Megalodon

Megalodon Temporal range: Miocene - Pliocene
File:Megalodon tooth.jpg
Megalodon tooth.
Conservation status
Fossil
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Lamniformes
Family:	Lamnidae
Genus:	Carcharodon
Species:	C. megalodon
Binomial name
Carcharodon megalodon Agassiz, 1843

Template:Paleobox Template:Sharksportal The megalodon, Carcharodon megalodon, (from ancient Greek, megas + odon, literally "great tooth") was a giant prehistoric shark that probably lived between about 5 to 1.6 million years ago. As far as we know it was the largest predatory fish to have ever lived.

The megalodon is known principally from fossil teeth and a few fossilized vertebral centra. Like other modern sharks, the skeleton of megalodon was of cartilage and not bone, resulting in the poor skeletal fossil record. However, megalodon's large teeth have survived the ages. The teeth are in many ways similar to great white shark teeth and can measure up to 168 mm (6.61 in) long (maximum slant length).

Recent studies cited by Roesch (see external links below) suggest megalodon was a "close relative" of the great white shark. However, a growing number of researchers dispute this close great white shark–megalodon relationship, instead citing convergent evolution as the reason for the dental similarity. Nevertheless, it is extrapolations from the tooth size of megalodon to modern sharks that provide us with our conceptions about what this ancient superpredator was like.

The best-educated estimates of this creature's maximum size range from 12 to 16 m (40 to 52 ft) (previous much larger reconstructions of the shark's size, up to about 30 m (100 ft), are now generally considered inaccurate).[1] From the size of this shark, its weight is estimated as high as 60 tonnes, though 20 to 30 tonnes was more likely. Assuming similar metabolic-weight ratios as the great white shark, it is estimated that a large megalodon would need to eat about one-fiftieth of its weight of food on average per day. From our knowledge of the food chain during megalodon's existence, it is generally believed that this shark's diet consisted of whale meat.

Taxonomic dispute

There is some disagreement as to how the megalodon should be classified in taxonomy.

• The older view (more favored by marine biologists) is that the megalodon should be classified in the Carcharodon genus with the great white shark, though this has generated debate as to whether megalodon is a direct ancestor of the great white shark or whether the two species share a common ancestor.
• Around 1995, a new genus, Carcharocles, was proposed to classify megalodon. Many paleontologists are now favouring Carcharocles for the shark. Carcharocles proponents give megalodon's likely ancestor as Otodus obliquus from the eocene epoch, and the ancestor of the great white shark not megalodon but Isurus hastalis, the "broad tooth mako". The name Carcharocles is Greek for "Fat beast."

Extinction theories

There is a theory that the adult Carcharodon megalodon fed largely on whales and went extinct as the polar seas became too cold for sharks, allowing whales to swim out of reach of sharks during summer. Other explanations are simpler, suggesting that any prolonged disturbance of the foodchain would wipe out a predator with such massive metabolic requirements. Some cryptozoologists suggest the shark might have died out more recently, or might even still be alive; see "Relict" below. The fossil teeth of the animal are often found in areas that had shallow seas, such as near Bakersfield in California. Megalodon was probably a specialist that fed mostly on baleen whales in shallow waters. A main prey item was Cetotherium. Since the time of its extinction there have been few such shallows supporting constant, large whale populations, and the loss of such habitats caused the animal to gradually go extinct, as the species could no longer find enough food to sustain itself. The process would have been gradual, leading to fewer megalodons, more genetic drift and isolated megalodon populations.

The shark also faced competition from the Killer Whale (or Orca) which evolved less than five million years ago. Populations of "transient" Killer Whales exploit sea mammals, and with pack behavior and high intelligence the Orca would have crowded the shark out of the same declining food source. Once that took place, the shark's huge adult size was of no advantage and in fact meant starvation. The large size of the shark meant it probably hunted alone. It is also likely that Killer Whales preyed on megalodon, at least on younger and smaller ones which shared their range and thus were potential food. As with the relationship between lions and leopards, Killer Whales may have seen the megalodon as potential food, a danger to their young and as a competitor to be killed when possible. Once Megalodon populations went below a certain level, they could no longer find other megalodons of the opposite sex. Thus fewer sharks were born than died, and extinction set in.

