Although many people tend to think that dinosaurs were the ancient animals of the past, sharks as well as other mammals appeared quite earlier than dinosaurs. Sharks originated approximately 450 million years ago during the late Silurian. Because soft tissues of sharks did not preserve well, but the bones such as their teeth did, scientists used shark teeth as the main means to trace the evolution of sharks. Using their teeth, scientists were able to infer the food they consumed, the environment they lived in, and many other aspects alike. Current dating technology only allows scientists to date and compile a complete shark fossil record as far back as approximately 400 million years ago. Although scientists are not able to date completely back to the very origin of sharks, 400 million years is pretty good already right?
The very first fully developed shark was a species called the Leonodus shark from approximately 400 million years ago (early Devonian). The Leonodus had small two-pronged teeth that were about 4 mm. Despite being the first fully developed shark, its body resembled more of an eel than the modern day shark. Not much else is known about the Leonodus, but it is a good starting point to the evolution of sharks.
The very first fully developed shark was a species called the Leonodus shark from approximately 400 million years ago (early Devonian). The Leonodus had small two-pronged teeth that were about 4 mm. Despite being the first fully developed shark, its body resembled more of an eel than the modern day shark. Not much else is known about the Leonodus, but it is a good starting point to the evolution of sharks.
Source: "Leonodus shark" by Shark Sider
The next apparent evolution was a species called the Cladoselache shark from approximately 380 million years ago (late Devonian). The Cladoselache had dorsal fins and around 5 gill slits. One of the main differences between the Leonodus and the Cladoselache was that the latter had more of a modern day streamline shark body.
Source: "Cladoselache shark" by Shark Sider
The next step up in evolution was from approximately 360 million years ago (Carboniferous). The Carboniferous period was the period in earth's history with the most diverse sharks. Sharks split into many other species such as rays and chimaeras. This was also a time when sharks adopted interesting features that scientists are still unsure as to what the purpose of them are. For example, the Stethacanthus shark had an anvil-like fin on its back.
Source: "Stethacanthus shark" by BBC
Going from the Carboniferous period to the Jurassic period approximately 200 million years ago, there was the evolution of 12 new groups of sharks that were very similar to the sharks we see and know today. The main evolutionary features the sharks developed included a more flexible jaw for the consumption of organisms bigger than themselves and a tail fin for faster swimming in the ocean.
Following was the Cretaceous period approximately 145 million years ago when many sharks such as the goblin shark and the whale shark originated illustrating the origin of deep sea sharks and filter feeder sharks respectively. Many sharks from this period illustrated those of today.
We then arrive at the early Cenozoic period approximately 60 million years ago with the origin and existence of what was known as the Megalodon shark. The Megalodon was approximately 60 feet long and 30 tons with 7 inch long teeth. Being as big as it was, the Megalodon fed on other smaller sharks such as the great white shark. However, the Megalodon did not exist for long in earth's shark history as it suddenly became extinct. Scientists speculated that the extinction may have had to do with climate change during the Cenozoic period. Climate change could have caused smaller organisms that primarily made up the diet of the Megalodon to die out. The decrease in availability of food could have possibly driven the Megalodon to extinction.
Source: "Megalodon scale" by Shark Sider
Finally, there is the existence and evolution of modern day sharks. Many modern day sharks come from the time periods from above, but the newest shark species today is the hammerhead shark from approximately 20 million years ago. Incidentally, hammerhead sharks are what fishers tend to target today in terms of the shark fin trade industry.
Source: "Hammerhead shark" by National Geographic Kids
