Carcharocles megalodon

The megalodon or megalodon (Carcharocles megalodon; from the gr. μέγας megas 'big', root megal-, and ὀδούς odoús 'tooth', root odont-) is an extinct species of shark that lived between approximately 19.8 and 2.6 million years ago, during the Cenozoic (early Miocene to the end of the Pliocene). It was previously thought to be a member of the Lamnidae family and a close relative of the great white shark (< i>Carcharodon carcharias). However, there is now almost unanimous consensus that it belongs to the extinct family Otodontidae, which diverged from the great white shark ancestry during the Early Cretaceous.

Yeah. C. megalodon is considered as one of the greatest and most powerful predators in the history of vertebrates, scientists differ about whether it would have been more like a more robust version of the great white shark, the pilgrim shark (the pilgrim shark)Cetorhinus maximus) or the shark sand tiger (Carcharias taurus). Most estimates of the size of the megalodonte are extrapolated from the teeth; with estimates of maximum length up to 18 meters and average length estimates of 10.5 meters. Estimates suggest that their large jaws could exercise a bite force of up to 110,000 to 180,000 newtons. Fossil remains indicate that this giant shark had a cosmopolitan distribution, with breeding areas in warm coastal areas. C. megalodon He probably had a very important influence on the structure of the marine communities of his time.

The animal faced competition from whale-eating cetaceans, such as Livyatan and other macroraptorial sperm whales and possibly smaller ancestral killer whales. As the shark preferred warmer waters, it is thought that oceanic cooling associated with the onset of ice ages, along with declining sea levels and the resulting loss of suitable nursery areas, may also have contributed to its decline.. A reduction in the diversity of baleen whales and a shift in their distribution toward the polar regions may have reduced the megalodon's primary food source. A 2019 study reviewed more recent evidence suggesting that competition from the modern great white shark may also have contributed to the extinction of the megalodon, along with range fragmentation resulting in gradual, asynchronous extinction as a result of ocean cooling a few years ago. 3.6-4 million years ago, much earlier than previously assumed. The shark's extinction appears to have affected other animals; For example, the size of baleen whales increased significantly after the shark disappeared.

Discovery

The glossopetræ

According to the ideas of the Renaissance, the gigantic fossil triangular teeth that were frequently found immersed in rock formations were considered petrified tongues (in Latin glossopetræ) of dragons and snakes. This interpretation was corrected in 1667 by a Danish naturalist, Nicholas Steno, who recognized them as belonging to ancient sharks, based on his dissection of a modern shark head. Steno described his findings in a study, Dissection of The head of a shark, which contained an illustration of the head of the current shark along with two glossopetrae, to show and highlight its similarity to the teeth of this animal. According to John Maisey, the Steno plate corresponds to the first known illustration of fossils fromC. megalodon. On the other hand, this study constitutes the first accurate interpretation of the organic origin of the fossils.

Identification

The Swiss naturalist Louis Agassiz gave this shark his scientific name, Carcharodon megalodonin 1835, in his research work Recherches sur les poissons fossiles(research on fossil fish), which completed in 1843. Like teeth C. megalodon are morphologically similar to those of the great white shark, Agassiz assigned the species to the genus Carcharodon. Popularly nicknamed megadity shark, giant white sharkor even shark monster.

There was an apparent description of this shark in 1881, in which it was classified as Selache manzonii.

Fossils

Carcharodon megalodon is represented in the fossil record mainly by teeth and vertebrae centers. Like in the other sharks, the skeleton of Carcharodon. Megalodon. It was formed of cartilage rather than bone; this results in a poor preservation of the found specimens. However, fossil remains of C. megalodon indicate he had densely calcified vertebral centers.

Fossil teeth

The most common fossils of C. megalodonare its teeth. The diagnostic features of the teeth ofC. megalodoninclude: triangular shape, robust structure, large size, a finely serrated edge, and the neck (base of the crown) with a visible letter v shape. The teeth ofC. Megalodonmeasure 18.5 centimeters in perpendicular height and 13.5 centimeters in diagonal length, and are the largest in size of any known species of shark.

Vertebrae

Some fossil vertebrae have been found from C. megalodon. The most notable example is a partially preserved vertebral column from a specimen of C. megalodon, which was unearthed in the Antwerp Basin, Belgium by M. Leriche in 1926. This specimen comprised several vertebral centers, the largest measuring about 155 millimeters in diameter. However, some paleontologists have claimed that they could considerably larger vertebral centers can be expected fromC. megalodon. Bendix-Almgreen (1983) published the discovery of twenty vertebral centers without anatomical connection, but very close to each other, from the clays of the Gram Formation (Denmark). These remains, 100 to 230 millimeters in diameter, showed dense calcification and a concentric structure.

