Sharks, 450 million years ago till today

This 2014 video says about itself:

Wherein we take an adventure into the deep oceans of history in pursuit of fossilized sharks.

From the BBC:

The epic history of sharks

There are many strange sharks but their ancestors were even weirder and more wonderful than those swimming today

By Lucy Jones

3 October 2015

When you imagine a shark, you may think of a torpedo-shaped, streamlined creature with a prominent dorsal fin, a large mouth ringed by sharp, triangular teeth and a crescent-shaped tail. Jaws, basically.

Actually, the shark group of fish are widely varied. The Epaulette shark (Hemiscyllium ocellatum) can walk on land, the frilled shark (Chlamydoselachus anguineus) is flatter-bellied, adapted to hunt in the deep-sea, the tasselled wobbegong (Eurcrossorhinus dasypogon) is a carpet shark that resembles an old patterned rug and the goblin shark (Mitsukurina owstoni) is eel-like with a long dagger-shaped snout.

These are just a handful of over 500 species of shark that we know about today, each well-adapted to its particular environment.

Yet in the past, there were many more: fossil records suggest more than 3,000 types of shark and their relatives existed at one time. And some of the ancestors of modern sharks were even weirder and more wonderful than those swimming today.

Their long history starts in the late Silurian period, about 450 million years ago. It was a time when sea levels were high and coral reefs began to form. The Earth’s climate was warm and stable. Molluscs, crinoids and trilobites were some of the only living creatures on the Earth before scorpions and centipedes appeared on the land.

Around this time, sharks too appeared, evidenced by the oldest known shark scales found in Siberian deposits.

Jawed and bony fish began to diversify, including the evolution of a group of fish called acanthodians, or “spiny sharks”. These extinct fish looked like small sharks but had varying numbers of fins.

“It appears that sharks arose from within those,” says Charlie Underwood of Birkbeck University of London, UK. “Where they end and sharks begin is quite up for debate. Certainly we know that some of these acanthodians have teeth that formed in a very similar way to sharks. The teeth will grow on the inside of the mouth and move forward as they get bigger, in a sort of conveyor belt. Among these are the earliest sharks.”

Fast forward 50 million years to the Early Devonian, a warm and arid time on Earth when forests spread across the land, seed-bearing plants first appeared and the planet underwent great geological change.

This is when we have the first remains of shark teeth, from the Leonodus shark. These teeth are both small (4mm) and two-pronged, but they offer few clues as to what the Leonodus shark actually looked like. They are similar to the teeth of another shark called Xenacanthus that appeared millions of years later in the Late Devonian, leading to speculation that Leonodus, like Xenacanthus, lived in freshwater.

It may seem that teeth are not much to go by, but everything we think we know about shark evolution is from the teeth, says Lisa Whitenack of Allegheny College in Pennsylvania, US. From teeth, she says, we can learn about what environment the shark lived in, what they ate and how they are related to other sharks.

But we have to wait until 380 million years ago for the next clue to shark evolution. That comes from the braincase of Antarctilamna, a so-called lamnid shark from Antarctica. Its head, fin, spines and teeth suggest that it was eel-like.

There’s a reason the Devonian period is referred to as the ‘Age of Fishes‘. It was the time when they diversified greatly. A skeleton of the now extinct shark Cladoselache, shows just how much. It was very different from its eel-like ancestors. It was a 2m-long, torpedo-shaped shark with equal-sized dorsal fins, a short stout spine in the front, five fill slits and large eyes. It took its prey tail-first, indicating it could easily outswim its meals.

At this time, a school-bus sized group of fish called Dunkleosteus, also swam the seas. These were giant, heavily-armoured fish and may have competed for similar prey. This could have been just the trigger sharks needed to evolve further. Other armour-plated fish existed too, but it was early sharks that seemed to have something that allowed them to thrive, while these other giants died out.

Enter the golden age of sharks, 360 million years ago during the Carboniferous period. The largest predators of the sea at this time were the Chondrichthyans (cartilage fish). They had their skeletal jaws and tough scaly skin to thank for that. The enamel on their teeth was also frequently replaced.

This group included rays (close relatives of sharks), skates and a bizarre branch called the chimaeras, which featured species such as ratfish, ghost sharks and spook fish. It was within this last group, the chimaeras, that extremely weird and wonderful sharks appeared, says Underwood. “By the Carboniferous period, the majority of shark-like things are on the chimaeras branch, rather than the branch towards modern sharks.”

Prehistoric sharks certainly looked much stranger than the modern sharks we share the planet with today, even weirder than the Port Jackson, with its strange patterning and smoothed, numerous fins.

