All about sharks, The strange and terrifying
world of prehistoric sharks.
Since first appearing at least 420 million years ago, sharks have undergone many strange and sometimes terrifying changes to evolve into the sharks we know today.
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Interactive Timeline of shark evolution : sharks are among earth's oldest lifeforms, having appeared at least 420 million years ago - nearly 200 million years before the first dinosaurs. Trace the evolution of sharks. Pre historic sharks were really weird.
How do experts know about prehistoric sharks ??
Palaeontologists study fossilized bones to learn how creatures evolved. But sharks don’t have bones; they have cartilage, which dissolves quickly in ocean water. Luckily, after some sharks died, their bodies lay on rocks, leaving a fossilized impression on the rocks. Studying these gives good clues about shark evolution.
So, how exactly did sharks evolve over time? Some were born with features that made them better able to survive. A shark with a useful feature would pass along that feature to its offspring. Over millions of years, this happened from generation to generation. Sharks with superior features reproduced rapidly and sharks without those features died off because they could not compete successfully for food and mates.
One example of this can be found in the special way shark jaws work. Scientists believe that the first sharks with jaws that were not fused to their heads appeared about 200 million years ago. This gave them the ability to thrust their jaws forward and catch prey efficiently. Today, many sharks have this feature.
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Early sharks had smooth skin and couldn't thrust their jaw forward
When sharks first appeared, at least 420 million years ago, they were not quite like the sharks we know today. Like modern sharks, they had a skeleton made of cartilage. They had triangular fins, gills and pointed teeth. But they lacked a few key shark traits.
One of the most well-known early sharks, Cladoselache, lived 370 million years ago. Unlike today’s sharks, it could not thrust its upper jaw forward when attacking. Like other sharks of its time – and most animals – Cladoselache ’s jaw was entirely fused to its head. This restricted the size of the food it could suck in and eat. It was not until sharks evolved the ability to unhinge their upper jaw – sometime during the Jurassic period, 201 to 145 million years ago – that they started to take on larger prey, eventually growing to massive size.
Cladoselache had another odd early shark trait: smooth skin. Unlike modern sharks, which are covered in tooth-like scales called dermal denticles, Cladoselache was virtually naked. A shark’s denticles not only protect it from injury, they reduce drag in the water and strengthen the skin to provide firmer attachment for swimming muscles. But this did not seem to slow down Cladoselache; it was a high-speed predator with a keeled, crescent-shaped tail fin similar to today’s turbo-charged macho sharks.
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A weird ancient shark looked like it had a hairbrush sticking out of its back.
Stethacanthus – a fast-swimming shark that lived around 320 million years ago – was a very odd-looking fish. It had an enormous, flat-topped dorsal fin bristling with enlarged scales; together, they gave Stethacanthus the appearance of having a hairbrush sticking out of its back. Even the top of its head was covered in bristle-toothed scales.
But what were these for? Perhaps they were defensive, the brushy fin and cranial bristles looking like the jaws of a far larger predator. It seems more likely, though, that they played some role in courtship rituals. Females may have chosen males with the biggest dorsal brush, or perhaps males used these to push against one another in vigorous battles over mating rights.
Stethacanthus is also one of the earliest examples of a shark with dermal denticles – tooth like scales that cover the skin. These scales prevent injury, reduce drag in the water and strengthen the skin to provide firmer attachment for swimming muscles. Earlier sharks had smooth skin, but all modern sharks have denticles like Stethacanthus.
But what were these for? Perhaps they were defensive, the brushy fin and cranial bristles looking like the jaws of a far larger predator. It seems more likely, though, that they played some role in courtship rituals. Females may have chosen males with the biggest dorsal brush, or perhaps males used these to push against one another in vigorous battles over mating rights.
Stethacanthus is also one of the earliest examples of a shark with dermal denticles – tooth like scales that cover the skin. These scales prevent injury, reduce drag in the water and strengthen the skin to provide firmer attachment for swimming muscles. Earlier sharks had smooth skin, but all modern sharks have denticles like Stethacanthus.
Megalodon was one of the largest predators ever lived on earth.
WHAT DID MEGALODON LOOK LIKE ?
