Nothing evokes primal terror in humans more than the sight of a single, curved fin cruising through a shallow sea. A shark has been sighted! But these ancient fish don’t exist simply to terrify humans. Sharks and rays are a diverse group that come in many shapes and sizes and exist in a wide variety of ocean environments. After millions of years as lords of the ocean, sharks have become threatened in modern times, as overfishing endangers their populations across the world. Only in modern times have people begun to learn extensively about the life cycles and habits of many shark species in hopes of preserving them. You can learn about them, too, from many books on sharks in CRRL’s collection! Join us as we explore fascinating facts about sharks and rays.
Before the Human Age: Sharks in the Fossil Record
Sharks are one of the oldest groups of fish still in existence, with a history in the fossil record dating back over 400 million years. Despite this, high-quality shark fossils are quite rare because their skeletons are made of cartilage rather than bone. The only parts of shark bodies made of harder material are their teeth (which are bone) and some of the scales on their bodies. Early sharks from the Devonian period (about 419-359 million years ago) looked quite different from today’s sharks and filled many of the roles that bony fishes have in today’s ecosystem. Some of these were even freshwater sharks, a trait that is rare today.
Sharks survived a great extinction at the end of the Devonian and became quite diverse in the next age, the Carboniferous. One of the most bizarre of Carboniferous sharks was Helicoprion, the “buzzsaw shark.” This creature’s lower jaw was a circular whorl of teeth, and it could roll them back and forth to cut through soft-bodied prey, such as squid. Another strange shark of the Carboniferous was Stethacanthus, a shark with a dorsal fin that resembled a giant brush covered in toothlike scales. Falcatus, a 10-12-inch-long shark with a strange sickle-shaped dorsal fin on male individuals, also stands out as representative of the many strange forms now-extinct sharks could take.
At about 252 million years ago, the Permian period ended, and many of these distinct groups of ancient sharks vanished from the seas forever in the Great Dying. Only a few groups would survive this extinction event, which killed off 81% of all marine species. In the early Jurassic, the first group of modern sharks, the Hexanchiformes (six-gill sharks) arose and were followed by the other groups of modern sharks and rays. Many species of modern sharks have gone extinct over the years, among them the mighty Megalodon. This powerful carnivore was over 50 feet long and roamed the oceans around the world in search of whales to devour. Megalodon is often depicted in various media as looking like an enormous great white shark and is sometimes given the inaccurate name “Jurassic Shark.” In reality, Megalodon lived from about 23 to 3.5 million years ago, long after the Dinosaur Age, and little is known about its actual appearance because the only fossils we have are their teeth. You can search for Megalodon teeth on any of Virginia’s beaches and coastal areas, including Westmoreland County!
Ocean Overlords: The Sharks and Rays of Our Age
Many different types of sharks remain in our oceans today. Most of them are no threat to humans, preferring different types of food. The largest shark species alive today, the whale shark, is a filter feeder that eats only tiny krill, fish eggs, and plankton. It is a slow swimmer that can be found in tropical to subtropical waters around the world. Its appearance is noteworthy for its distinctive spotted patterns and the massive gape of its mouth. Whale sharks are placid and nonthreatening to humans, and divers have often been filmed swimming with them. Only two other sharks are filter feeders: the basking shark, which can swim in colder water than the whale shark, and the megamouth shark, a deep sea swimmer rarely seen by humans and only discovered in 1976.
Closely related to true sharks are the bottom-feeding rays and sawfish, which have downward facing mouths and teeth specially adapted for crushing hard crabs and oysters. Rays typically live on the ocean floor and swim across it with their broad, flat pectoral fins. Many rays rely on camouflage to protect themselves, although the stingrays also have a venomous spine on their tail that can be extremely dangerous. Sawfish are a particularly large type of ray that have a large rostrum or “saw” with teeth on its sides attached to their head. The sawfish thrashes the rostrum from side to side while swimming to stun schools of small fish so it can feed, and it can also use it as a weapon to fight off predators. The largest of all rays are the manta rays, which live quite differently from other kinds of rays. Manta rays swim through the open ocean rather than living on the sea bottom, are filter feeders similar to whale sharks, and are harmless to humans, lacking a tail stinger.
