Do you think teeth are dull or boring? From the iron-filled teeth of Komodo dragons to the horns of sea unicorns, the animal kingdom is full of amazing dental adaptations that will make you think again.
Sharks are covered in tooth-like scales called denticles
Color micrograph of shark skin showing the complex three-dimensional structures of its denticles.
Gregory S. Paulson/Getty Images
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Cartilaginous fish such as sharks, rays, skates, and chimaeras grow three-dimensional scales on the surface of their skin. Each tooth-like scale has a pulp cavity containing blood vessels and nerves and is covered with a mineralized enamel-like tissue. These scales—unlike the flat, saucer-shaped scales of bony fishes—are called denticles and vary widely in shape and characteristics, not only between species, but also within a fish. The denticles found on a shark’s nose can be flat and round, resembling the patchy surface of a soccer ball. But elsewhere on the body, the denticles could look like overlapping knobby hands with ridges and dots.
These denticles can serve a variety of functions, such as reducing drag in swimming and possibly increasing direct propulsion, explains Purdue University biomechanist Dylan Wainwright. “We think they also act as a buffer to the sharks in some way,” Wainwright continues. “They can protect them from other big things like bites from other sharks (and) small things like ectoparasites.” (Some fish have been observed rubbing the rough skin of the sharks to get rid of their parasitic knights.)
We still don’t know where teeth come from
Two competing theories of the evolutionary origin of teeth have been battling for decades, aided by recent discoveries in developmental biology or the fossil record. The “outside-in” hypothesis suggests that tooth-like dermal scales with hard mineral-covered pulp centers—similar to the denticles found today—gradually migrated along the outer surface of the body over generations of fish before moving inward to inhabit the jaws of our ancestors. . The “inside-out” hypothesis suggests that teeth originated internally before migrating into oral teeth in the oral cavity.
An research the rostral denticles (the “teeth” of the fish’s sawbill) of a fossilized sawtooth shark showed complex internal structures remarkably similar to those found in shark teeth. This finding suggests that the developmental difference between dermal scales and teeth is smaller than previously thought, once again displacing the outside-in-outside hypothesis. Given the inherently spotty nature of the fossil record, however, it’s entirely possible that we’ll never know exactly where our oral teeth came from.
Some species of fish have not one, not two, but three types of teeth
Most fish have two sets of teeth: oral teeth near the front of the mouth for grabbing and cutting, and pharyngeal teeth located in the throat for slicing and slicing. But some fish, in a group known as osteoglossomorphs, have also developed a third set of teeth: the bony plates that form the roof of the mouth and the tongue (“osteo” means “bony”; “glossi” means “tongue”). . help them crush and mince their food. “Fish seem to put their teeth wherever they want,” says Kory Evans, a fish biologist at Rice University, “and fish can continue to make teeth throughout their lives, which is really impressive.”
The most abundant vertebrate fossils on the planet are microfossil fish teeth
As fish replace their regular teeth, the shed teeth will fall to the bottom of the water column and become embedded in the sediment. Unlike more porous bone, these hardened teeth are less susceptible to wear and tear and degradation. Considering that fish have been around for 530 million years or more, it should come as no surprise that sediments around the world are full of fossilized fish teeth. But good luck seeing them in the wild. “They’re smaller than a human hair, but these tiny, tiny, tiny fish teeth can tell powerful stories,” says Elizabeth Sibert, an oceanographer and paleobiologist at Woods Hole Oceanographic Institution.
Like microscopic ice cream cones, these microteeth vary in thickness, length, curvature, presence or absence of spines, etc. Based on the relative abundance of these teeth over time and the geographic distribution of the different shapes, Sibert and his collaborators can make inferences about animal diversity, animal abundance, and food webs in ancient oceans. And how many of these microfossil teeth might be out there? “Definitely billions,” believes Sibert, “and I think trillions might not be that far off.”
Parrotfish beaks, built from compressed teeth, contain the stiffest biomineral ever discovered
Parrotfish (Chlorurus gibbus) with an impressive beak.
Ute Niemann/Alamy Stock Photo
Most parrotfish species eat corals for polyps and algae (they help white sand), but biting coral is not an easy thing. Parrotfish beaks are made of the hardest biological mineral ever discovered, replacing limpet (snail) teeth, which held the previous record.