No one’s really sure what megalodon looked like – all that remains of this prehistoric monster are teeth and a few vertebrae. But these allow palaeontologists to take a fairly educated guess. Tap or click on hotspots for more information.
A SUPER-SIZED SAND TIGER?
Some palaeontologists cast doubt on the whole idea of comparing Megalodon to great whites. Megalodon evolved from an earlier giant shark called Otodus, which had teeth like a sand tiger. Could this mean that Megalodon might have looked more like a sand tiger shark on steroids? We’ll never know for sure.
NO LONGER LIVING
While it’s frighteningly fun to imagine that Megalodon might still be out there, scientists are positive that this monster shark is no longer around. The fossil record for Megalodon extends from 15.9 to 2.6 million years ago. Our ancient cousin, Homo habilis, coexisted with Megalodon but probably never laid eyes on it.
THE GREAT WHITE MODEL
It makes sense to use the great white as a model for what Megalodon might have looked like – their teeth are close to the same shape. Most scientists imagine Megalodon as a super-sized great white with a few subtle differences
It’s commonly accepted that Megalodon had proportionally larger pectoral fins than a great white. Its air plane-like fins helped support the weight of the shark’s enormous jaws and robust head
BODY SIZE
How massive was Megalodon? Scientists have been debating this for years. Early models placed its length at around 80 feet, but careful analysis of how tooth enamel height compares to body length in great whites (which scientists use as a model for Megalodon) brought this ancient nightmare’s size down to half that.
It was later discovered that this comparison only holds true for great whites up to 16 feet in length, after which their tooth enamel stops growing. If Megalodon teeth worked the same way, how large this massive shark got is truly anyone’s guess. Scientists now conservatively estimate that it grew to 52 feet, with a possible maximum length of 59 feet, and that it weighed 40 tons or more
Many of us have seen Megalodon jaws hanging in museums, but these are replicas; their fossilized jaws have never been found. Scientists reconstruct what this ancient shark’s jaws might have looked like by using great white jaws as a model. The conclusion: Megalodon had absolutely massive, over-sized jaws that spanned at least 6 to 7 feet across. It’s calculated that its jaws packed a 24,400 to 41,000-pound bite force – the strongest of any animal ever recorded
Hundreds of Megalodon tooth fossils have been found, dating all the way back to the 1600s. Most are 3 to 5 inches, with some reaching over 7 inches in length. Megalodon teeth look like huge,puffed up, blackish triangles with a bulbous root. They have a rough exterior that gets smoother at the tooth’s finely serrated edges (there are about 50 serrations per inch along the edges).
Some scientists think that Megalodon may have had a broader, more domed head than a great white. Its snout may have been shorter and more blunted, and it’s possible that its eyes were set a bit lower on its head compared to the white shark
ANYONE'S GUESS
In 1996, scientists Michael Gottfried, Leonard Compagno, and S. Curtis Bowman discovered that tooth enamel height actually stops growing when a white shark reaches about 16 feet, so it’s not an effective model for the largest individuals. If Megalodon teeth worked the same way, how large this massive shark got is truly anyone’s guess
CALCULATING SIZE
Ichthyologist John E. Randall discovered a correlation between the great white’s largest upper teeth and the height of its jaws, as well as the enamel height of its teeth and its body length. Using these ratios as a model, Megalodon teeth can reveal the size of the shark’s massive jaws and the length of its body
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Fossil sharks' teeth can tell us a surprising amount of information about prehistoric sharks, from where they lived to what they ate to how large they were. Shark’s teeth are the most abundant type of shark fossil, in part because sharks shed thousands throughout their lifetime, and in part because they fossilize comparatively easily.
To become a fossil, a tooth must be buried in sediment rather quickly. This protects it from weathering and abrasion, and limits its exposure to oxygen and bacteria – the agents of decay. In a process called permineralization, water seeps through sediments and over the tooth, depositing minerals in the tooth’s pores. This slow process, which can take many thousands of years, transforms the tooth into a fossil.