Paleogeographic distribution and age

Fossils of C are known. megalodonfrom different parts of the world, including Europe, North America, South America, Puerto Rico, Cuba, Jamaica, Australia, New Zealand, Japan, Africa, Malta, Grenadines, Canary Islands, and India. Some teeth ofC. megalodonwere discovered in regions far removed from continents (for example, in the Mariana Trench in the Pacific Ocean).

Although the oldest remains from C. megalodonwere reported from late Oligocene strata, about 28 million years ago. A more accepted date for the origin of the species is during the Middle Miocene, about 15.9 million years ago. Despite that the fossil record ofC. megalodon is generally absent in strata later than the upper limit of the Tertiary, there is a more recent record in Pleistocene strata. It is believed that C. megalodon became extinct at the end of the Pliocene, probably about 2.6 million years ago; it is therefore thought that the post-Pliocene teeth reported from C. megalodonare actually reworked fossils.

Anatomy

Among extant species, the great white shark is considered to be the most analogous to C. megalodon. The lack of well-preserved fossil skeletons of C. megalodonhas forced scientists to rely on the morphology of the great white shark to infer its appearance and estimate its size.

Size estimation

Due to the fragmentary nature of the remains found so far, estimate the size of C. megalodonfaces high uncertainty. However, the scientific community recognizes that C. Megalodon was larger than the whale shark (Rhincodon typus). Researchers have directed their studies toward two aspects of size: total length (TL) and body mass (CM).

Total length estimates

The first attempt to reconstruct the jaw of this shark was made by Professor Bashford Dean in 1909. From the dimensions of the reconstructed jaw, it was assumed that C. megalodoncould have approached 30 meters total length (TL) but, in light of new fossil discoveries and scientific advances in the understanding of vertebrates, this reconstruction is now considered to be inaccurate, for two reasons main ones: (1) the relatively poor knowledge of the dentition ofC. megalodonin Dean's time, and (2) inadequate muscular structures. Experts suggest that a rectified version of the jaw model of C. Bashford Dean's megalodon could be about 70% of its original size, a size more consistent with modern finds. To correct the errors, scientists, aided by new fossil finds fromC. megalodonand an improved knowledge of the anatomy of its closest modern analogues, introduced more quantitative methods for estimating size based on statistical relationships between tooth size and body length in the great white shark. Some of the methods are mentioned below.

Method proposed by John E. Randall

In 1973, a Hawaiian ichthyologist, John E. Randall, presented a method for estimating the total length of the great white shark. The proposed method is represented in the form of a plotted graph, which demonstrates the relationship between the height of the crown (the vertical distance of the tooth blade from the base of the enamel part of the tooth to its tip) of the largest of the teeth in the upper jaw of the great white shark and its total length. Randall also extrapolated this method to the total length ofC. megalodon. Randall cited two teeth from C. megalodonin his work: (1) specimen number 10356 from the American Museum of Natural History and (2) specimen number 25730 from the United States National Museum, both of which had a crown height of 115 mm. and 117.5 mm. respectively. These teeth produced a total length of about 13 meters. In 1991, two shark experts, Richard Ellis and John E. McCosker, pointed out a flaw in Randall's method. According to them, the height of the dental crown of sharks does not necessarily increase in proportion to the total length of the animal. This observation led to new proposals to find more accurate methods for determining the size of the great white shark and similar species.

Method proposed by Gottfried et al.

In 1996 three scientists - Michael D. Gottfried, Leonard J. V. Compagno and S. Curtis Bowman - after having carried out a thorough investigation and scrutiny of 73 specimens of the great white shark, proposed a conservative linear relationship between the maximum height of the largest of the upper teeth (DS) and the total length in said shark. The proposed relationship is: the total length (LT) in meters = − (0.22) + (0.096) × [maximum height of DS (millimeters)]. Gottfried and colleagues (1996) also extrapolated this method to estimate the total length ofC. megalodon. The largest tooth ofC. megalodonwithin this team's reach was a maxillary second anterior tooth specimen, the maximum height of which was 168 mm. This tooth had been discovered by Compagno in 1993, and produced a total length estimated at 15.9 meters. However, rumors of teeth larger than C. megalodon persisted at that time. The maximum tooth height for this method is measured as a vertical line from the tip of the dental crown to the bottom of the root lobes, parallel to the long axis of the tooth. In other words, the maximum height of the tooth is the perpendicular height.

Method proposed by Clifford Jeremiah

In 2002, shark researcher Clifford Jeremiah proposed a method to estimate the total length of the great white shark and similar species includingC. megalodon. Researcher David Ward has stated that this method is based on a solid principle that works well with many large sharks. The method itself proposes: "for every centimeter of width of the root of an upper tooth above, there are approximately 4.5 feet (1.3 meters) of shark. Jeremiah noted that the perimeter of a shark's jaw is directly proportional to its total length, with the width of the roots of the largest teeth being an approximation to estimate the perimeter of the jaw. The largest tooth in Jeremiah's possession had one root about 12 cm, which indicates a total length of 15.5 meters.

