The earliest shark-like teeth we have come from an Early Devonian (410-million-year-old) fossil belonging to an ancient fish called Doliodus problematicus. Described as the 'least shark-like shark', it is thought to have risen from within a group of fish known as acanthodians or spiny sharks.
During the Carboniferous Period, sharks went through a period of diversification resulting in the evolution of many new forms. Many of these became extinct during the Permian with the remaining sharks undergoing adaptive radiation during the Jurassic, when the skates and rays first appeared.
Cladoselache is regarded as the first "true shark". It lived 380 million years ago and it still retained a few characteristics of its fishy ancestors. It had a fish-like head, seven gills instead of five like most sharks, and its body was longer and less muscular than the sharks we see today.
They uncovered the partial skull, including the brain case, of a 410-million-year-old fish. It is a new species, which they named Minjinia turgenensis, and belongs to a broad group of fish called 'placoderms', out of which sharks and all other 'jawed vertebrates' – animals with backbones and mobile jaws – evolved.
Scientists believe that the earliest sharks were small and elongated, shaped almost like a torpedo, with a very similar dorsal and caudal (tail) fin to today's sharks [22.01].
Sharks are older than trees and dinosaurs
The earliest evidence of shark fossils dates back as far as 450 million years, which means these creatures have been around at least 90 million years before trees and 190 million years before dinosaurs.
The Middle Ages were a dark period for the knowledge of sharks and science in general, says Bottaro. Superstition seemed to take over from the more studied approach taken by Pliny and Aristotle, and sharks were depicted as sea monsters or devils.
Sharks have survived many mass extinction during their presence of 450 million years on Earth. Scientists believe that their ability to repair damaged DNA has helped them survive over the years. Their presence on the planet over millions of years have earned them the title of living fossil.
Cyanobacteria
What is this? Cyanobacteria are the oldest existing species in the world. These bacteria are believed to be the Earth's oldest known life form.
The earliest shark-like teeth we have come from an Early Devonian (410-million-year-old) fossil belonging to an ancient fish called Doliodus problematicus. Described as the 'least shark-like shark', it is thought to have risen from within a group of fish known as acanthodians or spiny sharks.
Sharks are older than trees and dinosaurs
The earliest evidence of shark fossils dates back as far as 450 million years, which means these creatures have been around at least 90 million years before trees and 190 million years before dinosaurs.
Sharks have roamed the Earth's oceans for more than 400 million years. In the process, the animals have survived five mass extinction events, including the one that wiped out the dinosaurs. This latter extinction event occurred around 66 million years ago, marking the end of the Cretaceous period.
Young epaulette sharks are able to walk in and out of the water using their paddle-shaped fins. It is an evolution researchers describe as “breaking all the rules of survival.”
The Silurian Era: The First Sharks
450 million years ago, during the Silurian period, sharks first began developing as a unique species. During that time, the ocean was filled with a variety of bony fish. One of these fish, the Acanthodian, was the very first ancestor of the modern shark.
Frilled shark
It is a shark though; it's just 150 million years old and hasn't evolved much. Of all the prehistoric creatures that still exist, the frilled shark might be one of the weirdest marine species ever!
Today there are two living coelacanth species, known as Latimeria, which have basically remained unchanged over the past 100 million years. Horseshoe crabs are ancient creatures that first appeared at least 480 million years ago during the Ordovician Period and don't appear to have changed much since.
Today's crocodiles, which in scientific terms are part of the Crocodilia Order, first appeared about 95 million years ago. That was 30 million years before dinosaurs went extinct.
Tardigrades have been around a long time.
Fossils date their existence on Earth to more than 500 million years ago. This means tardigrades have survived the planet's last five mass extinction events. They owe their longevity to some special characteristics.
Without sharks as apex predators, the entire ocean ecosystem could fall out of balance. They not only maintain the species below them in the food chain, but also indirectly maintain seagrass and coral reef habitats.
The cooling of the planet may have contributed to the extinction of the megalodon in a number of ways. As the adult sharks were dependent on tropical waters, the drop in ocean temperatures likely resulted in a significant loss of habitat.
Sharks have been known to attack humans when they are confused or curious. If a shark sees a human splashing in the water, it may try to investigate, leading to an accidental attack. Still, sharks have more to fear from humans than we do of them.
But despite being potentially such an easy meal, sharks are really not that interested in hunting humans. “They generally just ignore people. I think if people knew how frequently they were in water with sharks, they would probably be surprised.”
Whale shark: The biggest specimen ever reliably measured was 18.8 metres or nearly 62 feet long – that's bigger than a school bus!