Why don’t we find shark skeletons in the fossil record? We do find bits and pieces, but rarely. A shark’s skeleton is made of cartilage, which does not mineralize to the extent that bone does and breaks down much quicker. Shark scales and vertebrae are more commonly found – both are prone to calcification – but in nowhere near the same numbers as teeth.Luckily, sharks' teeth can tell us lots about the past. A recent discovery, for example, indicates that sharks may be able to adapt to climate change. Thousands of sharks' teeth dating back to the Eocene (56 to 34 million years ago) were found in the Canadian Arctic. An analysis showed that these sharks (extinct sand tigers) lived in a relatively warm Arctic sea with very low salinity – practically freshwater. Meanwhile, their modern-day relatives prefer salt water. This finding suggests that at least some sharks could potentially adapt to the rising temperatures and decreased salinity that scientists expect to see in the Arctic of the future.
A group of very tough sharks that first appeared around 300 million years ago miraculously survived the world’s biggest extinction event (the Permian-Triassic) to live and flourish alongside the dinosaurs. These devil-horned sharks were called hybodonts.
Hybodonts had wickedly sharp teeth and head spikes that gave them a devilish appearance. Their hook-shaped head spikes may have served as defense, but just as likely could have existed to “turn on” members of the opposite sex, much like deer antlers.
They also had a blunt head, a curious ridge between the eyes and a well-developed spine on both the front and back of their dorsal fins.
Hybodonts were similar to today’s bullheads, and, like bullheads, they had different kinds of teeth – sharp canines at the front of their mouths for biting and flat molars at the sides for grinding. They spent their days hunting small fish, squid and other sea life along shallow coastal waters. They disappeared with the dinosaurs around 65 million years ago.
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SOME PREHISTORIC SHARKS SPORTED DEVILISH HEAD SPIKES
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LONG-SNOUTED BABY SHARKS THRIVED IN THE OLDEST KNOWN SHARK NURSERY
They were called bandringa. These tiny, 4- to 6-inch-long baby sharks lived 310 million years ago along a tropical coastline in what is now northeastern Illinois. The paleontologists who recently discovered the nursery – the earliest-known shark nursery containing fossils of both young sharks and eggs – are Lauren Sallan and Michael Coates of the University of Michigan.
“Bandringa had a head entirely covered in large spines, a long paddle-like rostrum (snout) with electroreceptors, and one of the earliest jaws capable of protruding and suction feeding,” Sallan told Discovery News. Resembling a modern-day sawfish or paddlefish, bandringas are among the earliest closest relatives of all modern sharks.
What’s also interesting about this find is that it’s the earliest-known example of shark migration and “the earliest evidence for segregation, meaning that juveniles and adults were living in different locations,” Sallan said. Adult bandringas, which could grow to 10 feet in length, migrated downstream from freshwater swamps in what is now Ohio and Pennsylvania to the prehistoric coastline to spawn.
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A GODZILLA-LIKE SHARK TERRORIZED THE ANCIENT OCEANS OF PRESENT-DAY NEW MEXICO
The Godzilla shark, which lived 300 million years ago, was a monster compared to other fish of its time. Measuring seven to nine feet in length, it dwarfed the other fish of its locality, most of which were just shy of seven inches on average, with the largest not quite a foot and a half.
In describing the shark to Discovery News, independent palaeontologist John Paul-Hodnett said it possessed a number of Godzilla-like physical features. Like Godzilla’s back spines, its dorsal fin spines were huge compared to the rest of its body. It had broad, short, sharp teeth like Godzilla, and unlike the long, needle-like teeth of other sharks of the time period. Its body was covered in coarse dermal denticles, giving it almost a reptilian look and feel.
And it was simply huge compared to other creatures found at the locality – an ancient sea in what is today the Monzano Mountains east of Albuquerque, New Mexico. It remains unclear whether Godzilla shark, which belonged to a genus of Carboniferous sharks called Ctenacanths, destroyed any ancient fish cities during its reign of terror.
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ANCIENT SHARK POOP CAN TELL US A LOT ABOUT PREHISTORIC SHARKS
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MEGALODON, THE LARGEST SHARK THAT EVER LIVED, FED ON PREHISTORIC WHALES
The king of all sharks, Megalodon, first appeared 15.9 million years ago. One of the largest and most powerful predators in vertebrate history, Megalodon specialized in eating whales and other large sea creatures. Over the years, many fossilized whale bones have been found with signs of bite marks from teeth that match Megalodon ’s massive choppers, which could grow to over 7 inches in length.
