Facts about Prehistoric Sharks

Long before dinosaurs walked the Earth, sharks were roaming the oceans. Their legacy has been traced back at least 420 million years which is quite amazing. They have been able to evolve as needed to continue surviving.

If you have seen a live shark directly, feel lucky, because you have known one of the oldest forms of life on the planet. Sharks appeared on Earth more than 400 million years ago, and they still continue to amazing us with their features.

It is not easy to find fossils of sharks as their skeletons consist of cartilage instead of bones. While bones can be well persevered for millions of years, cartilage has a faster decomposition rate as it is a softer tissue.

Then, how do researchers and scientists know that sharks existed millions of years ago? These conclusions are possible because of their teeth. Each shark can produce up to 30,000 teeth over their life, and these teeth made of dentine and enamel does fossilize in the ocean which has lead to significant evidence of how long sharks have been around.

Scientists think that the most dramatic evolution of sharks took place during the Cretaceous period. During this time there was an abundance of food, sharks grow, and different species appeared.

Sharks appeared on Earth more than 400 million years ago.

As food sources were abundant everywhere, sharks no longer had to stay in one place. Many of them migrated to new areas to find new food sources. As they found new environments though they had to evolve to be able to survive there. In some areas, there weren’t much fish. Therefore, some species of sharks became dependent upon other prey like clams and mollusks, and others opted for plankton.

Researchers have found some fossils along with teeth that date back to the Miocene period. These indicate that some significant changes took place in the appearance of sharks in that time.

Another relevant period of evolution for sharks was around 5 million years ago known as the Pliocene period. The changes in this period were due to the shifts in water temperatures. Many species of sharks had to adapt to the colder waters of that time.

Can you imagine a prehistoric shark? Seeing them today in the graphical representations that scientist created from fossils, make us think that they look like fish, not a shark. The evolution of sharks has been long and full of unfathomable interrogations that even today we can only guess to try understanding the life they had and the way they survived.

Many prehistoric sharks are known thanks to their fossils, and here below we present 10 of them, with a brief summary:

It is the name of an extinct genus of sharks that lived during the Carboniferous period, about 360 million years ago. This carnivorous fish had a length between 0.7 and 2 meters, and their look was not far from that of modern sharks. They had a somewhat odd dorsal fin, resembling an anvil and they had a skin covered with dermal denticles.

It is believed to be migratory animals that traveled to strategic points to mate and have their offspring. Their diet consisted of fish, crustaceans, and cephalopods.

Order: Symmoriida.
Family: Stethacanthidae.

Carcharocles angustidens.
This species of prehistoric shark had large, serrated teeth and fed on penguins, fish, dolphins, and whales. It lived during the Oligocene and Miocene epochs, 22-35 million years ago.

Featuring an enormous size, it far exceeded that of the current white shark (Carcharodon carcharias). Its fossils discovered in regions of North America, South America, Europe, Africa and Oceania proved that.

Order: Lamniformes
Family: Lamnidae or Otodontidae (no agreement).
Gender: Carcharodon or Carcharocles (no agreement).

This genus of shark existed during the Cretaceous and the Paleogene periods 50 to 90 million years ago. According to fossil records, species of this genus, of medium size, were common in waters of North America, Africa, and the Middle East.

The species belonging to the Cretolamna genus fed on turtles, squid, bony fish and even other sharks. The researchers estimate that the animals had a length of 2 to 3 meters and teeth 1 or 2 centimeters long.

Order: Lamniformes
Family: Otodontidae

It is a genus of sharks that lived in the Devonian period. There is a compendium of relatively extensive information about them because their fossils have been well preserved.

They lived 400 million years ago, especially in North America. They had a fusiform body that had a length about 1.8 meters. Their mouth was on the front of the head, had spiny fins, comb crests, 5-7 gill slits, two pectoral fins, two pelvic fins and a forked tail.

They were probably agile predators and had smooth teeth, therefore instead of chewing on their prey, they swallowed it.

Order: Cladoselachiformes
Family: Cladoselachidae

Xenacanthus: They were some of the first freshwater sharks.

Another genus of sharks that inhabited the Earth from the late Devonian to the mid-Permian period, 202 million years ago. They were some of the first freshwater sharks.

Order: Xenacanthida
Family: Xenacanthidae

The members of this genus of sharks were very different from the appearance of the modern sharks. They lived in North America during the late Carboniferous period and had a round head, arched back and a single dorsal fin located at the end of the back. They were not small because they reached a length of 2 meters.

Order: Symmoriida
Family: Symmoridae

It is an extinct genus of prehistoric sharks which had six species. They appeared on Earth at the end of the Permian Period and thrived during the Triassic, Jurassic, and Cretaceous. They were probably 2 meters long and looked like many modern species. They had two dorsal fins, a small mouth and two types of teeth. The males already had claspers.

Order: Hybodontiformes
Superfamily: Hybodontoidea
Family: Hybodontidae

Megalodon: It is believed to be the largest shark that has ever existed in the oceans.

This genus of sharks that lived during the Cretaceous period had similarity to the modern goblin shark (Mitsukurina owstoni) and were in fact relatives. They were not very large. They had a length about 50-65 centimeters and had a long, flattened nose as well as a calcified spine to withstand flexion movements when swimming.

Superorder: Selachimorpha
Family: Mitsukurinidae

It was a giant shark that lived in North America during the Cretaceous period 82-100 million years ago. This shark did have a lot of resemblance to those that live now: it had a length up to 7 meters, had a fusiform body and very sharp straight teeth. He was a very feared predator that fed on bony fish, turtles, and other marine animals.

Order: Lamniformes
Family: Cretoxyrhinidae
Genre: Cretoxyrhina
Species: Cretoxyrhina mantelli

The Megalodon may not be missing from any list of prehistoric sharks. It is believed to be the largest shark that has ever existed in the oceans and lived 2-20 million years ago. It was more than 20 meters long and had about 276 large teeth in its jaws. Estimates suggest that it consumed about 2,500 kilograms of food per day.

Order: Lamniformes
Family: Lamnidae or Otodontidae
Genus: Carcharodon or Carcharocles








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