Most shark species are not dangerous to humans. Humans have existed in the open ocean for only a brief period of time, and sharks aren’t adapted to eating humans as a natural prey. The vast majority of shark species can’t eat humans, because of differences in size and their tooth structure. However, a select few species are quite dangerous to humans and should be avoided whenever possible. The oceanic whitetip typically doesn’t come close to shore but is a danger to shipwreck survivors and is remembered for its attacks on sailors after the sinking of the USS Indianapolis in 1945. Noted for the striped pattern on its back, the tiger shark is a generalist feeder that is attracted to seashores where large numbers of animals gather, which can include nesting turtles, birds, and humans on vacation. Great whites are the largest predatory shark and get the most media attention as “man-eaters.” However, their preferred prey is seals, and they often attack humans because they mistake a person on a surfboard for a seal. Perhaps the most dangerous sharks of all to humans are the bull sharks, which tend to live in shallow water and are so tolerant of freshwater that they can swim up rivers. Their habitat is quite close to humans, and they are quite aggressive, often head-butting their target before biting.
A Dangerous Age: The Threats to Sharks
Images of sharks have been overwhelmingly negative in Western media for centuries. One of the earliest works depicting a shark attack was Watson and the Shark, an oil painting of a young boy being attacked by a great white off the coast of Havana. The picture is a romanticized depiction of an actual shark attack from 1749, in which Brook Watson was attacked at the age of 14 by a shark while swimming alone. Little research would be done on sharks in the centuries following Watson and the Shark, and sharks would remain objects of menace and mystery that would only be discussed after the occasional shark attack. The negative associations would be further cemented by the 1916 shark attacks, in which a large shark swam up the coastlines and creeks of Matawan, New Jersey, and killed four people in separate attacks. The attacks stopped after a 350-pound great white was killed in the open ocean. It was believed at the time that this shark was responsible for the attacks, but some of the attacks occurred in creeks far inland from the sea, in places only a bull shark could go. The concept of a great white attacking multiple people would remain in people’s minds for decades, though, and would live forever through the popular novel and film Jaws.
Over the 20th and 21st centuries, populations of some species of sharks and rays have become endangered all over the world. Large, slow-growing species are particularly threatened. Whale sharks have been classified as endangered since 2016, with fishing for the Asian shark-fin soup market posing a particular threat to their long-term survival. The giant manta ray has also been listed as endangered since 2020, as a market for their gill plates (which they use to feed off plankton) has developed in some Asian countries. Sharks that are dangerous to humans have suffered population declines as well. The great white shark has had its population decline to the point it is considered vulnerable, due to sport fishing from its ferocious reputation, as well as accidental deaths in commercial fishing nets. The list of threatened shark species is quite extensive, and 36 percent of all shark and ray species are threatened.
In this time of danger, humans still have much to learn about sharks. Keeping sharks in captivity has proven quite difficult and requires an enormous tank and financial resources. The Georgia Aquarium is one of the few places you can see a captive whale shark. Manta rays are almost as uncommon in captivity, restricted to single aquariums in the United States, France, and a few more worldwide. And the great white has never been kept successfully in captivity for long. The longest a great white lasted in captivity was 200 days, and a great white has never bred under human care. Shark research relies on observations of wild individuals, and makes use of acoustic transmitters to track and observe their motions. Tagging sharks allows researchers to observe shark populations and determine how they interact with each other. Through recent research, we have learned that “solitary” sharks may have social relationships, and that manta rays are intelligent enough to pass the mirror test for self-awareness. Who knows what else we’ll learn in the next decades?
You can learn more about sharks and rays from CRRL’s collection. We have many books about the different species of sharks, their habitats, and their hunting methods. Unravel the mysteries of these great predators of the ocean during Shark Week—or any week—at your local CRRL branch. If you want to venture even further into the world of sharks, two aquariums in our area feature them. The National Aquarium in Baltimore features Shark Alley, where you can see sawfish, nurse sharks, and stingrays in a 225,000-gallon tank. Virginia Aquarium in Virginia Beach has sandbar sharks, nurse sharks and sand tiger sharks. Consider a visit to CRRL and a field trip to an aquarium. You’ll be surprised with all that you learn!
Good educational books on sharks and rays for various ages. Includes a streaming video for children.