Recent findings are shedding light on Megalodon ’s whale hunting strategies. In the late 1990 s, palaeontologist Dr. Bretton Kent examined the remains of a 30-foot long prehistoric baleen whale that was attacked by a Megalodon, discovering that the “monster shark” was far more aggressive in its attack style than the great white.
Megalodon ’s attack focused on the tough bony portions of its prey, such as the shoulders, front flippers, rib cage and upper spine, which great whites tend to avoid. Its teeth were large and robust and its jaws were massive; together, they packed a 24,400 to 41,000-pound bite force – the strongest ever recorded. While great whites prefer to hit their victims from below and then retreat while they bleed out, Megalodon clamped down and crushed its victim’s bones and the delicate organs harboured within. An ancient whale – its rib cage pulverized and its heart and lungs ruptured from the powerful bite – would die quickly from its injuries.
But this was not Megalodon ’s only attack strategy. Fossil evidence shows a variety of hunting techniques, from ripping apart and biting off fins in order to immobilize prey, to attacking small whales from below, perhaps similarly to the Polaris attacks displayed by the great whites of South Africa.
When it was not chowing down on whales, Megalodon also fed on seals, sea lions, giant sea turtles, sea cows, dolphins, porpoises, and other large creatures before going extinct 2.6 million years ago.
A group of very tough sharks that first appeared around 300 million years ago miraculously survived the world’s biggest extinction event (the Permian-Triassic) to live and flourish alongside the dinosaurs. These devil-horned sharks were called hybodonts.
Hybodonts had wickedly sharp teeth and head spikes that gave them a devilish appearance. Their hook-shaped head spikes may have served as defence, but just as likely could have existed to “turn on” members of the opposite sex, much like deer antlers.
They also had a blunt head, a curious ridge between the eyes and a well-developed spine on both the front and back of their dorsal fins.
Hybodonts were similar to today’s bullheads, and, like bullheads, they had different kinds of teeth – sharp canines at the front of their mouths for biting and flat molars at the sides for grinding. They spent their days hunting small fish, squid and other sea life along shallow coastal waters. They disappeared with the dinosaurs around 65 million years ago.
They were called bandringa. These tiny, 4- to 6-inch-long baby sharks lived 310 million years ago along a tropical coastline in what is now north eastern Illinois. The palaeontologists who recently discovered the nursery – the earliest-known shark nursery containing fossils of both young sharks and eggs – are Lauren Sallan and Michael Coates of the University of Michigan.
“Bandringa had a head entirely covered in large spines, a long paddle-like rostrum (snout) with electro-receptors, and one of the earliest jaws capable of protruding and suction feeding,” Sallan told Discovery News. Resembling a modern-day saw fish or paddle fish, bandringas are among the earliest closest relatives of all modern sharks.
What’s also interesting about this find is that it’s the earliest-known example of shark migration and “the earliest evidence for segregation, meaning that juveniles and adults were living in different locations,” Sallan said. Adult bandringas, which could grow to 10 feet in length, migrated downstream from freshwater swamps in what is now Ohio and Pennsylvania to the prehistoric coastline to spawn.
The 70 million-year-old fossilized poop of a baby Squalicorax. Several tiny turtle vertebrae were found inside.
Yes, sharks poop, and scientists study that poop to learn a wealth of information about sharks including what they eat and what lives inside them.
A 70 million-year-old baby shark dropping recently revealed a wealth of information to palaeontologists. The pint-sized predator had eaten a newborn turtle and then died, perhaps unable to digest the shell. The baby shark was likely a Squalicorax kaupi, or crow shark, meaning it could have grown to 16 feet in length had it survived. The turtle was a freshwater species, suggesting that the newborn shark emerged from a pupping ground in a tidal estuary, where the ocean meets inland river systems.
An even older piece of shark poop recently revealed that intestinal parasites have been plaguing animals for far longer than previously thought. The fossilized dung, dated to 270 million years ago, contained a cluster of 93 oval-shaped tapeworm eggs. These pre date other known examples of intestinal parasites in vertebrates by 140 million years.
