According to a new X-ray analysis of a fossil, human teeth in a bizarre shellfish “developed 400 million years ago”.
Paleontologists have used the European Synchrotron Radiation Facility (ESRF), the most powerful X-ray source in the world, to “digitally dissect” the primitive jawfish.
The teeth of the extinct Akanthothoracid fish were discovered near Prague in the Czech Republic almost 100 years ago.
However, they are trapped in the cladding of rock and scientists have never been able to examine them before.
However, the non-destructive X-rays revealed hidden details of their size and structure and showed a remarkable resemblance to human teeth.
Humans and all 60,000 living species of vertebrates ̵
Artist’s impression of a tropical reef in the Czech Republic 409 million years ago with acanthothoric acid, one of the most primitive jaw vertebrates with teeth. It is shown emerging from its hiding place in the empty shell of a giant mollusk in search of food
“These results change our overall understanding of the origin of teeth,” said study co-author Professor Per Ahlberg, a paleontologist at Uppsala University in Sweden who led the research.
“Their jawbones are similar to those of bone fish and seem to be descended from our ancestors.
“If you grin in the bathroom mirror in the morning, the teeth you grin on can trace their origins back to the first vertebrates with jaws.”
The teeth of current vertebrates with jaws, including humans and sharks, have some consistent patterns.
For example, new teeth usually develop on the inside of the old ones and then move outwards to replace them.
In humans, this pattern has been modified so that new teeth develop under the old ones deep in the jawbone.
During the experiments at the ESRF, the European Synchrotron: Members of the research team assembled a sample in the test house of the ESRF ID19 beamline
However, there are several differences between bony fish – and their offspring, including humans and other land animals – and sharks.
For example, sharks have no bones at all and a cartilage skeleton, and their teeth just sit in the skin.
In bony fish and land animals, the teeth are always attached to jaw bones.
Trying to understand how all these different species have similar teeth has long been a mystery, and the researchers had focused on fossils from a group of old fish that lived around 430 to 360 million years ago and were called arthrodes.
This extinct order of fish is called the stem species, a common ancestor of many different offspring. It was believed that they were the first vertebrate with jaws to have teeth.
However, paleontologists have had difficulty understanding how they could have developed into the teeth of modern vertebrates, because the differences between bony fish and sharks are so great.
The European research team, which included staff from the Natural History Museum in London, therefore set out to determine whether Arthrodire was our ancestor or just a specialized branch of the line.
ESRF: “THE BIGGEST X-RAY IN THE WORLD”
The European Synchrotron Radiation Facility (ESRF) is the most intense source of synchrotron light, producing X-rays that are 100 billion times brighter than X-rays used in hospitals.
These X-rays are generated by the high-energy electrons that race around a circular tunnel that is half a mile in circumference.
ESRF works like a “super microscope” that “films” the position and movement of atoms in condensed and living matter.
This shows the structure of matter and new knowledge for scientists in the fields of chemistry, material physics, archeology, nanotechnology and more.
They turned to the Akanthothoracids, another early group of fish that was considered more primitive than the Arthrodire and was closely related to the very first vertebrates with jaws.
The problem with acanthothoracids is that their fossils are rare and always incomplete.
The very best Akanthothoracid specimens come from the Prague Basin in the Czech Republic, from rocks that are just over 400 million years old and were collected around the turn of the century.
It has proven difficult to examine them using conventional techniques because the bones cannot be cleared of the surrounding rock and have therefore never been examined in detail.
The team therefore turned to the unique properties of the ESRF to visualize the internal structure of the fossils in 3D without damaging them.
At the ESRF, an 844-meter-long electron ring that moves at the speed of light emits powerful X-rays that can be used to non-destructively scan matter, including fossils.
“The results were truly remarkable, including well-preserved bits that nobody expected to be there,” said lead study author Valéria Vaškaninová from Uppsala University.
Follow-up scans with higher resolution helped to visualize the growth pattern and even the perfectly preserved cell spaces in the dentin of the teeth – the layer of material that lies beneath the enamel.
Like Arthrodire, the Akanthothoracid bits are attached to bones.
Sharks are now specialized in having teeth that only stick to the skin – contrary to the general belief that sharks are primitive living vertebrates.
The European Synchrotron Radiation Facility (ESRF), a joint research facility in Grenoble, France
In other ways, Akanthothoracid dentures differ fundamentally from those of arthrodiruses.
Like sharks, bony fish and land animals, acanthothoric acids only added new teeth to the inside of the old ones, while the oldest teeth were right on the edge of the jaw.
In this regard, the Akanthothoric Acids look remarkably modern.
“To our surprise, the teeth perfectly matched our expectations of a common ancestor dentition for cartilaginous and bony vertebrates,” said Vaškaninová.
The tooth-bearing bones also carry small, non-biting dentin elements of the skin on their outer surfaces – a property that is common to primitive bone fish, but not arthrodiruses.
This is an important difference, as it shows that Akanthothoracid jawbones were right on the edge of the mouth, while Arthrodire jawbones were further inside.
The results were published in the journal Science today.