The sensitive interior of human teeth may have originated from a seemingly unlikely place: sensory fabric in fish that swam in the earth oceans 465 million years ago. The scientists reported the findings on Wednesday (21) in the journal Nature.
Although our teeth are covered with hard enamel, it is dentin – the inner layer of the tooth responsible for carrying sensory information to the nerves – which reacts to the pressure of a strong bite, pain or changes such as extreme cold or sweetness.
In trying to determine the origins of the teeth, one of the many possibilities considered by researchers over the years that teeth could have evolved from protruding in the armored exoskeletons of ancient fish. But the true purpose of these structures, called dentis, was uncertain.
Now, a new study And fossil 3D scanning provided evidence that these external protuberances contained dentin, which probably helped the fish to perceive their surroundings.
“Covered by these sensitive tissues, perhaps, when they bumped into something, they could feel this pressure, or perhaps they could realize when the water was very cold and needed to swim somewhere else,” says the main author of the study, Yara Haridy, a postdoctoral researcher at the Department of Biology and Organisms of Chicago, in an email.
During their analysis, the team also discovered similarities between the odontoans and sensitive structures, which exist as sensory organs in the carapaces of modern animals such as crabs and shrimps, and can be found in fossilized invertebrate arthropods. The development of fish in fish, which are vertebrates, and sensils in arthropods, which are invertebrates, is a classic example of evolutionary convergence – when similar characteristics evolve independently in different animal groups, according to Haridy.
“These fish without jaw and aglaspid arthropods (extinct marine arthropods) have an extremely distant common ancestor that probably had no hard part,” says Haridy. “We know that vertebrates and arthropods have evolved hard parts independently and, surprisingly, they have developed similar sensory mechanisms integrated into their hard skeletons independently.”
While the arthropods maintained their sensilas, the odontes seem to be the direct precursors of the teeth in the animals.
By comparing sensilas and dentis, the researchers also reached another discovery: one species, once considered an old fish, was actually an arthropod.
The search for older vertebrates
Haridy’s initial goal was to solve the oldest vertebrate mystery in the fossil record. She sought museums from all over the country and asked if she could scan any fossil specimens they had from the Cambrian period, which occurred between 540 million and 485 million years ago.
She then prepared for an entire night at the Argonne National Laboratory, where she used Advanced Photon Source to capture high -resolution computerized toseography (CT).
“It was a night on the particle accelerator; it was fun,” says Haridy.
At first glance, a fossil of a creature called Anatolepis it seemed to be a vertebrate fish – and in fact, previous 1996 research had identified it as such. Haridy and his colleagues noticed that there were a series of pores filled with a material that seemed to be dentin.
“We were greeted, like ‘my God, we finally got it,” says Haridy. “That would have been the first structure similar to a tooth on Cambrian vertebrate tissues. So we were very excited when we saw the characteristic signs of what seemed to be dentin.”
To confirm the discovery, the team compared the scan with those of other ancient fossils, as well as with modern crabs, snails, beetles, sharks, barnaches and even small pens that Haridy herself had created.
These comparisons showed that Anatoolepis resembled arthropod fossils, including one of the Milwaukee Public Museum. And what the team thought were dentin -lined tubules were actually more sensitive to.
But they actually found dentis containing dentin in old fish like ERIPTYCHIUS and Astraspis during scanning.
The confusion about the true nature of Anatolepis arose from the fragmentary nature of fossils. The most complete pieces are only about 3 millimeters (0.1 inch) in size, according to Haridy, which proved to be a challenge for comparative research based on external images.
But the new scan she performed allowed a 3D visualization of fossils, revealing her internal anatomy.
“This shows us that ‘teeth’ can also be sensory, even when they are not in the mouth,” says Haridy. “Therefore, there is sensitive armor in these fish. There is a sensible armor in these arthropods. This explains the confusion with these initial Cambrian animals. People thought it was the oldest vertebrate, but it was actually an arthropod.”