Relict

While most mainstream experts contend that available evidence suggests that the megalodon is extinct, the idea of a relict population seems to have seized the public imagination, but evidence supporting such ideas is generally seen as both scanty and ambiguous.

Megalodon teeth have been discovered that some argue date as recently as 10,000 to 15,000 years ago. This claim is based on the discovery of two teeth by the HMS Challenger scientific expedition (these teeth were dated by estimating the amount of time it took for manganese to accumulate on them, although it is quite possible the teeth were fossilized before being encrusted).

Others have countered that these recent estimates for these teeth are inaccurate, and "claims of post-Pliocene C. megalodon ... are erroneous", being based on outdated testing and methodology [2]. Roesch and others also note that megalodons were probably coastal sharks, and that deep-sea survival is extremely unlikely.

Some relatively recent reports of large shark-like creatures have been interpreted as surviving megalodons, but such reports are usually considered misidentification of basking sharks, whale sharks or other large creatures. One well-known example was reported by writer Zane Grey. It is possible, but unlikely, that some of these sightings might be due to abnormally large great white sharks. One famed example was retold by Australian naturalist David Stead. Though widely circulated, this account is generally regarded as of little value, because most of the claimants are anonymous:

In the year 1918 I recorded the sensation that had been caused among the "outside" crayfish men at Port Stephens, when, for several days, they refused to go to sea to their regular fishing grounds in the vicinity of Broughton Island. The men had been at work on the fishing grounds — which lie in deep water — when an immense shark of almost unbelievable proportions put in an appearance, lifting pot after pot containing many crayfishes, and taking, as the men said, "pots, mooring lines and all". These crayfish pots, it should be mentioned, were about 3 feet 6 inches [1.06 m] in diameter and frequently contained from two to three dozen good-sized crayfish each weighing several pounds. The men were all unanimous that this shark was something the like of which they had never dreamed of. In company with the local Fisheries Inspector I questioned many of the men very closely and they all agreed as to the gigantic stature of the beast. But the lengths they gave were, on the whole, absurd. I mention them, however, as an indication of the state of mind which this unusual giant had thrown them into. And bear in mind that these were men who were used to the sea and all sorts of weather, and all sorts of sharks as well. One of the crew said the shark was "three hundred feet [90 m] long at least"! Others said it was as long as the wharf on which we stood – about 115 feet [35 m]! They affirmed that the water "boiled" over a large space when the fish swam past. They were all familiar with whales, which they had often seen passing at sea, but this was a vast shark. They had seen its terrible head which was "at least as long as the roof on the wharf shed at Nelson Bay." Impossible, of course! But these were prosaic and rather stolid men, not given to 'fish stories' nor even to talking about their catches. Further, they knew that the person they were talking to (myself) had heard all the fish stories years before! One of the things that impressed me was that they all agreed as to the ghostly whitish colour of the vast fish. The local Fisheries Inspector of the time, Mr Paton, agreed with me that it must have been something really gigantic to put these experienced men into such a state of fear and panic.

Other references

• A supposed surviving population of megalodon sharks has been the subject of fiction, including several novels by Steve Alten and a feature-length B-movie entitled Shark Attack 3: Megalodon. A big-budget feature film based on Steve Alten's novel Meg is currently in development.
• The videogame Shark! Hunting The Great White features a surviving megalodon in its final stage.
• Megalodon is also a tradename for a make of rebreather for scuba diving.
• Megalodon features in the story Heerser der Diepte (Ruler of the Deep) of the Belgian comic book series De Rode Ridder.
• Heavy metal band Mastodon wrote a song about the megalodon on their 2004 album Leviathan.
• The arcade game Deep Sea Hunters features a megalodon as the leviathan boss

External links

• Megalodon: Shark Glossary
• An impressive photograph of this shark's jaw
• More photos
• A Critical Evaluation of the Supposed Contemporary Existence of Carcharodon megalodon by Ben S. Roesch
• Does Carcharodon Megalodon Still Exist? by Richard J. Ravalli, Jr.
• Reconstructing Megalodon
• Megalodon fact file from BBC, with pictures and video