Sharks, the first thing that comes to mind when the word is mentioned is the cold-blooded killer in the ocean, and what comes to mind is the great white shark chasing the falling human with its blood basin open.
However, the shark, the creature that has been wronged for more than a hundred years, is not as terrible as people think.
Fear of sharks began in the summer of 1916. That summer, in the beaches of New Jersey, usa, in just 10 days, 4 people were killed and 1 was seriously injured. Since then, the image of "crazy man-eating great white shark" has gradually penetrated the hearts of the people. Coupled with Peter Benchley's 1974 book Jaws and Spielberg's film of the same name, the image of shark cruelty is basically solid.
However, the sharks are completely and utterly wronged.
The number of people who die in the mouth of sharks each year is single digits, while the number of people who die in the sting of bees can reach as many as 500 per year. The most heavily caught sledgehammer shark, in the nearly 400 years, has only killed one person in the news.
Contrary to the "common sense" of many people, sharks are far more afraid of humans than humans are afraid of sharks. This may stem from American resentment of sharks, which have declined by more than 80 percent in the last 25 years. This ancient creature that has existed for 450 million years, once the overlord of the seas, is now facing the most serious threat to life.
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This article will take you back to the past of ocean overlords
Travel back in time to a distant period of geological history
Meet a close relative of a shark
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Spiny tooth shark
New recovery of the spiny tooth shark (Source: National Geographic)
Helicoprion belongs to the genus Cartilaginous fishes - Plate gill subclass - Eugene tooth order - Spinodondae - Spiny tooth shark genus, "Helico" is derived from the Greek word "spiral", Prion is derived from "saw", named after the spiral arrangement of teeth.
The spinodon shark first appeared 290 million years ago (early Permian), survived the Permian-Triassic extinction event, and eventually became extinct 250 million years ago (early Triassic), with fossils distributed in North America, Eastern Europe, Asia and Australia.
Extrapolating from the spiral tooth disc up to 60 cm long, the individual body length of the spiny tooth shark can exceed 12 meters, and the body length range is 7.5-12 meters, which is the largest known Eugene tooth species and is a veritable sea giant.
Although the spiny tooth shark is called a shark, judging from the arrangement of the cartilage tissue at the site of the rock burial, it actually belongs to the whole-headed suborder, and is only closely related to the sharks belonging to the suborder Plate gill, and is only related to today's silverfish. It's just that in the past few decades people have often used spiny tooth sharks as sharks, and this misunderstanding has continued. In addition, the spiny tooth shark belongs to the same genus of spiny tooth sharks as many extinct fish such as scissor tooth sharks and para-spiny tooth sharks (Tailu sharks).
Spiral shark restoration (Troll, 2012)
Spiny tooth shark size comparison chart (Source: Zhihu)
Para-spinosaur size comparison chart
The spiny tooth shark has always maintained its most unique color among many ancient creatures, and where spiral teeth grow on the body is still debated. Cartilaginous fish have a characteristic, that is, the whole body bone is almost composed of cartilage (just like the bones of the ear), which means that the bones of sharks are difficult to retain as fossils, only the hard tissues such as teeth and scales can be preserved, so the natural world can hardly find the skeleton fossils of the spiny tooth shark, which adds a layer of mystery to the spiny tooth shark.
Now let's try to get closer to the world of the spiny tooth shark
Witness how this former sea monster was discovered
And how was it unveiled step by step
The discovery of the spiny tooth shark
As shown in the figure below, this is a strange biological fossil found by humans, a group of tooth fossils arranged in a spiral from large to small. The fossil was discovered in the Ural Mountains in 1899 by the Russian paleontologist Alexander P. Karpinsky. Originally, humans could only tell that this strange fossil was a strangely arranged set of teeth, and even where it should be was extremely controversial.
Fossil teeth of the spiny shark
Until 1907, such spiraling tooth fossils were also found in Iowa, USA, proving that these fossils are not simple cases. American paleontologist Oliver Perry Hay boldly guessed that this is a tooth belonging to a shark according to the similar characteristics of the tooth characteristics to the shark's teeth, at least in the question of attribution to a more accurate answer.
Recent photo of the teeth of the spiny shark
The controversy over the teeth of the spiny shark
Because the large number of early fossils of spiny sharks retain only teeth or spiral-shaped dental discs, there has been great controversy about the location of such strange teeth.
Andrzej P. Karpinski, the paleontologist who first discovered the spiny tooth shark, named it Helicoprion, made several attempts to restore the spiny tooth shark, initially trying to place the spiral tooth disc on the dorsal fin like a windmill, and also tried to put it on the tail or the tip of the nose, like an elderly person. Until 1952, russian paleoichthyologist Dimitri Obruchev believed that the position of the jaw "would only prevent fish from eating", and he put the roulette wheel on the palate, thinking that it could act as a shock absorber for the animal's head.
The first conjecture of the spiny tooth shark (Karpinski, 1911)
In 1995, Australian paleontologist John Long drew a hypothetical illustration in his book The Rise of Fish: The Evolution of Half a Billion Years, depicting the spiny-toothed shark's jaw curled downward into a spiral with dense teeth. He believed that the teeth of the spiny tooth shark could be rolled under the jaw, and when the prey approached, it could spit out its teeth as a whip, whipping the predatory animal and hooking the prey to the protruding teeth. He also believes that the spiny tooth shark rotates its jaw in order to imitate the appearance of ammonite (an extinct animal with shelled cephalopods and a favorite of the spiny tooth shark) in order to attract prey for prey purposes. This restored model was gradually recognized by most paleontologists, and until the discovery of the true spinosaur morphology, almost all the restorations were modified on this model.
