How Long Have Sharks Existed? Older Than Trees and Dinosaurs

When did the first sharks appear?

Sharks have skeletons of cartilage, which rarely fossilizes, so their early history is pieced together mainly from scales, teeth and spines. The story begins with tiny tooth-like scales, similar to the dermal denticles on modern shark skin, found in rocks about 450 million years old. They belonged to early cartilaginous fish, the group that includes sharks, rays and chimaeras.

By the Silurian period, about 440 million years ago, fish related to sharks already had jaws and teeth. Some of the oldest were the acanthodians, or “spiny sharks”, small fish with spines in front of their fins that are now thought to sit near the base of the shark family tree.

The oldest shark-like fish known from more than scattered pieces is Doliodus, from rocks in New Brunswick, Canada, about 400 million years old. A 2003 study described a specimen preserving its teeth, jaws, skull and parts of its fins, showing a mix of shark-like and spiny-shark features.

Older than trees and dinosaurs

The age of sharks is easiest to grasp by comparing it with other milestones in the history of life:

Shark relatives were swimming in the seas some 60 million years before the first forests and around 200 million years before the first dinosaurs.

Early shark relatives

The seas of the Devonian period, often called the Age of Fishes, held some of the most famous early sharks. Cladoselache, known from beautifully preserved fossils in the Cleveland Shale of Ohio, reached about 1–2 m (3–6.5 ft) and had a streamlined body and a deeply forked tail, much like a modern fast-swimming shark. Some fossils even show traces of muscle, kidneys and the remains of its last meals.

The following Carboniferous period, about 359–299 million years ago, is sometimes called the golden age of sharks because shark-like fish became so varied. Stethacanthus males carried a strange, flat-topped crest covered in denticles on their back, shaped like an anvil or ironing board. Other groups had spiral-shaped tooth whorls or long, whip-like spines.

These early forms were not members of today’s shark groups. They were relatives on side branches of the family tree, most of which later died out.

Surviving mass extinctions

Life on Earth has passed through five great mass extinctions, and the shark lineage came through all of them, although many individual shark groups did not:

• End-Ordovician, about 445 million years ago, when shark relatives were just appearing.
• Late Devonian, about 372–359 million years ago, which wiped out many armored fish and opened space for sharks.
• End-Permian, about 252 million years ago, the worst of all, which killed most species in the sea.
• End-Triassic, about 201 million years ago.
• End-Cretaceous, 66 million years ago, which ended the non-bird dinosaurs and the hybodonts, a group of shark-like fish that had thrived for more than 200 million years.

Each time, some sharks survived and their descendants spread into the roles left empty.

When did modern sharks evolve?

All living sharks belong to a group called Selachii. The earliest confirmed members appear in the Early Jurassic, about 200 million years ago, although some scientists think the group may have begun earlier. During the Jurassic and Cretaceous, the main modern groups, from carpet sharks and dogfish to mackerel sharks and ground sharks, spread through the oceans. How many species exist today is explained in How many species of shark are there?

Many living species are much younger. The great white shark evolved about 5–6 million years ago from an extinct shark with smooth-edged teeth, and shared the oceans for a time with megalodon, which died out about 3.6 million years ago, as explained in Is megalodon still alive? The Greenland shark is thought to have split from its closest relatives only about 1–2 million years ago, even though individual Greenland sharks may live for centuries.

Are sharks living fossils?

Sharks are sometimes described as living fossils that have barely changed in 400 million years. That is a myth. Early shark-like fish looked and lived quite differently from modern sharks, and most of today’s species and families evolved within the last 100–200 million years.

What has lasted is the basic shark design: a streamlined body, a skeleton of light cartilage, rows of replaceable teeth and skin covered in denticles. That design has proved so successful that sharks have filled almost every part of the ocean, from coral reefs to the deep sea. Why the skeleton is made of cartilage is explained in Do sharks have bones?