This video is called Port Jackson Sharks (Heterodontus portusjacksoni ), 4 young sharks chilling out on the sand, Sydney, Australia.

The Stethacanthus, for example, had an anvil-shaped dorsal fin on its back. “No one really knows what it used it for,” says Christopher Bird, of the National Oceanography Centre, Southampton, UK and Shark Devocean blog. It is one of many evolutionary mysteries in the shark world.

Another was the spiral-shaped tooth structure, called a tooth whorl, of the Helicoprion. These were dinner-plate sized and likely sat at the tip of the lower jaw. Some of these tooth spirals were 40cm across.

“As they grow and move into the mouth position, rather than falling out, the teeth just stay stuck to each other,” explains Underwood. “The shark doesn’t lose teeth as they move outside the mouth. So you end up with the bottom lower jaw having a big circular blade sticking out and behind that… crushing teeth. It’s a very strange arrangement.”

These bizarre traits aside, ancient sharks actually had the same basic features as the sharks we know today.

More innovation occurred at the start of the Jurassic period, 213 million years ago, when 12 new groups evolved. Sharks with flexible jaws started to appear. This meant they could feed on things that were bigger than themselves, says Bird. “They were able to exploit the newly emerging habitats as the world was changing.”

Their protruding jaws came to good use. They could eat, crunch or suck prey into their mouths. “Sharks in the Jurassic period often had teeth with a flat-ridged surface to make it easier to crunch on crunchy things,” says Whitenack.

As environments changed, sharks evolved different features. A tail fin allowed sharks to swim faster for long distances to pursue prey. Most sharks evolved a mouth under their snout, although a few species have mouths at the front of their snouts such as the frilled shark and angel shark.

Sharks were certainly tenacious. The creatures that thrived during this period survived right into the Cretaceous, often defined by its end. Sixty-five million years ago most of the dinosaurs were wiped out. Many other animals died too but sharks lived on.

And why wouldn’t they? They had already survived four other catastrophic mass extinctions. Their bodies were clearly well adapted to survive.

What’s more, they could exploit the fact that so many other creatures were wiped out. It was during these “recovery stages following historic mass extinctions” that the biggest number of new species appeared, says Bird.

Following the asteroid that wiped out the dinosaurs, for example, there was a second wave of deep-sea sharks. “The sharks are able to recolonise the water. We start seeing the cookie-cutter sharks and lantern sharks move in after this post-crisis event,” says Bird.

These also exploited new habitats following extinction events. They even managed to survive during times when the ocean lost its oxygen – including one such event in the Cretaceous period, when many other, larger, species died out. As a refuge, sharks moved deeper underwater, says Bird. And while there, they had another cunning trick. Some evolved the ability to glow in the dark.

The end of the Cretaceous gave sharks the opportunity to flourish. Not all survivors were successful though, including one giant of the sea, once thought to be a direct relative of the great white shark.

About 16 million years ago the Carcharodon megalodon first appeared. It could grow up to 16.8m and weighed 25 tonnes. Its mouth would gape open an impressive 2m, showing its 15cm-long teeth, perfect for eating everything else big in the ocean. It made the great white shark look like a goldfish in comparison.

We don’t know why the megalodon went extinct. One idea is that climate change disrupted the availability of prey. It was big, so needed to eat a lot. Any tiny change could therefore have threatened its survival. It’s likely that many factors combined to cause this giant to disappear two million years ago.

Other survivors from the Cretaceous lived on to become the sharks we know today. Hammerhead sharks for example, are among the most recent to appear in the fossil record and are assumed to be one of the last modern shark orders to evolve.

Their t-shaped heads increase lift as the sharks swim through the water, allowing them to make sharp turns. It also helps them sense more of their environment.

And we now have greater insight into how their strange-shaped heads evolved. Genetic techniques allow us to peer back in time at the evolution of modern-day sharks. In one such experiment in 2010, scientists looked at the DNA of eight species of hammerhead to build a genetic family tree going back thousands, possibly even millions, of generations.

Our study indicates the big hammerheads probably evolved into smaller hammerheads, and that smaller hammerheads evolved independently twice,” said Andrew Martin of the University of Colorado at Boulder, at the time of the study.

“As the sharks became smaller, they may have begun investing more energy into reproductive activities instead of growth.”

Recently, it has become clear that we may not even know how many sharks live in the ocean. An elusive shark called the megamouth (Megachasma pelagios), was only discovered several decades ago. In 1976 a US research vessel off the coast of the Hawaiian island of Oahu hauled up a shark nearly 5m in length, with a great fleshy mouth surrounding broad jaws.

ince then, 49 have been found all over the world. Usually they are dead when caught but one living specimen has given scientists some idea of its environment and habits. Its soft cartilage and flabby tissue suggests a slow-steady swimmer that filter-feeds on shrimp, sea jellies and small crustaceans.

