The megalodon (or MEG-a-la-don; meaning "big tooth" or in Greek as μέγας 'οδόντος) was a giant shark that lived in prehistoric times, between about 18 million to 1.5 million years ago and was the apex predator of its time. The oldest C. megalodon teeth found are about 18 million years old. C. megalodon became extinct in the Pleistocene epoch probably about 1.5 million years ago. It is the largest carnivorous fish known to have existed, and quite possibly the largest shark ever to have lived.
Scientists suggest that C. megalodon could grow to more than long. This species is a member of the Lamnidae family but its classification is in dispute and a new genus has been proposed. Fossil evidence has revealed that megalodon fed upon large animals, including the early whales.
|2=C. megalodon}} }} }} *Note: The hastalis hypothesis shows that C. carcharias is more closely related to I. hastalis than C. megalodon. There is a major disagreement among scientists as to how C. megalodon should be classified. The controversy is that whether C. megalodon is a close relative of the extant great white shark or whether the two species are distant relatives. The trend among shark researchers is to dismiss the statement that C. megalodon is a close relative of the great white shark, in favor of citing convergent evolution as the reason for the dental similarity.
Carcharocles proponents also point out that the great white shark is more closely related to an ancient shark Isurus hastalis, the \"broad tooth mako,\" than C. megalodon. This suggestion is given credence by many scientists due to some convincing evidence. One reason is that the teeth of I. hastalis and C. carcharias are remarkably similar in shape, differing only in that the former lack the characteristic serrations of the latter.
C. megalodon is known primarily from fossil teeth and a few fossilized vertebral centra. As with all other sharks, the megalodon skeleton was formed of cartilage and not bone, resulting in a poor skeletal fossil record. The teeth are in many ways similar to great white shark teeth but are much larger and can measure up to more than 18 cm in slant.
Nevertheless, it is extrapolations from the shape and size of the teeth of C. megalodon when compared with related modern sharks and studies of their physical characteristics, that provide us with our conceptions about what this ancient superpredator might have looked like in life. Thus far, the great white shark has been considered the favored model for the basis for the reconstruction of C. megalodon.
Estimating the maximum size of C. megalodon is a highly controversial subject. An early jaw reconstruction of this shark, developed by Professor Bashford Dean in 1909, indicates a length of more than , but that jaw reconstruction is now considered to be inaccurate. One reason is that the teeth used as posteriors in this jaw reconstruction were not true posterior teeth. However, several scientists have tried to solve this issue in later years.
In 1973, the ichthyiologist John E. Randall suggested a method to measure the size of the large sharks. According to Randall, the enamel height of the largest tooth in the upper jaw of the shark can be used to determine its total length. He concluded that C. megalodon could grow to .
However, in 1996, three shark experts, Michael D. Gottfried, Leonard J. V. Compagno and S. Curtis Bowman, questioned the reliability of Randall's method. According to them, shark's tooth enamel height does not necessarily increase in proportion with the animal's total length. Gottfried and his co-workers tried to solve this issue by means of conducting new research and analysis to create a method for measuring the size of large sharks (including C. megalodon) with much greater accuracy, which was published in 1996. The proposed method is: "Megatooth's" Total Length in meters = [− (0.22) + (0.096) × (Slant height of tooth in [mm])]. This method has often been interpreted as: "Megatooth's" Total Length in meters = [(0.96) × (Slant height of tooth in [cm] − (0.22))], because it yields same results. Using this new method, the maximum size of megalodon was calculated to be with a body mass of more than . But this calculation was based on a 168 mm (6⅝ inch) long upper anterior tooth, which was the biggest tooth in the possession of this team at the time. Since then, even larger C. megalodon teeth have been excavated which indicate that the shark could grow to more than .
Shark researcher Cliff Jeremiah also has suggested a method to determine the size of the large sharks, including C. megalodon, and his method is considered to be among the most reliable. He suggested that the jaw perimeter of a shark is directly proportional to its total length, with the width of the roots of the largest teeth being a proxy for estimating jaw perimeter. For every centimeter of root width of the largest tooth, he asserts, there was approximately 4.5 feet of the shark. He concluded that C. megalodon could grow up to . Many scientists acknowledge this conclusion.
Hence, from the research of several scientists, it is clear that C. megalodon is the largest macropredatory shark that has ever lived and is among the largest fishes known to have existed.
A team of Japanese scientists, T. Uyeno, O. Sakamoto, and H. Sekine, discovered and excavated the partial remains of a C. megalodon, with nearly complete associated set of its teeth, from Saitama, Japan in 1989. Based upon this discovery, two scientists, S. Applegate and L. Espinosa, published an artificial dental formula for C. megalodon in 1996. Several modern C. megalodon jaw reconstructions are based on this dental formula.
The dental formula of C. megalodon is:
As evident from the dental formula, C. megalodon contained four different kinds of teeth in its jaws.
Paleontologists suggest that C. megalodon had a very robust dentition, and it had a total of about 250 teeth in its jaws.
Gottfried and his colleagues eventually developed a model of the entire skeleton of C. megalodon with the above mentioned characteristics, which has been put on display in Calvert Marine Museum at Solomons island, Maryland in USA.
C. megalodon most likely inhabited warm water regions around the world. Its range would not have been constricted by its reliance on warm waters as the oceans were noticeably warmer during the Miocene and early Pliocene. This would have made it possible for this species to flourish around the world, as evident from the fossil records.
However, remains of a large prehistoric baleen whale have been excavated from Chesapeake Bay, which provided the first opportunity to quantitatively analyse the feeding behavior of C. megalodon, and this specimen revealed that the attacking behavior of C. megalodon may have been more aggressive than that of the great white shark. One reason is that the shark apparently focused its attack on the bony portions of the prey, which great white sharks generally avoid.
From fossil evidence, juvenile C. megalodon individuals would mostly prefer to attack small-to-medium sized prey, such as porpoises, other sharks, pinnipeds and juvenile whales. Hence, through ontogeny C. megalodon proceeded to hunt larger animals. In addition, fossil evidence suggests that the preferred breeding grounds of C. megalodon were mostly warm coastal regions.
There are several hypotheses as to how an apex predator like C. megalodon suddenly became extinct after millions of years of existence. However, the extinction of large-bodied marine predators, such as pliosaurs, mosasaurs, ichthyosaurs and Basilosaurus, are instructive as to the possible mechanism involved.
Scientists believe that C. megalodon disappeared due to a variety of reasons. The geological and climatic conditions of the world when C. megalodon existed, were considerably different from those now. It is possible that these major climatic changes may have been unfavorable for C. megalodon. Some notable climatic shifts are:
Consequently, a hypothesis can be constructed, that at the end of the Pliocene, the polar seas became too cold for C. megalodon to survive. Several species of whales, including cetotheriids, became extinct during the late Pliocene, while some whale species showed a trend towards the cooler polar regions. Many of the shallow warm water regions dried out at that time, that may have been breeding grounds for C. megalodon. As such, these significant disturbances in the ecosystem would have caused major problems for C. megalodon. Being unable to follow the surviving whale species into the polar seas the food supply of C. megalodon lessened, which over time lead to the extinction of the species.