Method proposed by Kenshu Shimada

In 2002, paleontologist Kenshu Shimada of DePaul University proposed a linear relationship between crown height (CA) and total length (TL) in great white sharks after performing anatomical analyzes of several specimens. In Statistically speaking, this relationship is expressed as: total length (TL) in cm. = a + bx, where a is a constant, b is the slope of the line, and x is the height of the crown (AC) of the tooth in millimeters. This relationship allows the total length to be predicted based on the crown height of any tooth in the great white shark. For this method, the crown height of the tooth is measured as the maximum vertical height of the enamel on the side. labial. Shimada pointed out that the previously proposed methods were based on a weak evaluation of dental homology. Shimada indicated that the growth rate between the crown and the root is not isometric, and this factor must be taken into account in his model.. Furthermore, this proposed relationship can also be used to predict the total length of sharks that are morphologically similar to great white sharks (such as C. megalodon). Using this model, the upper tooth above (with a maximum height of 168 mm.) cited by Gottfried and collaborators (1996) corresponds to a total length of 15.1 meters.

In 2010, several shark researchers, including Catalina Pimiento, Dana J. Ehret, Bruce J. MacFadden, and Gordon Hubbell, estimated the total length ofC. megalodonon the basis of Shimada's method. Among the specimens found in the Gatún formation of Panama, specimen number 237956 produced a total length of 16.8 meters.

Consensus

In the 1990s, marine biologists (such as Patrick J. Schembri and Staphon Papson) felt that C. megalodon could reach a maximum of 24 to 25 meters in total length. The previous estimate of the total length C. megalodon Maybe it's so wild. However, Gottfried and his collaborators (1996) proposed that C. megalodon could measure as much as 20.3 meters in length. Currently the consensus is that this giant shark was more than 16 meters.

Largest known specimens

Gordon Hubbell from Gainesville in the United States, has an upper anterior tooth of C. megalodonwhose maximum height is 184.15 mm. Additionally, a reconstruction of the jaw of C. megalodoncontains a tooth whose maximum reported height is 195.833 mm. This reconstructed jaw was made by the late fossil hunter Vito Bertucci, who was known as the 'Megalodon Man'.

Estimates of body mass

Gottfried and collaborators (1996) also presented a method to determine the body mass of the great white shark after studying the data of the body length-mass ratio of 175 specimens in several stages of growth and extrapolated it to estimate the body mass of the body C. megalodon. The proposed method is: mass in kilograms = 3.29E⁻⁰⁶[LT in (meters)^3.174]. According to this model, C. megalodon 15.9 meters could have had a body mass of about 47 tons, a C. megalodon 17 meters would be about 59 tons, and a C. megalodon 20.3 meters would have a mass of 103 tons. Consequently, C. megalodon is considered as the greatest shark I have ever lived, and is among the greatest known fish that have ever existed.

Dentition and jaw mechanics

A team of Japanese scientists, T. Uyeno, O. Sakamoto and H. Sekine, discovered and excavated partial remains of C. megalodonwith an almost complete collection of teeth found in association, in Saitama, Japan in 1989. Another associated complete teething C. megalodon was excavated in the Yorktown training of Lee Creek, North Carolina in the United States and served as the basis for a reconstruction of the jaw C. megalodon of the American Museum of Natural History in New York. These associated tooth findings solved the uncertainty of how many teeth could be in each row of jaws C. megalodon, allowing more accurate reconstructions of them. More related dentures C. megalodon They have also been found in recent years. Based on these discoveries, two scientists, S. Applegate and L. Espinosa, published a theoretical dental formula (a representation of the teething of an animal regarding the types of teeth and its disposition within the animal's jaw) for C. megalodon in 1996. Modern reconstructions of the jaw C. megalodon are based on this dental formula: ${displaystyle {tfrac {2.1.5.4}{3.0.5.3}}}}}$

As manifested in the dental formula, C. Megalodonhad four kinds of teeth in its jaws.

• Previous - A
• Intermediate - I (In the case of C. megalodon, this tooth seems to be technically an earlier superior and is called "A3" because it is quite symmetrical and does not point medially (the side of the tooth bends towards the middle line of the jaws where the left and right jaws are found), but this tooth is still designed as an intermediate tooth. However, in the case of the big white shark, the intermediate tooth does point on average. This aspect has often been highlighted in the debate Carcharodon versus Carcharocles about megalodon and favors the proponents of its classification Carcharocles.)
• Lateral - L
• Poster - P

C. Megalodonhad very robust dentition, and had a total of about 276 teeth in its jaws, spanning 5 rows. (See "external links" later in the text)

Paleontologists suggest that aC. Very large megalodon would have jaws measuring about 2 meters from one side to the other.