The modern state-of-the-art technology used in the study is solving the debate about AnatoLis, according to Richard Dearden, a postdoctoral researcher at the Naturalis Biodiversity Center in Leiden, the Netherlands. Dearden did not participate in the new research.
“The authors use modern cutting -edge image approaches to try to solve this issue, gathering an impressive set of comparative data to establish convincingly that Anatolepis It’s not really a vertebrate, ”says Dearden in an email.
Armor against the elements
Armored fish without jaw as Astraspis and ERIPTYCHIUS and ancient arthropods like Anatolepis coexisted in the shallow and muddy seas of the period Ordovicianwhich occurred between 485.4 million and 443.8 million years ago.
Other contemporaries of these animals included large cephalopods, such as giant squids, as well as huge marine scorpions. Characteristics such as odontoids and sensilas would help fish and arthropods to distinguish prey predators.
“When you think of a primitive animal like this, swimming out there with armor, it needs to realize the world. It was a very intense environment in terms of predators, and being able to realize the properties of water around it would have been very important,” says senior study author Neil Shubin, Professor Robert R. Biology and organism anatomy at Chicago University, in a statement. “So here we see that invertebrates with armor, such as the corner crabs, also need to perceive the world, and by chance, they have reached the same solution.”
Several modern fish have dentis, while sharks, rays and some catfish are covered with small denticles, which make your skin look sandpaper, according to Haridy.
Haridy studied the tissues of the Cascudos he created and realized that his denticles were connected to nerves in the same way as the teeth in the animals. When comparing teeth, dentis and sensilas, they were all incredibly similar.
“We believe that the first vertebrates, these big armored fish, had very similar structures, at least morphologically. They look the same in old and modern arthropods, because they are all forming this mineralized layer that covers their soft tissues and helps them perceive the environment,” says Haridy.
It is likely that the genes needed to form dentists have also produced sensitive teeth in animals – including humans – later, according to the authors of the study.
The findings support the idea that sensory structures first emerged in exoskeletons, which then provided the genetic information that could later be used to create teeth as they became a necessary part of life, the study authors observed.
“Over time, the fish evolved jaws, and it was advantageous to have pointed structures around and inside the mouth,” says Haridy. “Little by little, some fish with jaws had pointed dentis on the edge of the mouth and eventually some were directly inside the mouth and disappeared from the rest of the body. The relationship between dentis and teeth is being continually clarified by new fossils and modern genetics.”
The new research refines the timeline for the first appearance of hard tissues and the oldest ancestors of fish with jaw when removing Anatolepis From the Tree of Life of Pisces, according to Lauren Sallan, assistant professor and head of the Okinawa Institute of Science and Technology Macroevolution Unit in Japan. Sallan, who did not participate in the new study, says that this also raises a new intriguing hypothesis: that the forecasts in the form of teeth scales have evolved to detect prey, partners or water predators.
“This is a real challenge for seemingly obvious assumptions that hard tissues such as dentin and structures such as scales and teeth have evolved (mainly) for body protection or diet in the mouth,” says Sallan. “Instead, they may have been ‘exhausted’ (later modified) for these uses, just as the members evolved before they are used to walk on land. It is also interesting to see the degree of convergence between the first armored arthropods and fish, and raises questions about how much ecological overlap existed between these two groups.”
Haridy wants to continue the search for fossils that can lead to the older vertebrate, as researchers believe there are vertebrates prior to Astraspis and ERIPTYCHIUS. And although they did not discover this in this research, they made valuable discoveries, says Shubin in an email.
“We were disappointed by Anatolepis Not being a vertebrate, but we marvel at the new ideas that came up, ”says Shubin.“ And that led us to a totally new direction. This is science. ”
This content was originally published in human teeth may originate from sensory structures of old fish on the CNN Brazil website.
Source: CNN Brasil
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