Fish face: The oldest face in history.
What do our smiles and that of an extinct ancestor of fish have in common? Much more than one might imagine at first glance. A fossil of an aquatic animal found in China traces back to the origin of the chewing apparatus in vertebrates.
By: Oasis Team
Take a good look at the illustrative image that opens this article. Then, look at yourself in the mirror. Isn't there a certain resemblance? For evolutionary biologists, we humans and Entelognathus primordialis – a primitive fish that lived during the Paleozoic era – share a fundamental somatic characteristic: the shape of the jaw.
This aquatic creature lived in an area near present-day China between 450 and 415 million years ago. It is the oldest animal to possess a mouth apparatus similar to that of modern vertebrates, including humans.
He has the same mouth as us.
A perfectly preserved fossil of this proto-fish, dating back 419 million years, was described by paleontologist Min Zhu, a member of the Institute of Vertebrate Paleontology and Paleoanthropology, part of the Chinese Academy of Sciences in Beijing, in an article published in the journal Nature.
The fossil exhibits the characteristic three-element skeletal system still used by vertebrates for chewing: a lower jawbone (the mandible) on which the dental arch rests, and two upper bones: the premaxilla, in which the incisor teeth are inserted, and the maxilla, which contains the canine teeth and molars. In mammals (including humans), the two upper bones are fused.
The arrangement of these bones is substantially the same as in modern vertebrates: that of Entelognathus would therefore be the first "face" with the characteristics we are accustomed to associating with it. The development of a powerful jaw represented a fundamental step in the evolution of vertebrates. The first bony fish probably developed it to better capture larger and faster prey.
A complicated family tree
When there was only one continent on Earth
Entelognathus primordialis may have been an atypical member of the placoderm class, ancestors of fish that roamed the oceans between 430 and 360 million years ago, when Earth still consisted of a single continent called Gondwana. These animals, characterized by a true bony armor around their head and thorax, possessed a primitive jaw structure composed of a few large bony plates (and not a complex structure of smaller bones as is the case with modern bony fish).
Cartilaginous fish (like sharks) and other fish with bony skeletons originated from placoderms. Until now, it was believed that the facial features of placoderms had been lost during evolution, and that the last common ancestor of today's vertebrates was more similar to a primitive shark, with a cartilaginous skeleton covered, at most, by small bony plates.
The fossil found in China, however, is a kind of hybrid that combines many characteristics of placoderms (such as the armored body, which sharks do not possess) and also some somatic traits of modern vertebrates, such as the existence of a jaw. The origin of the shape of our face will therefore have to be traced back in time, to the era of this prehistoric animal possessing a giant jaw.