Bite force

In 2008, a team of scientists led by Stephen Wroe conducted an experiment to determine the bite force ofC. megalodon; The results indicate that it had one of the most powerful bite forces in history. AC. The 15.9-meter-long megalodonwas capable of exerting a bite force estimated at 108,514 newtons, and aC. megalodon measuring 20.3 meters long would be capable of exerting a bite estimated at 182,201 newtons.

The bite force of C. megalodon, at its estimated maximum size, is about 28 times larger than the fish Dunkleosteus at 5.3 kilonewtons, about 10 times larger than the great white shark at 18 kilonewton, about 5 times larger than that of Tyrannosaurus rex at 31 kilonewton, and is also larger than that of the pliosaur Pliosaurus funkei at 150 kilonewton.

Additionally, Wroe and colleagues (2008) noted that sharks also shake from side to side when feeding, amplifying the postcranial forces generated. Therefore the total forces experienced by the prey are probably higher than the forces estimated through the experiment. The extraordinary bite force ofC. megalodonmust be considered in the context of the large size of this extinct predator and that paleontological evidence suggests that C. Megalodonwas an active predator of large whales.

Functional parameters of teeth

The exceptionally robust teeth of C. megalodonare serrated, which may have improved their efficiency in cutting the flesh of their prey. Paleontologist Dr. Bretton K. Kent of the University of Maryland suggests that these teeth are very thick for their size, with much lower coefficients of slenderness and flexural strength. They also had substantially larger roots compared to the total height of the tooth, giving them a great mechanical advantage. Teeth with these characteristics not only make good cutting tools, but are also well suited for holding onto powerful prey and would rarely break - even when cutting through bones.

Skeletal anatomy

Apart from estimating the size of C. megalodon, Gottfried and colleagues (1996) also attempted to determine the schematics of the entire skeleton ofC. megalodon.

Mandible structure

To have functional support for its enormous and robust dentition, the jaws of C. megalodonmust have been enormous, thick and more strongly developed than those of the great white shark, which has comparatively more graceful dentition. The strongly developed jaws must have given it a certain appearance of sunken eyes.

Chondrocranium

The chondrocranium of C. Megalodon must have had a more compact and robust appearance than the great white shark, to functionally reflect its more massive jaws and teeth in comparison.

Fins

The fins of C. megalodonmust most likely have been proportionally larger and thicker compared to those of the great white shark because relatively large fins are necessary for propulsion and control of movement in a larger shark.

Axial skeleton

Through scrutiny of the partially preserved vertebrae of the specimen of C. megalodon found in Belgium, it seems that C. megalodonhad a greater number of vertebrae than found in any large specimen of known shark. Only the number of vertebrae of the great white shark comes close in quantity, symbolizing the close anatomical links between the two species.

Complete skeleton reconstruction

On the basis of the characteristics mentioned above, Gottfried and collaborators (1996) reconstructed a complete skeleton of a juvenile individual ofC. megalodon of 11.5 meters in length, which is exhibited at the Calvert Marine Museum on Solomons Island (Maryland, United States). The team emphasized that the different proportions when compared to the skeleton of a great white shark, are based on the same ontogenetic growth patterns of the current great white shark itself.

Paleoecological considerations

Distribution and habitat

Sharks, especially large species, are highly mobile organisms with a complex life cycle and wide geographic distribution. The fossil records of C. megalodonindicate that they were cosmopolitan, and commonly occur in subtropical to temperate latitudes. Before the formation of the Isthmus of Panama, the seas were relatively warm. This made it possible for this species to live in all of the world's oceans..

C. megalodonhad sufficient behavioral flexibility to inhabit a wide range of marine ecosystems (shallow coastal waters, coastal outcrops, swampy coastal lagoons, sandy coastlines, and deep-sea offshore environments), exhibiting a transient way of life. The adults ofC. megalodonwere not abundant in shallow coastal water environments, and mostly lurked offshore. C. megalodonmay have moved between coastal and oceanic waters, particularly at different stages of its life.

Interaction with prey

Sharks are generally opportunistic predators. However, scientists propose thatC. Megalodon was "without a doubt the most formidable carnivore that has ever existed. Its large size, fast swimming ability, and powerful jaws combined into a formidable predatory apparatus, making it a superpredator with the ability to consume a wide spectrum of prey.

Fossil evidence indicates that C. megalodon hunted cetaceans such as dolphins, small whales (including ketotherids such as Piscobalaena, squalodontids, and Odobenocetops), as well as large whales., (including sperm whales, bowhead whales, and fin whales), pinnipeds, porpoises, sirenians, and large sea turtles.

