What if a gigantic prehistoric shark — one thought to be extinct for some 2.5 million years — still lurks in the ocean’s depths? That’s the premise of The Meg, a flick which opened August 10. This movie pits massive Carcharocles megalodon against a a handful of resourceful scientists. There’s also a grizzled and fearless deep-sea rescue diver, played by Jason Statham.
The main characters discover the sharks in a deep oceanic trench about 300 kilometers (190 miles) off the coast of China. The film suggests this trench extends more than 11,000 meters (6.8 miles) below the sea surface. That would make it deeper than the Mariana Trench’s Challenger Deep (which is the actual deepest known point in the ocean).
Hydrothermal vents down in the movie’s trench supposedly keep its dark waters warm enough to support an ecosystem teeming with life. And — spoiler alert! — of course, the scientists inadvertently help the giant living fossils escape and head to the surface. There, the megalodons terrorize shark fishermen and beachgoers a la Jaws.
But could a population of these mega-sharks actually have survived down in those mega-depths? Meghan Balk is a paleobiologist who studies the ancient predators. She works at Smithsonian’s National Museum of Natural History in Washington, D.C. And she weighed in for us on what is and is not possible — and what we still don’t know about sharks.
Q: Did megalodons ever actually get as big as they are in the movie? A: Extremely unlikely
Monster-size sharks in The Meg reach lengths of 20 to 25 meters (66 to 82 feet). That’s massive, although a tad smaller than the longest known blue whales. Scientists have made estimates of how big C. megalodon got, based on the size of their fossil teeth. Even the largest reached only 18 meters (about 60 feet). “And that was the absolute largest,” Balk says. On average, C. megalodon tended to be around 10 meters (33 feet) long, she says. That still made them much longer than the length of the average great white shark, which tops out at around 5 to 6 meters (16 to 20 feet). So real megalodons were far smaller than the movie’s versions.
Q: Would a megalodon otherwise look like the film version? A: Yes and no
The movie’s sharks aren’t entirely inaccurate representations, Balk says. Sharks in general have between five and seven gills. The movie’s megalodons correctly have six gills, she notes. And the shape of their dorsal fin is, appropriately, modeled after the great white shark's. The great white is the closest modern relative to the ancient megalodons. Also, a male meg in the film even has “claspers.” These are appendages under the abdomen used to hold a female during mating. “When I looked at it, I was like: ‘Oh, they did a pretty good job,’” Balk says. “They didn’t just create a random shark.”
On the other hand, it’s actually a bit odd that the movie’s megalodons wouldn’t have evolved some significant differences from their prehistoric ancestors, Balk says. “Like the eye getting bigger” to see better, she says. Or maybe they would have become blind after a few million years living in the darkness of the deep sea. You might even expect dwarfism. Populations can shrink in size when they are restricted by geographic isolation — such as potentially being stuck within a trench.
Q: Would such huge sharks have had enough to eat down there? A: Extremely unlikely
In general, Balk notes, “there’s just not enough energy in the deep sea” to sustain giant sharks. Life does bloom at hydrothermal vents. But the deepest known hydrothermal vents are only about 5,000 meters (3.1 miles) deep. And even if there were vents in the deepest trenches, it’s not clear there would be enough big species milling around down there to feed not just one massive shark, but a whole population of them. In the film, the vent field is populated with many smaller species known to cluster around hydrothermal vents. These include shrimps, snails and tube worms. Viewers also see one giant squid. However, there would have had to be a whole lot more food of that size. C. megalodon — like modern great whites — ate many different things, from orcas to squid. And the humongous megalodons in the movie would have needed to eat "a lot of squid,” Balk says, laughing.
Q: Could sharks live at such depths? A: Unlikely
How deep within the ocean sharks can live remains a big unknown. “Quantifying the depth that sharks go to is a big endeavor right now,” Balk says. Few sharks are known to inhabit the abyssal regions — such as sites down to 4,000 meters (2.5 miles) or more. What moves within oceanic trenches more than 6,000 meters (3.7 miles) down is a true mystery. Aside from the scarcity of food, temperatures there could be another limitation to deep-sea living.
There are sharks that inhabit deep parts of the ocean. Among them are goblin sharks and Greenland sharks, which tend to have low metabolic rates. That means they move slowly, Balk says — much more slowly than the energetic predators of the movie. Although C. megalodon cruised seas across the globe, it tended to prefer warm, shallower waters. It even used coastal regions for nursing grounds.
