Shark Evolution
Shark © Magnus Lundgren.

Most scientists believe that sharks came into existence around 400 million years ago (200 million years before the dinosaurs) and descended from a small leaf shaped fish that had no eyes, fins or bones. Ancestral fish evolved and diverged into the two main groups seen today; Osteichthyes (bony fish) and Chondrichthyes (cartilaginous fish).

The fossil record documents over 3,000 types of shark and their relatives, however it is likely that many more existed but disappeared without trace. After death a shark’s skeleton rots away due to it being made of cartilage instead of bone, so usually the only remains are its teeth, dermal denticles and fin spines - although from a single tooth scientists can tell what the shark fed on and even identify the species.

The fossil records of sharks are abundant and diverse. Some fossil species that lived over 150 million years ago are identical to shark, skate and ray species that exist today. One of the earliest known species is the Cladoselache, which lived about 350 million years ago, like many other early sharks their mouth was located at the front of their snout. Ancestors the Megamouth Shark (Megachasma pelagios), Frilled Shark (Chlamydoselachus anguineus), Angelshark (Squatina squatina) and devil rays still have this today, whereas most sharks have evolved a mouth under their snout.

One fossil tooth, belonging to the Megalodon Shark, was recorded at 17cm, which suggests an enormous predator as long as two buses. This species was a relative of the White Shark (Carcharodon carcharias), however Whites are much smaller with teeth about 6cm long.

Sharks have either shared or solely owned the position at the top of the marine food chain for over 400 million years. The species that briefly joined them as apex predators have consisted of massive marine reptiles such as Mosasaurs and Plesiosaurs, but sharks are the only group to have survived to modern day.

There are four periods that make up the entire history of planet Earth: 

The Precambrian

This began with the evolution of the Earth 4.6 billion years ago and is categorised by a complete lack of animal life.

Helicoprion fossil jaw © Emma Louise Nicholls.

The Paleozoic (545-250 million years ago)

The Paleozoic saw the evolution of life from single celled organisms to bony fish and sharks. The first of two major shark radiations (a rapid increase in the number of species) occurred during this time. In an age called the Carboniferous a number of sharks evolved weird and crazy appendages. None of the shark species that lived in the Paleozoic are around today, but they form the basal ancestry of modern sharks and were essentially similar in looks, diet and life habits.

Cowsharks © Sijmon De Waal.

The Mesozoic (250-65 million years ago)

Four out of the ten Paleozoic Orders survived into the Mesozoic. During the Jurassic period 12 new groups evolved during the second of the two major radiations. It was within the Jurassic that the Neoselachians (all modern shark families) and the skates and rays (Batoids) first evolved.

Hammerhead Shark © Jillian Morris.

The Cenozoic Period (65 million years ago - present day)

Hammerheads were the last of the modern shark families to evolve, and did so in the Cenozoic. It is actually very difficult to say for certain when they first appeared as their teeth are easily confused with those of another shark, but their evolution date is estimated at between 50 and 35 million years ago. Following the fall of the great marine reptiles at the end of the Mesozoic, only modern sharks and toothed whales (such as the Killer Whale) remain at the top of the food chain.

Shark evolution is an exciting and complex story that includes two major radiations and the miraculous survival of five mass extinctions, however today many species of shark, skate and ray are under threat from overfishing and other damaging human activities. Find out how you can help by visiting our Get Involved page.