Marine mammals were regular targets ofC. megalodon. Many whale bones have been found with large bite marks (deep cuts) made by teeth matching those ofC. megalodon, and several excavations have revealed that the teeth of C. megalodonlie near chewed remains of whales, and sometimes in direct association with them. There is also fossil evidence of interactions between C. megalodonand pinnipeds. In an interesting observation, a tooth from C. megalodon127mm. It was found very close to a bitten ear bone of a sea lion.

C. megalodon faced a very competitive environment during its existence. However, C. megalodon, being at the top of the food chain, probably had a profound impact on marine communities. The fossil evidence indicates a correlation between the emergence of C. megalodon and the extensive diversification of cetaceans throughout the world. Them C. megalodon Young people preferred regions where small cetaceans were abundant, and adults preferred regions where larger species abound. Such preferences may have developed shortly after their appearance in the Oligocene. Additionally, C. megalodon He was a contemporary of macro-depredator odontocets (especially carnivorous and squalodonated cachalotes), which were probably among the main marine predators of his time, and were a competition. In response to the competition of super-predatory giant sharks, carnivorous odontocetes may have developed some defensive adaptations; some species became hunters in herd, while some species reached gigantic sizes, such as Livyatan melvillei. Still, bite marks on fossil odontocetic remains indicate that they were prey to giant sharks. In addition, fossil evidence indicates that C. megalodon developed the ability to attack large whales. At the end of the Miocene, super-depredatory cachalotes disappeared from the fossil record and left an ecological vacuum.

Like other sharks, C. megalodonmay also have been piscivorous. Fossil evidence indicates that other notable species of apex predator sharks (such as the great white shark) responded to the pressure of competition fromC. megalodonavoiding the areas it inhabited. C. megalodonprobably also had a tendency toward cannibalism. The consumption of prey by C. megalodonseems to have varied by age and location, as with the modern great white shark. It is possible that the adult population ofC. megalodonthat lived along the coast of Peru preferred to frequently hunt cetoterid whales of 2.5 - 7 meters in length and other animals smaller than themselves, instead of whales with the same range of size. size than megalodons. Meanwhile, juveniles would likely have a diet consisting mostly of fish.

Feeding strategies

Sharks often employ complex hunting strategies to target large prey. Some paleontologists suggest that the hunting strategies of the great white shark may offer clues as to how theC. megalodon may have hunted unusually large prey (such as whales). However, fossil evidence suggests that C. Megalodon used more effective hunting strategies against large prey compared to those used by the great white shark.

Paleontologists have conducted a study of fossils to determine the attack patterns ofC. megalodon on its prey. One particular specimen from the Miocene—the remains of a 9-meter-long whale (from an unidentified taxon)—provided the first opportunity to quantitatively analyze the predatory behavior ofC.. megalodon. This hunter focused primarily on attacking the bonier parts (e.g., shoulders, fins, ribs, and spine) of the prey, which great white sharks generally avoid. Bretton Kent indicates thatC. Megalodon tried to shatter the bones and damage the delicate organs (the heart and lungs) housed in the ribcage of the prey. With one attack it could have immobilized the prey, which would quickly die from its wounds. in these vital organs. These findings also make it clear why this prehistoric shark needed more robust teeth than those of great white sharks. Additionally, attack patterns could differ depending on the size of the prey. The fossil remains of Some small cetaceans (such as ketotherids) suggest that they were attacked with great force from below before being killed and devoured.

During the Pliocene, larger and more advanced cetaceans appeared. C. megalodonapparently refined its hunting strategies to deal with these large whales. Numerous fossilized fin bones (pectoral fin segments) and caudal vertebrae of large Pliocene whales have been found with marks that were caused by attacks byC. megalodon. This paleontological evidence suggests that C. Megalodonmight try to immobilize a large whale by destroying its propulsion structures before killing and feeding on it.

Breeding areas

Fossil evidence suggests that the preferred breeding areas of C. megalodonwere warm coastal water environments, where potential dangers were lower and food sources abundant. Some breeding sites have been identified by fossils found in the Gatún Formation of Panama, the Calvert Formation in Maryland, the Banco de Concepción in the Canary Islands and the Bone Valley Formation of Florida. As is the case with many sharks, C. megalodonprobably also gave birth to live young. The size of the teeth ofC. megalodonneonates indicates that the young were between 2 to 3 meters long at birth. Their dietary preferences exhibited an ontogenetic change. The young C. megalodoncommonly hunted fish, sea turtles, dugongs, and small cetaceans; theC. Mature megalodon moved offshore in areas frequented by large cetaceans, which were their main food source. However, there is an exceptional case of a supposedC. young megalodon that tried to attack a large whale, a fin whale. This incident occurred in the Pliocene, 3-4 million years ago, in North Carolina, USA.