Parrotfish beaks are formed by 1,000 compressed teeth arranged in 15 rows in a hard, conglomerate structure covered with a layer of enamel. Esameloid crystals are woven like tissue, but on a scale of two to five microns (smaller than a red blood cell). This woven structure gives one square inch of parrotfish beak the ability to withstand the force equivalent to the weight of 88 elephants.
The transparent teeth of deep-sea fish can provide camouflage
In the mouth of this deep-sea angler fish you can see striking transparent (Melanocoetus sp.) female
Nature Picture Library/Alamy Stock Photo
Deep sea fish will never win a beauty contest, but they can survive hundreds of meters below, if not more several kilometers awayThe water is not easy, and these fish are full of incredibly strange arrangements that should win them some awards. The long, slender, transparent teeth of anglefish, dragonfish, and the like are fascinating in more ways than one. First, although the long fingers may look sharp, these teeth are not designed to dig, but to grab! Many deep-sea fish species have “depressed” teeth that bend only inward and function like a one-way valve. Food can go in, but not out. Also, research suggests that a dragonfish’s smile doesn’t exactly light up a room. Any ambient light (like that created by bright booty) passes through tooth structure instead of bouncing off a dense surface and reflecting outward, as it would from our pearly whites. This allows deep-sea nightmares to approach their prey without their exposed teeth taking the game away.
Snake strikes evolved many times, but they all look the same
Although most reptiles do not strike and have no venom, many different species of snakes have developed mechanisms to deliver venom through their teeth. Snakes exhibit two main types of venom-delivering fingers: grooved, in which the venom travels down a posterior channel, and tubular, in which the venom flows through a closed wall tube. Tube colors have evolved in three separate snake families (vipers, cobras, and asps). In a class of animals where strikes are not very common, how is it that hatchlings have evolved more than once in different snake families and converged on roughly the same structures each time?
The answer seems to have a root. Many reptilian teeth have a pattern of zigzag indentations called plicidentines around the base where they attach to the jaw. The scientists hypothesize that one of the zags eventually developed into a long canal running the length of the brood, which could then be completely encapsulated within the brood as a canal. The presence of plicidentin constitutes an evolutionary shortcut to venom delivery, making repeated evolution of this adaptation likely.
Nature evolved metal teeth long before man invented the saw
For some lucky creatures, “jaw of steel” isn’t too far from the truth. Some animals have developed iron-containing chompers to strengthen and protect their teeth. Beavers They are a prime example of mammals; their incisal enamel is rich in iron and able to withstand the repetitive growth and shearing of fibrous plant tissue. Researchers found this out recently Komodo dragon teeth they also have strategically placed iron on the serrated edges. This is particularly surprising because Komodo dragons, like most reptiles, replace their teeth frequently. The metabolic cost of investing in and growing thousands of iron-filled teeth over a lifetime has to be worth it.
Narwhal parts are grown canine teeth
narwhal (Monodon monoceros) across water surface tussocks off Baffin Island, Nanavut, Canada.
Nature Picture Library/Alamy Stock Photo
The distinguishing feature of the narwhal or “sea eel” is a long, spiral horn that protrudes from the animal’s forehead. But it is not a horn, but a tooth. Narwhals have two large teeth embedded horizontally in the skull, one of which (usually the left tooth, although sometimes the right or rarely both) protrudes from the skull in what we think of as a branch to continue growing. And even more strangely, these prongs always curl counter-clockwise, although in the odd case a narwhal has two prongs. This may be the mechanism by which narwhals’ tusks grow straight, compared to the curved tusks of elephants and wild boars and the large, curved canines of walruses and hippopotamuses. Also, the fingers are not covered with enamel, as most teeth are, but with cementum, which is a more flexible mineral coating. Given that most narwhal whales are bred by males, it is not surprising that they have been shown to play a role. sexual selection.
Plaque-causing bacteria and fungi can travel along the surface of our teeth
We have long known that bacteria living on human teeth can cause surface damage leading to plaque build-up and tooth decay. But scientists did some amazing discoveries Recently, this can provide motivation to brush and floss a little more regularly. Not only have fungi been found in saliva samples from children with severe diarrhea, they have also observed bacteria and fungi interacting under the microscope! These conglomerations are able to spread or “walk” across the surface of the teeth and combine with other Frankensteinian bacterial colonies to grow larger.
