By Spielberg's famous work "The Great White Jaw", when we mention sharks, we often think of a nimble figure that is shuttled through the water, plus a terrifying bloody mouth. But there is actually a certain stereotype , because most species of sharks have a mild temperament and will not hurt people. You should know that there are more than 530 species of sharks in the world, and there are only a dozen of them that have had records of injury. The whale shark, which is the largest in the current fish, can be more than 10 meters long. Although it is very large, they filter foods such as algae , krill, and small fish, which has nothing to do with the fierce and mighty image of the shark in our impression. However, as the saying goes, "Good things don't go out, bad things go thousands of miles away." Because these few terrifying sharks represented by great white sharks leave us with an impression that they are too impactful, we often ignore the gentle images of most other sharks.
Great White Shark. Image from British photographer Euan Rannachan
The famous novelist Hemingway once described the cruelty of sharks in his novel "The Old Man and the Sea": "It is these sharks, with only thick and sharp blue heads, huge eyes, and aggressive mouths that make a crack and swallow everything. When they are hungry, they will not even let go of the oars or rudders on the boat. They will bite off their feet and fin-like limbs while turtle is asleep on the water. ;If they are really hungry, they will even attack people in the water, even though there is no fish's smell or fish's mucus on them. They are killers who do evil."The huge and ferocious Megold shark in " Megold shark " released in recent years has raised our horror impression of sharks to a new level. Such a prehistoric hamlet that has been considered to be a long-lost prehistoric giant shark suddenly appeared in front of the world like a nightmare, and started killing, and the impact it brought can be imagined. However, the giant shark in "Megalodon" is not completely fictional. Such sharks do exist before history. Its mere tooth is 15-16 cm in size.
Movie "Megalodon" poster
Researcher Gai Zhikun from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences shows the fossils of the tooth of the Megalodon shark (photo provided by Gai Zhikun)
In fact, what we currently call sharks generally refer to most members of the , but in a narrow sense, they only refer to the new sharks in the phalanx subclass of cartilage fish. The sharks are located in the Cartilage Class has a very long evolutionary history. They were born from ancient shield-skinned fish more than 400 million years ago and had parted ways with our ancestors more than 400 million years ago. In the early Shiliu world more than 400 million years ago, the earliest cartilage fishes - the Fanjing Mountain and the double-row Guizhou-toothed fish of the cartilage fish apricot and the double-row Guizhou-toothed fish appeared in the Devonian . However, the cartilage fishes were not big in size during this period and basically lived under the shadow of sea scorpions or terrors. This can be reflected in their fossil size, distribution and number.
One of the earliest cartilage fish --Xinsu Fanjing Mountain Fish. The picture comes from Plamen et al. 2022
Silurian late ecological restoration map. The blue fish near the middle of the water surface is an early cartilage fish - Spinelid . Image source: M. Hattri
290 million years ago, a group of ferocious "sea monsters" appeared on the earth in the vast oceans around the world. The most representative of them are the calves and spiral sharks. By the time of Triassic to the Jurassic period, the real sharks in the Plate Gills actually rose.
The pioneer of real sharks - sausage shows off her skills in the Triassic ocean. They are very wide-ranging. In addition to saltwater oceans, they even spread their footprints to inland freshwater lakes to prey on smaller animals in the waters.
By the Cretaceous period, we could see tiger sharks, whiskers , flat sharks , cat sharks and these real sharks that we still have in the ocean.At this time, there are two outstanding representatives of sharks, namely the chalk pointed shark and the horn scale shark. The former may be similar to our great white shark today, and the latter is similar to today's Gu's weasel shark . We can see tooth fossils embedded by horn scale sharks in many scattered animal bone fossils in the Cretaceous strata.
Two hungry horn scale sharks are attacking a dead duck-billed dragon . Image source: Wikipedia
When we arrived at the new era, the megalodon sharks that we are familiar with appeared in movies emerged and became the well-deserved overlord of the Third Age ocean. This prehistoric giant shark with an average length of 14 meters (sung as high as 4-5 floors!) and a maximum bite force of 20 tons may be one of the strongest bite creatures found in the history of the earth. In front of it, whales, king squid , etc., which are already heavyweight enough, all appear vulnerable. People have been studying this shark for nearly 400 years, and some new technologies and methods used by paleontologists in recent years have further confirmed the dominance of megalodons. In this year's article published in Science Advanceds, Cenozoic megatooth sharks occupied extremely high trophic positions In the cover article, paleontologist Kast used the correspondence between the content of nitrogen-15 isotopes in the enamel and dentin of modern marine animals, , and its position in the food chain (i.e., the higher the ratio of nitrogen-15 in the teeth, the more nutrients the organism consumes, and the higher the level of the food chain). He found that the ratio of nitrogen-15 in the enamel of megalodon was much higher than that of modern great white sharks, polar bears , and orcas, which showed that the nutrition level of megalodon was very high and indeed stood at the top of the entire food chain at that time.
The relationship table of the body size and influence level of megalodon and the nitrogen isotopes on its enamel surface (Picture from Emmaet, al. 2022)
is also another journal published in Science Advances this year. Paleontologist Jack Cooper calculated a complete megalodon model based on three-dimensional data of the spine and teeth of the ear-shaped megalodon combined with the soft skull reconstruction of the living great white shark. The calculated results show that the ear-shaped megalodon shark is more than 15 meters long, weighs 6156 kilograms, and swims faster, with the ability to cross the ocean and actively prey on large prey.
JackCooper uses the teeth of the megalodon and the skull of the present great white shark to reconstruct the 3D model of the megalodon shark (Picture from JackCooperet, al. 2022)
Comparison of the size of all sharks since the Mesozoic Era, among which the gray genus group (Picture source Kenshu Shimada, DePaul University)
However, the fate of cartilage fish is very unfortunate. It took them a full 400 million years before the megalodon has settled as the dominant position of the ocean, but this prosperity has not lasted for much success. The megalodon has lived on Earth for 20 million years, but suddenly became extinct in the Pleistocene 2 million years ago, which is likely to have a lot to do with the sudden cold climate. Although this is a shark's misfortune, it is also a blessing for us humans to a certain extent. Imagine that if there are such monsters in the sea, then the horror plot of the movie "The Megdolite" may have really come true.
References:
[1]Andreev, P.S., Sansom, I.J., Li, Q.et al.Spiny chondrichthyan from the lower Silurian of South China.Nature609, 969–974 (2022). http://doi.org/10.1038/s41586-022-05233-8
[2]Nicholas D. Pyenson, Paul L. Koch, Oh, the shark has such teenth: Did megatooth sharks play a larger role in prehistoric food webs?, Science Advances, 8, 25, (2022).
[3]Cooper JA, Hutchinson JR, Bernvi DC, Cliff G, Wilson RP, Dicken ML, Menzel J, Wroe S, Pirlo J, Pimiento C. The extinct shark Otodus megalodon was a transsoceanic superpredator: Inferences from 3D modeling. Sci Adv. 2022
[4]Kenshu Shimada, Martin A. Becker Michael L. Griffiths (2021) Body, jaw, and dentition lengths of macrophagous lamniform sharks, and body size evolution in Lamniformes with special reference to ‘off-the-scale’ gigantism of the megatooth shark, Otodus megalodon, Historical Biology, 33:11, 2543-2559, DOI: 10.1080/08912963.2020.1812598
Produced by | Popular Science China - Creation and Cultivation Plan
Author | Lin Xianghong
Review | Gai Zhikun Researcher at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PhD supervisor