Extinction

The cause or causes of the extinction of C. megalodonare still under investigation, however about 3.1 million years ago an important geological event occurred — the closure of the Central American sea passage, which caused significant environmental and faunal changes around the world, probably including the extinction ofC. megalodon.

Ocean cooling and drop in sea levels

The closure of the Isthmus of Panama fundamentally changed global ocean circulation. This event allowed the beginning of a glaciation in the Northern Hemisphere, and later, also facilitated the cooling of the entire planet. Additionally, the expansion of Glaciation during the Pliocene retained large volumes of water in the form of ice sheets, which resulted in a significant drop in sea levels. As a result, during the late Pliocene and Pleistocene there were several ice ages, which cooled the oceans significantly. The main reason cited for the extinction ofC. megalodonis the decline in global-scale ocean temperatures during the Pliocene. This cooling trend adversely impactedC. megalodon, as it preferred warm waters, and as a result became an extremely rare species until its final extinction during the Pleistocene. There is no fossil evidence of C. megalodon in regions around the world where water temperatures had dropped significantly during the Pliocene. Furthermore, these oceanographic changes may have limited many of the warm-water sites that served as breeding grounds for C. megalodon, hindering the maintenance of its population. Breeding areas are essential for the maintenance of a species.

Decline of food sources

Cetaceans reached their greatest diversity during the Miocene, with about 20 recognized genera compared to the six living genera. This diversity represented the ideal framework to maintain a superpredator like C. megalodon. After the closure of the Isthmus of Panama, many species of cetaceans became extinct, and many surviving species disappeared from the tropics. Migration patterns of Pliocene whales have been reconstructed from the record fossil, suggesting that many surviving species showed a tendency to head toward the polar regions. Colder water temperatures during the Pliocene preventedC. megalodon reached the polar regions, and the largest prey were no longer "within range" ofC. megalodonafter these migrations. These events decreased the food sources of C. megalodon in the regions where it lived in the Pliocene, mainly the middle to low latitudes. C. megalodonwas adapted to a specialized lifestyle, which was disrupted as a result of these changes. The extinction of C. megalodoncorrelates with the decline of many small mysticete lineages; It is possible that it was highly dependent on them as a food source. Additionally, the scarcity of prey in the tropics during Plio-Pleistocene times may have fueled cannibalism in theC. megalodon. Young individuals would be at increased risk of attacks by adults during times of famine.

Ecological competition with new species

The appearance and wide distribution of the large predatory dolphinids of the genus Orcinus during the Pliocene probably filled the ecological void left at the end of the Miocene by the disappearance of the super-predatory sperm whales. A minority interpretation indicates that these delphinids may have overcome ecological competition with the latest representatives ofC. megalodonin the top predator niche. However, many experts have inferred that factors such as the cooling trend in the oceans and the decline in prey during the Pliocene may have played a very significant role in the decline and the extinction ofC. megalodon.

The fossil record indicates that these dolphinids commonly appear at high latitudes during the Pliocene, indicating that they were able to cope with the cold water conditions that were becoming predominant, although they have also been found in the tropics (as Orcinus sp. in South Africa). Large bite marks on fossil remains of dolphins indicate that C. megalodon hunted them. However, paleontologist Albert Sanders suggests that C. megalodonhad become too large to sustain itself from the food sources available in the tropics.

Multiple causes

The consensus of experts has indicated that factors such as the cooling of the oceans and the decrease in food sources during the Plio-Pleistocene were a significant factor in the decline of the species.

A study published in 2016 of the distribution and environment of the megalodon over the time of its existence indicated that biotic factors, that is, competition with new predators combined with the reduction in the number of its prey, were the main causes of its extinction. An analysis of the distribution and abundance of this shark throughout the Miocene and Pliocene found no correlation with ocean warming and cooling patterns. Its global decline began at the point where it had reached its maximum geographic range. It was found thatC. megalodoninhabited oceans with a temperature of 12 to 27°C, indicating that the global extent of suitable habitats would not have been greatly affected by the temperature changes that were occurring. This may also reflect thatC. megalodon, like other large sharks, was partially endothermic. Without evidence that temperature restrictions were important, biotic factors involving the decline in cetacean diversity, especially baleen whales, and the increase in Competition with great white sharks, physeteroids and super-predatory dolphins seem to have been mainly responsible for the decline and disappearance of the megalodon.

The body size of baleen whales increased significantly after the extinction of the megalodon (although this could be due to more climate-related causes) Other apex predators appear to have benefited from the disappearance of this formidable species.

