heads and part of their body. Placoderms are also characterized by boasting jaws armed with bony plates that acted as teeth to allow fish like the Qilinyu to slice its prey.

Placoderms were the first vertebrates with jaws. Fish have been on Earth more than half a billion years ago, and at first, they did not have jaws, only a mouth design to suck prey. But an evolutionary process modified their mouth to have jaws and allowed them to catch their prey, and eventually, they develop teeth to tear the flesh apart.

Scientists have studied placoderms for years, but also, as an evolutionary dead-end when it comes to tracking the origins of the human jaw, until the discovery of the Qilinyu and the other placoderm fish: The Entelognathus.

Both fossils have the three elements that compose the modern jaw: maxilla, premaxilla, and dentary. The findings fill the blank in the evolutionary process of humans jaw and linked people to prehistoric evolution. The maxilla and premaxilla are bones of the upper jaw, and the dentary refers to the bone of the lower jaw.

The study was published October 20 in the journal Science by paleontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) along with Chinese Academy of Sciences and Uppsala University in Sweden. The research includes comparisons between the Entelognathus fossil, which was found first, and the Qilinyu fossil.

“Qilinyu expands our understanding of maxillae placoderms, previously represented only by Entelognathus. Qilinyu has a different body shape, with a ventrally positioned mouth and nostrils that are suggestive of a benthic feeder,” said  Professor Zhu Min of the IVPP the study leader and project designer, also a professor at the Chinese Academy of Sciences University.

The head of Entelognathus. Image Credit: John Long

Qilinyu: Contradicting past theories about jaw evolution

The recent study contradicts previous notions that say that modern jaws architecture evolved later in history from bony fish and not from placoderms. At first, the Entelognathus fossil, which was found in 2013 in China, was not considered a placoderm fish. But after the Qilinyu was located by the Kuanti Formation of Qujing in Yunnan, also in China, scientists could both fish to placoderms and human evolution.

Comparing both fish help scientists to conclude that human jaw bones patterns show old gnathal plates of placoderms, present in both the Entelognathus and the Qilinyu fossils.

Source: Chinese Academy of Science