On the issue of tooth growth, paleontologists have made two main points of view. One is that the roots of the teeth are closely connected during the growth process, and the newborn teeth will push the old teeth outward, just like nails, so the outermost teeth will be formed to form a phenomenon that the outermost teeth are small and the new teeth are large, which can prevent the teeth from falling out. Another view is that the size of the tooth is proportional to the jawbone that supports it, and the phenomenon of a spiral disc can only occur when the fish's body is long enough.
The face of the spiny tooth shark gradually became clear
Below is a summary of National Geographic's recovery of the spiny shark by different biologists since 1899, and a summary of the recovery of the spiny tooth shark in the Tapanila (2013) article. As can be seen from the figure, the initial position of the spiral teeth was arranged throughout the body, and after 1955, it was basically confirmed that they grew in the mouth, and then gradually discussed the shape of the teeth, and finally everyone's views gradually became consistent.
Restoration of the spiny tooth shark written by different paleontologists
(Source: National Geographic)
Summary of the recovery of the spiny tooth shark since 1899 (Tapanila, 2013)
The answer closest to the truth comes from more advanced research work in recent years.
Ramsay (2014) found a CT scan of the spiny tooth fossils stored in the Natural History Museum of Idaho, which retained traces of upper and lower jaw cartilage, and according to the reduction work of the CT scan, it can be clearly seen that the spinosaur tooth fossils are wrapped in the lower jaw. Since then, the century-old debate over the location of the teeth of the spiny tooth shark has come to a temporary end. So how do the teeth wrapped in the jaw eat? Further inferences are given in the same article.
CT scan work on the teeth of the spiny shark (Ramsay, 2014)
Restoration diagram based on research
"Ammonite can opener"
The restoration of the muscle characteristics of the spiny tooth shark and the analysis of the mechanical structure of the mouth of the spiny tooth shark have gradually revealed a big secret by paleontologists - the spiny tooth shark loves snail meat!
Ramsay speculated on the feeding patterns of the spiny tooth shark by building a variety of muscle models, and through mechanical structure analysis, it was found that the spiny tooth shark was suitable for feeding on mollusks (especially ammonite) and some small fish. More importantly, this spiral-shaped tooth has its own unique way of eating. When the spiny tooth shark bites the prey, it will bite and loosen, and the spiral teeth will gradually send food into the mouth in the form of a conveyor belt, and in the process the food has been cut into small pieces.
Morphology of oral muscle recovery of spiny shark (Ramsay, 2014)
Simulated feeding of spiny shark (Ramsay, 2014)
Researchers also found that this spiral tooth actually has the function of "shelling"!
When the spiny tooth shark bites the ammonite, it continuously drags the soft part of the ammonite into the mouth through a strong bite force, and the soft part of the ammonite can be easily pulled out of the shell. Eat the whole "field snail" without using any tools. Ammonite, as the overlord who once ruled the entire Ordovician ocean, was ruthlessly ravaged by the spiny shark in the Permian, so the spiny shark gave the nickname "ammonite can opener".
"Persecution of Ammonite"
Model of the mouth of the spiny tooth shark
However, the over-reliance on soft organisms such as ammonites also poses a fatal problem for the spiny tooth shark.
At the turn of the Permian-Triassic period, the largest extinction event in geological history occurred, commonly known as the "P-T mass extinction", and 96% of the species on the earth suddenly disappeared.
This extinction event also caused very serious trauma to mollusks such as ammonites, ammonites are nearly extinct, and although the spiny tooth shark survived this mass extinction event, they quickly fell to the top of the food chain in the early Triassic and gradually went extinct.
At this point, a generation of marine giant spinosaurs has left a legendary story in the geological and historical period, and the world has left mankind with unsolved mysteries for more than a hundred years after 270 million years. Perhaps, the puzzle continues...
The pictures are from the Internet
References
[1] Wikipedia - Genus Spinodont
[2] Wikipedia – Cartilaginous fish
[3] KarpinskyAP. 1899 On the edestid remains and its new genus Helicoprion. Zapiski Imperat. Akad. Nauk 7,1–67.
[4] Tapanila L , Pruitt J , Pradel A , et al. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion[J]. Biology Letters, 2013, 9(2):20130057.
[5] Ramsay J B , Wilga C D , Tapanila L , et al. Eating with a saw for a jaw: Functional morphology of the jaws and tooth-whorl inHelicoprion davisii[J]. Journal of Morphology, 2014.
[6] Zhihu - The Well Frog of Climbing Edge: [Earth Evolution] Yu Teng 4: Wheel
Link: https://zhuanlan.zhihu.com/p/57160311
[7] Zhihu: What strange ancient creatures have existed in the world?
Link: https://www.zhihu.com/question/24176649/answer/27139988
[8] National Geographic: Buzzsaw Jaw Helicoprion Was a Freaky Ratfish
Links: https://www.nationalgeographic.com/science/phenomena/2013/02/26/buzzsaw-jaw-helicoprion-was-a-freaky-ratfish/
Editor: Zhang Yue
Proofreader: Zhang Song