Sharks are among the most interesting and terrifying creatures on the world, but they are frequently misunderstood and endangered as a result. Thousands of species have swum through the oceans across ages of planetary history, making them some of the oldest still-living fish on the planet.
While there are many sharks still swimming in the water today, there are much more extinct sharks, not to mention some endangered shark species.
1. Megalodon (Otodus megalodon)
Otodus megalodon may have been the most skilled predator ever, capable of hunting the largest turtles, seals, and whales. In fact, Megalodon may be the reason that modern whales, such as humpbacks, migrate into frigid waters on a seasonal basis, as these are the only waters in which Megalodon could not exist.
This adaptation of whales may have been responsible for the extinction of the massive Megalodon, as well as the emergence of a new alpha-predator: orcas. Despite popular perception, today’s great white sharks are not descended from this extinct shark, but rather are connected to Mako sharks.
2. Buzz-saw (Helicoprion)
Helicoprion is another Eugeneodontida member. Because the teeth were uniformly aligned in a helical spiral, the fossils of this shark were initially assumed to be a new type of ammonite. Later research proved that these ‘shells’ were actually shark teeth, but this is where the mystery begins.
These fossils, known as a ‘whorl,’ were always found in the same spiral pattern, and it was discovered that this was how the teeth were organized in the living animal. For a long time, only these tooth whorls were known, but in 2013, the first description of partial skull and jaw cartilage remnants was released.
This was the best recorded clue for Helicoprion’s head form, which put the tooth whorl within a short lower jaw. The fact that fossils of Helicoprion are known from the late Permian and early Triassic periods attests to the genus’s robustness. This demonstrates that Helicoprion survived the Permian extinction, the planet’s biggest extinction event, where about 95% of all animal species were wiped out.
3. Crusher Shark (Ptychodus)
This Ptychodus inhabited the earth between 100 and 85 million years ago, preying on shellfish that it crushed with its powerful jaws. These jaws were armed with approximately 550 gigantic flattening teeth, ideal for devouring the massive amounts of food required by this 11-metre-long behemoth. The gigantic Ptychodus was most certainly the world’s largest shellfish-eating animal.
4. Anvil (Stethacanthus)
Stethacanthus had a more traditional shark shape than Xenacanthus, but it still had two unusual traits that set it apart. Most sharks have triangular dorsal fins, but Stethacanthus‘ dorsal fin was formed like an anvil with a large flattened top.
On top of this dorsal fin was a growth of expanded denticles, larger versions of more normal shark scales that gave the top of the fin a jagged toothed appearance. These larger denticles were likewise localized on the top of the head. Because this “anvil” has only been found on male, experts suspect it was used in their mating ritual.
5. Spiny Shark (Acanthodia)
The Acanthodia was a transitional species between sharks and bony fish (such as tuna) and one of the first creatures to develop a jaw. Its skeleton was comprised of cartilage, like that of current sharks, but its fins were supported by bone spines, like that of ray-finned fish.
The Acanthodia was a filter feeder, possessing cartilage rakes in its gills to catch food particles. It rarely reached larger than 30cm, yet at the time (400 to 360 million years ago), it was the largest filter-feeding animal alive.
6. Scissor Teeth Shark (Edestus)
Edestus, often known as the Scissor Teeth Shark, is another example of the odd shark species that appear to have been most common during the Carboniferous period. However, Edestus is currently classified as a member of the Eugeneodontida, a group of cartilaginous fish that is typically placed within the Holocephalii, closer to chimaeras than real sharks.
Edestus was unique in that as it formed new teeth and gum, the previous tissue was not lost but pushed forward, resulting in teeth that faced forward as they were pushed out of the mouth. To this day, no one knows how Edestus used these fangs to kill and eat prey.
7. Scaleless Shark (Cladoselache)
Cladoselache lived 380 million years ago and retains certain traits of its fishy forefathers. It possessed a fish-like head, seven gills rather than five like most sharks, and a longer and less muscular body than modern sharks. This extinct shark greatest distinguishing trait was that it lacked scales and armor plates, instead opting for thin, brittle scaly skin.
The enormous armored fish Dunkleosteus was the preeminent sea predator during Cladoselache‘s period. Sharks’ only advantage at the time was their speed: being armorless made sharks more sleek and agile.
8. Humped Teeth Shark (Hybodus)
If you ignore the enormous spines that sprang up in front of both dorsal fins, Hybodus looks relatively normal in comparison to some of the other sharks on this list. This extinct shark is one of the rare sharks with recorded body imprints, which has led palaeoichthyologists to believe this shark had two types of teeth.
The front teeth were sharp and pointed, just like most people expect shark teeth to be. The teeth in the back of the mouth were rounded and powerful, and they were effective for crushing the shells of armored animals. Together, these two sets of teeth enabled Hybodus to be an unusually well-balanced generalist predator of a wide range of marine species.
9. Eel Shark (Xenacanthus)
Xenacanthus was a 202 million-year-old freshwater shark that went out. This shark barely developed to a meter in length and resembled eels in appearance significantly more than modern sharks. It featured a long ribbon-like fin extending along its entire back for protection, as well as a sharp spine jutting from the back of its neck.
This spine is thought to have been poisonous, comparable to that of sting. Xenacantus‘s thick V-shaped teeth was probably used to penetrate small prey, like crustaceans and armored fishes.
10. Ginsu Shark (Cretoxyrhina)
Cretoxyrhina had teeth with a thicker layer of enamel than typical, which would have rendered them exceptionally resistant to wear, hence the nickname ‘Ginsu Shark‘ after the knives. Because these teeth were so tough, they are supposed to have been able to cut through bones and shells just as easily as flesh.
Cretoxyrhina lived during the Cretaceous period, when the waters were dominated by giant marine reptiles like mosasaurs. Cretoxyrhina, with a size estimated to have been up to seven meters long (larger even than the largest recorded great white shark), was no pushover, and there are even fossils of mosasaurs found with Cretoxyrhina teeth buried within them.
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