But despite new species still being discovered, the very survival of sharks is under threat. Many are endangered and their biggest threat? Us. Climate change, pollution and habitat destruction are all factors affecting their numbers.

The main threat to their survival is overfishing. Humans kill many species in large quantities for meat and fins. Several are now on a list that seeks to protect endangered species from international trade (the CITES list), and includes open-water predators such as basking, whale and great white sharks, which are caught in vast quantities for meat.

Even deep-sea sharks are vulnerable. Despite the incredible features they have evolved to help them succeed, their reproduction rate is slow. That means if any are killed, the knock-on effect is huge.

Deep-sea shark species can’t recover, explains Bird. They don’t have the potential to reproduce offspring quicker than they’re being taken out. These sharks are often targeted for their liver oil. It contains a molecule called squalene, sought after by the cosmetics industry for its moisturising properties.

The International Union for Conservation of Nature (IUCN) now estimates that a quarter of sharks and rays are threatened with extinction. Although sharks have survived several mass extinctions, the rate at which their populations are being reduced by human activity is extreme and many species are not protected. In 2014, scientists said improved management of fisheries and trade is “urgently needed” to promote population recovery.

If their rate of decline continues, the future of sharks is uncertain. “We’re a new predator in the ocean,” says Bird. Sharks were once top predator but “we’re decimating their populations. One day, they may not be able to bounce back and recover.”

Common smoothhound shark on Texel island beach

This video from Jersey says about itself:

Common smooth hound (Mustelus mustelus)

19 July 2015

Chantelle Marie De Gruchy very kindly sent in this video of a Smooth Hound that she saw whilst diving St. Catherine’s breakwater.

The smooth hound is a species of shark found throughout the British Isles which can reach 4 foot in size! They typically eat small crustaceans and molluscs but occasionally take small fish.

Chantelle is currently studying for her master’s degree in Marine Environmental Management at the University of York.

Translated from Ecomare museum on Texel island in the Netherlands today:

Shark on the beach – 22-09-2015

A special find on the beach of De Cocksdorp on Texel. There was a common smoothhound on the sand. The female had been dead for a while when she washed up. The eyes were out and there was a really fishy smell. Yet Ecomare has kept the animal; it is not every day that a shark washes up on a Dutch beach. In recent years, there seem to be again more sharks in the Wadden Sea.


The last thirty years the number of common smoothhound sharks along the Dutch coast has increased. Other shark species at the same time have gone down. This shark species can get quite large, up to 1.65 meters. The shark near De Cocksdorp was 80 centimeters. Smoothhound sharks have flat molars and are harmless to people. They live close to the coast. Usually they swim close to the sea floor where they look for crabs, shellfish and fish. They occur in the Northeast Atlantic Ocean and thus the North Sea and Wadden Sea. Along the Dutch coast they are rare.

Sharks in the Netherlands

In the North Sea you can find several species of sharks. The small-spotted catshark is the most common. Besides common smoothhound sharks also school sharks live there. Spiny dogfish is seen in some years as well. You can even encounter basking sharks, nursehounds, porbeagle sharks and Atlantic thresher sharks in the North Sea, but these are super rare.

Save Caribbean sharks

This 26 August 2015 video was recorded in the Oceanium, the big aquarium in Rotterdam Zoo in the Netherlands. It is about marking there the start of the three years long Save Our Sharks campaign, by the Dutch Caribbean Nature Alliance.

This campaign aims to help sharks in the Caribbean to survive. There are about thirty shark species in the Caribbean.

This video is called Jonathan Bird examines one of the world’s most photographed–yet least studied–sharks, the Caribbean Reef shark.

Shark study in the Netherlands

This video says about itself:

15 April 2015

School sharks, Galeorhinus galeus, in a Fuerteventura beach (Canary Islands).

There used to be quite some sharks around the Dutch Wadden Sea islands; mainly starry smooth-hound sharks and school sharks.

However, ever since the 1970s, their numbers declined.

Recently, some fishermen say the numbers are going up again.

To see whether that is true, some shrimp fishermen will tag sharks which they catch, and release them.

Today, 28 August 2015, was supposed to be the start of this. However, the young school shark caught today was too small to tag, so it was freed without having been tagged.

School shark, too small for tagging

Basking shark off California, USA

This video from the USA says about itself:

On May 5, 2012 our whale watching boat, Manute’a, encountered a rare Basking Shark off the coast of Dana Point. The animal was estimated to be about 20 feet long. These plankton eating sharks are the second largest fish in the world; only a whale shark is bigger. Whale watchers were awestruck when this huge shark turned and swam right up next to the boat!

