Sharks are 450 million years old and have been on this planet longer than almost any other animal. They have lived through every major mass extinction event and have survived long past many of their competitors. With over 3,000 species spanning nearly half a billion years, sharks are one of the most evolutionarily successful species to ever live. Tracking their evolutionary history, we can learn about these amazing species and how they came to their modern forms.
The Silurian Era: The First Sharks
450 million years ago, during the Silurian period, sharks first began developing as a unique species. During that time, the ocean was filled with a variety of bony fish. One of these fish, the Acanthodian, was the very first ancestor of the modern shark. Acanthodians, also called “spiny sharks,” were the first fish to not only take on the physical characteristics of a shark, but to develop the cartilaginous skeletal structures that define sharks. All sharks living today have evolved from this early fish.
Early Devonian Era: Shark Evolution Begins
About 50 millions years of after the SIlurian Era, the Devonian Era began. This is when the very first, fully developed shark, the Leonodus Shark, evolved. Very little is known about the leonodus shark. However, the fossil remains of its two-pronged teeth lead scientists to believe that it was about 16 inches long, with an eel-like body and lived in freshwater. Another freshwater shark discovered from this period was the Antarctilamna. The Antarctilamna was also eel-like but had a small fin behind it’s head. Both of these species are considered to be in the now extinct early shark genus Xenacanthus.
Late Devonian Era: The First Modern Shark
During the late Devonian Era, the first shark in its modern incarnation appeared, the Cladoselache. The Cladoselache differed from its eel-like ancestors, because it’s body looked more like what a modern shark looks like. It was six feet long, with a streamlined body, 5-7 gill slits, and dorsal fins. The main differences between the Cladoselache and modern sharks are the round nose shape, lack of claspers, and its jaw was inflexible and fixed to its head.
The Carboniferous Era: The Golden Age Of Sharks
The Carboniferous Era began around 360 million years ago. It was during this time that sharks dominated the oceans. Sharks also split into many subspecies including rays, skates, and chimaeras. Sharks had incredibly diverse physiognomy during the Carboniferous age. Some of the most unique species of sharks that ever existed lived during this era. Strange species of sharks like the Stethacanthus, a shark like a flat anvil-like, spiky fin, the Eugeneodontida, a shark with a tooth whorl at the end of their bottom jaw, and the Falcatus, nickname the unicorn shark, grew a long, sharp horn on it’s head evolved during this period. During the Carboniferous Era, there were 45 different families of sharks not including rays. This was the most diverse period of sharks in Earth’s history.
The Jurassic Era: The Rise of Modern Sharks
The Jurassic Era began around 200 million years ago, during this time 12 new families of sharks appeared. These sharks were the predecessors of the sharks that exist today. During the Jurassic Era, sharks began to evolve flexible and protruding jaws so they could attack and eat larger prey. They also developed tail fins that allowed them to swim faster and more efficiently. Most sharks also developed mouths under their snout. Sharks also evolved unique traits to respond to habitat pressures like bioluminesce among deep sea sharks. One of the more unique evolutionary quirks of this era was the appearance were non-extinct horned sharks like the Hybodus.
Cretaceous Period: Recognizable Sharks
During the Cretaceous Era, 145 to 65 million years ago, many of the sharks still alive today developed. Deep sea sharks like the goblin shark or the frilled shark, originated during the Cretaceous Era. Filter feeders like the whale shark, the basking shark, and the megamouth shark first appeared. The Cretaceous was also the time period when Lamnidae sharks, sometimes referred to as white sharks, with the anatomy of what we think of sharks having today, evolved. Lamnidae are the predecessors of modern sharks like great whites, mako sharks, and bull sharks.
The Early Cenozoic Era: Enter The Megalodon
During the Cenozoic period, about 60 million years ago, the most famous prehistoric shark evolved, one that defined sharks as a ruthless, efficient, apex predators: The Megalodon. Megalodon Shark facts are incredible. The Megalodon was the biggest ocean predator to ever exist, reaching a whopping 65 feet in length and weighing over 30 tons. This terrifying predator, with 7 inch long teeth, used to eat whales. The Megalodon was not the only giant shark found in the oceans during the cenozoic era, another shark the Otodus grew to a staggering 39 feet in length, twice the length of the biggest great white sharks.
The Modern Cenozoic: Today’s Shark
Most of the sharks on the planet have developed in the Cenozoic era, except for the truly ancient sharks from the Cretaceous period. The newest shark species to enter the water is the Hammerhead Shark. Hammerhead Shark evolution only dates back about 20 million years. Currently there are around 440 species of shark swimming in our oceans, however every year scientists are finding more unique species so you never know what unique evolutionary traits we will discover next.
The Future: Uncertainty
Sharks have been on the planet for 450 million years and have survived all 5 mass extinctions. However, all 440 species of sharks are currently under threat from humans. 100 million sharks are killed every year due to human activity, and if we do not stop this brutal massacre of sharks, then they will not survive into the future. Plus if we kill off all the shark species, we will never be able to understand prehistoric sharks and learn things like more Megalodon Shark facts or what Stethacanthus did with his spiked anvil fin or why filter feeders grow so big. It would be a shame to see a successful species that has adapted the environmental changes of nearly half a billion years wiped out because of humanity’s negligence.