Q: So, could megalodons have survived to modern times without humans knowing about it? A: Extremely unlikely
Sharks shed a lot of teeth throughout their lives. Those teeth are the main fossil evidence of the life and times of prehistoric sharks. Fossilized C. megalodon teeth found in sediments around the world suggest that the creatures lived between about 14 million and 2.6 million years ago. They might not have gone extinct, at the latest, until 1.5 million years ago, Balk says. In fact, it’s not clear why they went extinct. There are, however, a few hypotheses. Perhaps they had to compete for food with too many other creatures, such as orcas. Or they might have been affected by changes in ocean circulation some 3 million years ago, back when the Isthmus of Panama formed. Maybe nearshore nursery sites vanished. Or their prime prey might have disappeared when some marine mammals went extinct about 2.6 million years ago.
Bottom line: The sheer abundance of shed teeth — as many as 20,000 per shark throughout its lifetime — is one of the strongest arguments against megalodon surviving into modern times, Balk says. “That’s one of the reasons why we know megalodon’s definitely extinct. We would have found a tooth.”
abyssal A term that refers to the deepest parts of the ocean.
appendage A finger, leg, ear, antenna or other feature that sticks out from some creature and has some apparent specific function.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
blue whale A species of baleen whale (Balaenoptera musculus) that is the largest animal ever known to have existed. They can grow to lengths of 30 meters (almost 100 feet) and weigh up to 170 metric tons.
dorsal The back of something, usually an animal.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.
extinct An adjective that describes a species for which there are no living members.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
gills The respiratory organ of most aquatic animals that filters oxygen out of water. Fish and other water-dwelling animals use gills to breathe.
hydrothermal vent An opening at the bottom of the ocean or a lake where hot water emerges from deep inside Earth. The water is rich in minerals and chemicals that can nourish ecosystems of worms, clams, microbes and other organisms.
mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
Mariana trench A deep, crescent-shaped canyon running along the Pacific Ocean floor east of the Philippines. It’s massive, some 2,550 kilometers (1,500 miles) long and 70 kilometers (43 miles) wide, on average. The trench marks where two of Earth’s tectonic plates are colliding, forcing one to dive beneath the other.
marine mammal Any of many types of mammals that spend most of its life in the ocean environment. These include whales and dolphins, walruses and sea lions, seals and sea otters, manatees and dugongs — even polar bears.
megalodon An extinct shark species, Carcharocles megalodon, that lived between the early Miocene (an epoch which started some 23 million years ago) and the end of the Pliocene (roughly 2.6 million years ago). Most scientists believe it was the largest fish to ever live. Its name comes from the Greek and means gigantic tooth. The average adult member of this species could have spanned more than 10 meters (33 feet) and weighed 30 metric tons (66,000 pounds) or more.
metabolism (adj. metabolic) The set of life-sustaining chemical reactions that take place inside cells and bigger structures, such as organs. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.
orca The largest species of dolphin. The name of this black-and-white marine mammal, Orcinus orca, means killer whale.
paleobiology The study of organisms that lived in ancient times — especially geologically ancient periods, such as the dinosaur era. Scientists who work in this field are known as paleobiologists.
population (in biology) A group of individuals from the same species that lives in the same area.
predator (adjective: predatory) A creature that preys on other animals for most or all of its food.
prehistoric An adjective for something that happened tens of thousands to millions of years ago, periods before people began deliberately recording events.
prey (n.) Animal species eaten by others. (v.) To attack and eat another species.
random Something that occurs haphazardly or without reason, based on no intention or purpose.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
sediment Material (such as stones and sand) deposited by water, wind or glaciers.
sharks A family of primitive fishes that rely on skeletons formed of cartilage, not bone. Like skates and rays, they belong to a group known as elasmobranchs. Then tend to grow and mature slowly and have few young. Some lay eggs, others give birth to live young.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
squid A member of the cephalopod family (which also contains octopuses and cuttlefish). These predatory animals, which are not fish, contain eight arms, no bones, two tentacles that catch food and a defined head. The animal breathes through gills. It swims by expelling jets of water from beneath its head and then waving finlike tissue that is part of its mantle, a muscular organ. Like an octopus, it may mask its presence by releasing a cloud of “ink.”
vent (n.) An opening through which gases or liquids can escape.
whale A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.