Taxonomy

Even after decades of research and scrutiny, the controversy over the phylogeny ofC. megalodonstill persists. Several shark researchers (such as J. E. Randall, A. P. Klimley, D. G. Ainley, M. D. Gottfried, L. J. V. Compagno, S. C. Bowman, and R. W. Purdy) insist that C. Megalodonis a close relative of the great white shark. However, several other experts (such as D. S. Jordan, H. Hannibal, E. Casier, C. DeMuizon, T. J. DeVries, D. Ward and H. Cappetta) reject that proposal and cite convergent evolution as the main reason for the similarity in the teeth of both. The arguments of those who support the genus Carcharocles for C. megalodonseem to have gained notable support. However, the original taxonomic assignment is still widely accepted.

Megalodon within Carcharodon

The traditional view is that C. Megalodon should be classified within the genus Carcharodon along with the great white shark. The main reasons cited for this phylogeny are: (1) an ontogenetic gradation, whereby the teeth of C. carchariasgo from having a coarse serration in the young to a finer serration in the adults, the latter being more similar to those ofC. megalodon; (2) the morphological similarity of the teeth ofC. megalodonyoung to those ofC. carcharias; (3) a symmetrical second anterior tooth; (4) large medial teeth sloping medially; and (5) the upper anterior teeth have the lingual area of the neck of the tooth shaped like a chevron. Supporters of classification within Carcharodon for C. megalodon suggest that C. megalodonand C. carcharias share a common ancestor, Palaeocarcharodon orientalis.

Megalodon inside Carcharocles

Back in 1923, the genus Carcharocles was proposed by two shark researchers, D. S. Jordan and H. Hannibal, to classify the shark C. auriculatus. Later, proponents of Carcharocles assigned C. megalodon to the genus Carcharocles. Proponents of Carcharocles also suggested that the direct ancestor of sharks belonging to the genus Carcharocles, is the ancient giant shark Otodus obliquus, which lived during the Paleocene and Eocene epochs. According to supporters of the classification of C. megalodon in the genus Carcharocles, the phylogenetic line that gives rise to megalodons would be: Otodus obliquus - Otodus aksuaticus - Carcharocles auriculatus - Carcharocles angustidens - Carcharocles chubutensis - C. megalodon. The teeth of Carcharocles chubutensis already show the loss of the small lateral cusps that characterize those of Carcharocles angustidens, definitively absent in C. megalodon. It is even possible that C. megalodon was a species of Otodus. Therefore, some researchers call it Otodus megalodon.

Reconsideration of the megadentate lineage from Carcharocles to Otodus

Shark specialists have been considering returning the entire Carcharocles lineage to the genus Otodus. A 1974 study of Paleogene sharks coined the subgenus Megaselachus, classifying this shark as Otodus (Megaselachus) megalodon, along with O. (M.) chubutensis. A 2006 revision of the Chondrichthyes elevated the name to genus status, reclassifying both species as Megaselachus megalodon and M. chubutensis. The evidence that the megalodon is a member of Otodus was strengthened in 2016 with the publication of a new related genus, Megalolamna. In In their study, Shimada et al. concluded that reclassifying all members of Carcharocles into Otodus is necessary to make Otodus i> monophyletic, and that Otodus is the sister clade of Megalolamna within the family Otodontidae. In turn, within the genus Otodus, it is considered that O. obliquusis the sister taxon to the megadentate shark lineage.

Megalodon as a chronospecies?

Researcher David Ward has further elaborated the evolutionary process of Carcharocles by implying that this lineage, which extends from the Paleocene to the Pliocene, is from a single giant shark which changes gradually over time, suggesting a case of chronospecies.

A new evolutionary position for the great white shark

Proponents of Carcharocles noted that the great white shark is most closely related to the ancient shark Isurus hastalis, known as the "broad-toothed mako", that aC. megalodon. One reason cited by paleontologist Chuck Ciampaglio is that the dental morphometry (intraspecific variations in measurements and changes in the physical shape of teeth) of I. hastalisand C. carchariasare remarkably similar. Another reason cited is that the teeth of C. megalodonhave much finer serrations than those of C. carcharias. Additional evidence, linking the great white shark more closely to ancient mako sharks than to C. megalodon, was published in 2009: fossils of an ancient form of the great white shark, dated to about 4 million years ago, and which had been found in southwestern Peru in 1988. These remains show a probable ancestor shared by modern makos and modern great white sharks.

Controversies

Wright State University paleontologist Chuck Ciampaglio says the similarities between the teeth ofC. megalodonand those of the great white shark are superficial and have notable morphometric differences between them, and these findings are sufficient to justify a separate genus for C. megalodon. However, some supporters of the genus Carcharodon for C. megalodons (like M. D. Gottfried and R. E. Fordyce) have provided further arguments for a close relationship between extinct megadentate sharks and the great white shark. With respect to the recent controversy concerning the relationships between lamnid sharks, the morphology completeness—particularly the internal calcification patterns of the vertebral centers of the great white shark—has been compared to that of the well-preserved vertebral centers of megadentate sharks, includingC. megalodonand C. angustidens. The apparent morphological similarity supports a close relationship of the fossil megadentate species with extant great white sharks.