Shark beached on Schiermonnikoog island

This 17 August 2014 video by a diver in the Oosterschelde estuary in the Netherlands shows a common smooth-hound shark.

Translated from conservation organisation Natuurmonumenten in the Netherlands:

Friday, August 21st, 2015

In mid-August participants in the beachcombers’ excursion on Schiermonnikoog found a very special find! THe Volunteer Collective of National Park Schiermonnikoog found at beach post 5 a one meter long common smooth-hound shark. …

The eyes and a part of the gills were already gone, but otherwise the shark was still completely intact.

Big dinosaur age shark discovery

Cretaceous fossil sharks reconstruction. Credit: Frederickson et al.

From LiveScience:

20-Foot Monster Shark Once Trolled Mesozoic Seas

by Tia Ghose, Senior Writer

June 03, 2015 02:01pm ET

A giant shark the size of a two-story building prowled the shallow seas 100 million years ago, new fossils reveal.

The massive fish, Leptostyrax macrorhiza, would have been one of the largest predators of its day, and may push back scientists’ estimates of when such gigantic predatory sharks evolved, said study co-author Joseph Frederickson, a doctoral candidate in ecology and evolutionary biology at the University of Oklahoma.

The ancient sea monster was discovered by accident. Frederickson, who was then an undergraduate at the University of Wisconsin-Milwaukee, had started an amateur paleontology club to study novel fossil deposits. In 2009, the club took a trip to the Duck Creek Formation, just outside Fort Worth, Texas, which contains myriad marine invertebrate fossils, such as the extinct squidlike creatures known as ammonites. About 100 million years ago the area was part of a shallow sea known as the Western Interior Seaway that split North America in two and spanned from the Gulf of Mexico to the Arctic, Frederickson said.

While walking in the formation, Frederickson’s then-girlfriend (now wife), University of Oklahoma anthropology doctoral candidate Janessa Doucette-Frederickson, tripped over a boulder and noticed a large vertebra sticking out of the ground. Eventually, the team dug out three large vertebrae, each about 4.5 inches (11.4 centimeters) in diameter. [See Images of Ancient Monsters of the Sea]

“You can hold one in your hand,” but then nothing else will fit, Frederickson told Live Science.

The vertebrae had stacks of lines called lamellae around the outside, suggesting the bones once belonged to a broad scientific classification of sharks called lamniformes that includes sand tiger sharks, great white sharks, goblin sharks and others, Frederickson said.

After poring over the literature, Frederickson found a description of a similar shark vertebra that was unearthed in 1997 in the Kiowa Shale in Kansas, which also dates to about 100 million years ago. That vertebra came from a shark that was up to 32 feet (9.8 meters) long.

By comparing the new vertebra with the one from Kansas, the team concluded the Texas shark was likely the same species as the Kansas specimen. The Texan could have been at least 20.3 feet (6.2 m) long, though that is a conservative estimate, Frederickson said. (Still, the Texas shark would have been no match for the biggest shark that ever lived, the 60-foot-long, or 18 m, Megalodon.)

By analyzing similar ecosystems from the Mesozoic Era, the team concluded the sharks in both Texas and Kansas were probably Leptostyrax macrorhiza. Previously, the only fossils from Leptostyrax that paleontologists had found were teeth, making it hard to gauge the shark’s true size. The new study, which was published today (June 3) in the journal PLOS ONE, suggests this creature was much bigger than previously thought, Frederickson said.

Still, it’s not certain the new vertebrae belonged to Leptostyrax, said Kenshu Shimada, a paleobiologist at DePaul University in Chicago, who unearthed the 1997 shark vertebra.

“It is also entirely possible that they may belong to an extinct shark with very small teeth so far not recognized in the present fossil record,” Shimada, who was not involved in the current study, told Live Science. “For example, some of the largest modern-day sharks are plankton-feeding forms with minute teeth, such as the whale shark, basking shark and megamouth shark.”

Either way, the new finds change the picture of the Early Cretaceous seas.

Previously, researchers thought the only truly massive predators of the day were the fearsome pliosaurs, long-necked, long-snouted relatives to modern-day lizards that could grow to nearly 40 feet (12 m) in length. Now, it seems the oceans were teeming with enough life to support at least two top predators, Frederickson said.

As for the ancient shark’s feeding habits, they might resemble those of modern great white sharks, who “eat whatever fits in their mouth,” Frederickson said. If these ancient sea monsters were similar, they might have fed on large fish, baby pliosaurs, marine reptiles and even full-grown pliosaurs that they scavenged, Frederickson said.