Humans owe the origins of their teeth to extinct fish that roamed the oceans 400 million years ago: Study

The prehistoric organism is named acanthothoracid, a type of armored fish, which gets its name from its appearance: heavy armor wrapping the creature's head and neck


                            Humans owe the origins of their teeth to extinct fish that roamed the oceans 400 million years ago: Study
(Jan Sovak)

There is a part of a fish that roamed the oceans about 400 million years ago within us. Humans and 60,000 species of jawed vertebrates -- sharks, bony fish, amphibians, reptiles, birds, and mammals that inhabit the Earth today -- owe the origins of their teeth to this extinct fish, according to a new study. The prehistoric organism is named acanthothoracid. It is a type of armored fish, which gets its name from its appearance: heavy armor wrapping the creature's head and neck. It is not usual that our teeth have their origins in ancient fish as we descended from the extinct marine species.

The oldest fish that lived in the early period has no jaws. This population was covered with bony armor plates carrying tooth-like-features. The structure from the skin may have invaded the mouth, later on, to become teeth. "But what were the earliest true teeth like? This is where the evidence from our acanthothoracids comes in", Per Ahlberg, co-author, and professor at Uppsala University, told MEA WorldWide (MEAWW). 

Previous studies have traced the origins of human teeth to another extinct armored fish called Arthrodira that lived about 430 to 360 million years ago. But Per Ahlberg and his colleagues were not convinced. "The arthrodire teeth are really weird," he explained, adding that the arrangement does not resemble modern ones.

So the team examined fossils of a more ancient armored fish: acanthothoracid. They are present in the Prague Basin in the Czech Republic -- home to some of the well-preserved specimens."They have been famous for almost a century. But they are notoriously difficult to study because the rock cannot safely be removed from the bone."

Researches examining a specimen (Boris Ekrt)

Conventional fossil-analyzing techniques proved futile. That led the team to turn to a sophisticated X-ray scanner that allowed them to visualize the internal structure of the fossils in three-dimensions, without damaging them. The researchers hoped that the scan could reveal the secrets of the origin of vertebrate teeth.

"One of the first things we saw in the scan images was teeth buried in the rock!" Ahlberg said, calling it a crucial discovery because researchers have found almost no teeth of acanthothoracids until then, barring a single pair of tooth plates in a Canadian specimen, he added. The team then scanned the Prague fossil again --this time, they targeted the teeth. "To our surprise, the teeth arrangement in acanthothoracid perfectly matched our expectations of a common ancestor for modern vertebrates," Valéria Vaškaninová, lead author of the study and scientist from Uppsala University, explained.

Modern jawed vertebrates are of two types. One, the cartilaginous group, which includes sharks and rays, while bony fishes and land vertebrates belong to the second. As per Ahlberg, both groups have some similarities, including their teeth arrangement and shedding. But they have differences too. Sharks lack bones, and so, their teeth sit on the skin, while others have it attached to the bone. 

The analysis showed that common ancestor of the two groups, the acanthothoracids, also have teeth that are attached to bones but they do not shed. "It looks like tooth shedding was invented independently by sharks and by bony fish and land vertebrates," Ahlberg explained. The limitation of the study includes the fact that the team had access to fossils and not the whole anatomy with the soft tissues. As a result, the researches are not sure of the exact appearance of the entire arrangement.

The study is published in the journal Science.

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