With respect to the origins of the great white shark, Gottfried and Fordyce have pointed out that some fossils of great white sharks are about 16 million years old and predate fossils from the Pliocene transition (5.3 million years ago). Additionally, the Oligocene records ofC. megalodon, contradict the suggestion that Carcharocles chubutensis is the immediate ancestor of C. megalodon. These records also indicate thatC. megalodon actually coexisted with Carcharocles angustidens. Therefore, supporters of the genus Carcharodon for C. megalodon argue that extinct megatooth sharks should be included in the genus Carcharodon.

Some paleontologists argue that the genus Otodus should be used for sharks included in the lineage Carcharocles and that this genus should be discarded.

At present, several of the supporters of the genus Carcharocles for C. megalodon (like Catalina Pimiento, Dana J. Ehret, Bruce J. MacFadden and Gordon Hubbell) accept that both species belong to the order Lamniformes, and that in the absence of living members of the family i>Otodontidae, the great white shark is the best ecological analogy for C. megalodon.

Current survival

Although experts believe that there is no evidence available to indicate that the megalodon is not extinct, the idea that a surviving population could continue to exist today seems to have settled into the public imagination.

The idea of its recent survival is usually inspired by the discovery of a tooth ofC. megalodonby members of the ship HMS Challenger in 1872, which some believed was only 10,000 years old. However, this tooth has been reexamined, and findings indicate that its age is imprecise. Analyzes of two Megalodon teeth found by the HMS Challenger give a date of between 10,000 and 15,000 years old, an estimated time for the deposition of the amount of manganese accumulated on them. However, it is quite likely that the teeth were already fossilized before the manganese crust developed on them, so their origin would be much older and would not have anything extraordinary. Several authors believe that recent estimates for these teeth are imprecise and that any assertion of the existence of Carcharodon megalodon in post-Pliocene times is simply erroneous, based on outdated methodology and experiments. Roesch and others emphasize the fact that megalodons were probably coastal animals (like white sharks), so survival at the bottom of the oceans would be extremely unlikely.

The megalodon in fiction

Since the remains of C. megalodonwere discovered, they have been an object of fascination. It has been portrayed in various works of fiction, including films and novels, and continues to maintain its place among the most popular subjects of fiction involving sea monsters. Many of these fictional accounts posit that at least one relict population ofC. megalodonsurvived extinction and lurks in the vast depths of the ocean, and some individuals managed to reach the surface from deep, either by human intervention or by natural means. The story of Jim Shepard "Tedford and the Megalodon" is a good example of this.

Some works of fiction (such as Shark Attack 3: Megalodon, and Steve Alten's "Meg" series, and even Megalodon) represent incorrectly toC. megalodonas a species more than 70 million years old, being alive at the time of the dinosaurs. The writers of the movie Shark Attack 3: Megalodon represented this idea by including an altered copy of a book by shark researcher Richard Ellis, called 'Great White Shark'. The copy shown in the film had several pages that do not exist in the real book. The author sued the film's distributor, Lions Gate Entertainment, seeking an end to distribution of the film, along with $150,000 in damages. Steve Alten's novel Meg: A Novel of Deep Terroris known for portraying this error with its prologue illustrations and cover featuring C. megalodonkilling a tyrannosaurus in the sea. And finally, the 2004 film, Megalodon, shows the error in a scene of the film, one of the protagonists saying that the Megalodon became extinct 65 million years ago.

The films Mega Shark Versus Giant Octopus (2009) and its sequel Mega Shark Versus Crocosaurus (2010) are parodies of disaster films featuring a giant megalodon-like shark. in the lead role.

In August 2013, the Discovery Channel began its annual Shark Week event with Megalodon: The Monster Shark Lives monster lives"), a controversial mockumentary about the supposed existence of this creature. This program has been criticized because it is completely fictional; For example, all the supposed scientists represented were actually actors. The supposed photograph shown in the program, taken in December 1942, where a Megalodon could be seen swimming next to a submarine, quickly went viral on the Internet, but was demonstrated that it is manipulated based on archival footage of submarines in the Atlantic during World War II. In 2014, Discovery re-aired "The Monster Shark Lives," along with a new hour-long show, "Megalodon: The New Evidence" (Megalodon: The New Evidence), and an additional dramatized program titled Shark of Darkness: Wrath of Submarine, which ended in a greater rejection from the media and the scientific community.

The movie Megalodon (2018) has been the latest fictional medium where the prehistoric shark is shown, with the hypothesis that the megalodon was hiding in the depths of the Pacific Ocean and that it would come to light. surface after being disturbed by humanity, and with the aim of devouring Jonas Taylor (Jason Statham) and his crew.