Back to 3. In the oceans of the Devonian period 700 million years ago, a large group of strange ancient sea creatures swam freely in the shadows of coral thickets: probosciss fish, spiral ammonites... But perhaps the most surprising thing is the well-known creature, the shark. The spindle-shaped body of 1 to 2 meters long, with intricate arrangements of sharp teeth, is like a modern shark, and the ancient shark is also trembling.
Fossils and other evidence suggest that sharks have generally survived in a smallly changing evolutionary manner since they first appeared on Earth, which is enough to prove that sharks' body structure is very useful, and they can effectively grasp the direction of evolution and achieve long-term adaptability. A very precise recent study proves that some species of sharks, including their ancient ancestors, can change the condition of their teeth at any time to adapt to changes in food.
The most immediate and vivid impression of sharks by most people is its school bus-like body and intimidating bloody mouth—the shark's mouth full of sharp teeth has long chilled them before the hopeless underwater animals are bitten by them. In fact, the vast majority of sharks, whether it is a gray mackerel shark that can quickly bite a tuna,
Or do you like to hide around and sneak around with a surprise attack of the sand tiger shark,
None of their feeding behaviors are worth showing off. Marine cartilaginous fish tend to choose easy-to-catch prey when feeding, such as fragile starfish, crabs and sea urchins. Thus, the feeding habits of marine animals can be inferred from their teeth: triangular teeth are well suited for biting and tearing vigorously, shark teeth are of this type, so it can swallow food larger than its own head; teeth arranged like long nails are suitable for catching slippery fish; and smooth and tight teeth are suitable for grinding food.
The white-spotted bamboo shark that lives in the waters of the Indian Ocean and the Pacific Ocean,
They are small local indigenous sharks that can be found in many aquariums because they are easier to feed and breed. Marine biologist Claril A. D. Vega owns such a group of sharks, which are used to study sharks' hunting behavior and swimming skills.
One day, when the animal graduate student Romans was feeding, he did not feed the white-spotted bamboo shark a soft food like squid and fish as usual, but instead gave the shark some English crabs. To his surprise, the sharks not only flocked to them, as if they liked the small snacks that could be changed, but also spat out some crab shells from time to time. This surprised Romans a little, and he realized that the sharks did not swallow the crabs in a vacuum, as he had originally imagined, but instead crushed them and then ate them.
In nature, the white-spotted bamboo shark has a wide range of feeding habits, including a variety of small fish and marine invertebrates such as shrimp and crabs. Amazingly, the teeth of the white-spotted bamboo shark become a "generalist" when faced with different foods: sharp and small but perfect teeth can bite the prey in one bite and tear the prey into pieces with the help of the violent flick of the head. However, sharp teeth are more suitable for biting prey, so when the white-spotted bamboo shark bites some well-protected cloaked animals, how do they avoid teeth being impacted?
With the help of high-speed cameras and anatomical experiments, Romans finally cracked the secret of the teeth of the white-spotted bamboo shark - the flexible change of tooth angle. Shark lovers know that sharks generally have several rows of teeth, embedded in the ligament tissue of the shark's palate that is very elastic. These ligament tissues act like a conveyor belt that transports the back teeth to the front when they age and fall out. Usually, the frontmost tooth is responsible for biting and crushing the prey, when the rear teeth stay in place and do not get in the way until they are transported to the front row to perform their functions. In this way, the shark's teeth are constantly being renewed and replaced.
Romans also found that elastic gum ligaments ensure that the teeth of white-spotted bamboo sharks change direction to accommodate hard parts of their prey, such as the crust and bone. That is to say, the teeth of the white-spotted bamboo shark have a double effect: when encountering soft prey, the tip of the tooth stabs and firmly grasps the prey, and then tears the prey in half with the help of the violent swing of the head; and when encountering the hard prey, the tip of the tooth does not pierce into the prey, but instead, the tip of the tooth is folded into the mouth, so that the edge of the tooth touches the hard shell of the prey, just like a piece of metal resting on the hard surface, and the straight tooth surface is more suitable for the work of crushing the hard shell. Interestingly, this perfect system of white-spotted bamboo shark teeth does not require special control, and the hardness of the prey determines whether the teeth are bitten or crushed.
The teeth of the white-spotted bamboo shark are reminiscent of another of its ancient relatives, and this ancient shark, which can only be seen from fossils, also has a formidable pair of teeth.
Perhaps the perfection of teeth is the oldest and most common evolutionary strategy followed by sharks — the great white shark doesn't have teeth that can move and steer, but its static sharp teeth can also effortlessly bite off the surfboard, while the sand tiger shark bites through the hard turtle shell as easily as a chainsaw cutting a pine tree.