Sharks are some of the Earth’s oldest lifeforms, outlasting almost any other creature that’s ever lived. But does that make them dinosaurs? How have they survived for so long? How have they evolved?
We’re here to answer all your burning questions and give you a timeline of this extraordinary ocean creature’s past, present and future.
How long have sharks been on Earth?
Sharks have swum in the oceans for almost 450 million years, which makes them far older than dinosaurs, trees and even the stars in the skies.
That’s not all, though – they’ve also lived through every major mass-extinction event and the ocean temperature changes that came with each one. To put that into perspective, the ancestry of sharks dates back more than 200 million years before the earliest known dinosaur, making their evolution one of nature’s most enduring success stories.
Are sharks dinosaurs?
Despite being around before the dinosaurs, the answer is no – sharks aren’t classed as dinosaurs. In fact, they’re not even the same type of creatures since sharks are fish and the dinosaurs were reptiles.
How have sharks evolved?
With such a long history, it should come as no surprise that sharks have evolved over the years to keep up with environmental changes. So, from the Silurian period to now, let’s explore all the developments these animals have gone through.
The Silurian period
Fossil scales are the earliest known evidence of sharks, dating back 450 million years to the Silurian period. This is when they’re thought to have begun developing and diversifying in the Earth’s oceans.
Acanthodians are one of the fish families with fossils dating back the furthest, but while some refer to them as ‘spiny sharks’, others categorise them as a different type of fish, separate from sharks. These belong to a group called chondrichthyans, which includes modern sharks and rays. Little is known about the shark species from this period, and fossilised remains of these spiny and scaled creatures are being continuously studied to learn more.
The Devonian period
The Devonian period occurred around 400 million years ago, and in the later stages of this period, Earth experienced its first major mass extinction. Sharks are thought to have survived by diving deeper underwater, where temperatures were less affected. This meant they could continue developing.
Cladoselache is recorded to be one of the earliest known sharks, with fossil records dating to this period. The species is thought to have gone extinct around 250 million years ago, most likely because of climate change or lowering sea levels. However, some believe that the population decreased because of the faster development of other shark species.
The Carboniferous period
Getting its name from the Carboniferous coal produced by bark-bearing trees growing large swamp forests around the world, the Carboniferous period began approximately 359 million years ago. Aside from this, it’s also known as the Golden Age of Sharks, when they began to develop and diversify in shape and size. During this time, their jaws and teeth became more like the shark features we know in modern species today.
The waters saw strange species developing, such as the Stethacanthus altonensis. Males of this species had a unique first dorsal fin shaped almost like an ironing board, which was thought to be used to court females for mating.
The Jurassic period
The Jurassic period might have begun around 200 million years ago, but the lineage of some shark species can still be traced back to this period. Modern sharks and rays developed at this time, with most fossil records showing sharks with fins, teeth and jaws like the species still in our oceans today.
Hexanchiformes (sixgill sharks) were one of the earliest shark families to develop in the Jurassic period. Thanks to their flexible, protruding jaws, allowing them to eat bigger prey and the ability to swim faster with their adapted fins, shark populations grew rapidly.
The Cretaceous Period
Beginning around 145 million years ago, the Cretaceous period is notably marked by the fifth mass extinction. Known for warm ocean temperatures and a large asteroid strike toward the end of the period, fossil records show that some of the largest shark species that once lived in the oceans became extinct at this time.
However, the temperature shift also shaped their evolution to help them survive in different environments. The biggest shift is in their appearance, since their pectoral fins and muscle mass adapted based on where they are in the world and the types of water they swim in.
The Cenozoic period
Starting 65 million years ago and leading us to the present day, this period saw the development of many modern sharks, including great whites and tiger sharks. Hammerhead sharks also evolved during this time, and it’s thought that they’re the most recent development in shark evolution.
The megalodon, otherwise known as the biggest ocean predator, might have gone extinct around 3 million years ago, but it was still a dominant shark species for much of this period. Growing up to 18 metres in length and living mostly in tropical waters, the main reason they’re thought to have become extinct is down to ocean temperatures dropping.
What does the future of sharks look like?
Sadly, even though they’ve survived so many huge changes on the planet over the last 400 million years, many sharks are on the endangered list because of overfishing, habitat loss and climate change. Species like the smooth Hammerhead shark and the Japanese angelshark, the dumb gulper shark and the daggernose shark are all on the IUCN endangered list at different severities.
But there are still ways we can help protect this species and make sure they thrive in the future. As a vital part of the marine ecosystem, staying educated about shark habitats and behaviours and dispelling myths about them being as dangerous as the media often portrays them can help. We can also support shark charities who are working to stop overfishing, conserve endangered species and protect the oceans. Whether you volunteer or donate, any support can make a difference.
Visit some of the oldest creatures on Earth at Blue Reef Portsmouth
No need to take your binoculars to the beach in hopes of spotting these ancient creatures – we have several shark species you can see up close here at Blue Reef Portsmouth. From the small spotted catshark to the bull huss, you can learn plenty more about the different characteristics of sharks and how they’ve survived so long on your next visit. Book your tickets here and start planning your day!