Mass extinction that wiped out the dinosaurs 66 million years ago allowed SHARKS to thrive

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A mass extinction that wiped out the dinosaurs 66 million years ago meant that sharks could thrive. Researchers think the loss of apex predators was one of the reasons for a profound increase in shark biodiversity (artist


A mass extinction that wiped out the dinosaurs 66 million years ago allowed sharks to thrive, new research has shown.

Sharks are one of the major animal groups to survive the Cretaceous-Palaeogene mass extinction.

However, a new study into hundreds of fossilised shark teeth has revealed the species not only survived – but flourished after this devastating event.

Researchers believe the loss of apex predators was one of the reasons for a profound increase in shark biodiversity.

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A mass extinction that wiped out the dinosaurs 66 million years ago meant that sharks could thrive. Researchers think the loss of apex predators was one of the reasons for a profound increase in shark biodiversity (artist's impression)

A mass extinction that wiped out the dinosaurs 66 million years ago meant that sharks could thrive. Researchers think the loss of apex predators was one of the reasons for a profound increase in shark biodiversity (artist’s impression)

Much like several other vertebrate groups during the Cretaceous period (142-66 million years ago), shark diversity looked very different from today.

At the time, mackerel sharks (lamniformes) were the dominant order of sharks in the sea.

Mackerel sharks includes great white, mako sharks, salmon sharks, basking sharks and thresher sharks.

This is in contrast with today, where ground sharks (carcharhiniformes) are the most diverse shark group on the planet, with species numbering in the 200s.

Ground sharks includes a host of hugely common species of sharks, including catsharks, hammerhead sharks and swellsharks.

‘Carcharhiniforms are the most common shark group today and it would seem that the initial steps towards this dominance started approximately 66 million years ago,’ said project leader and Uppsala University doctoral student Mohamad Bazzi.

Researchers explored variations in tooth shape in ground sharks and mackerel sharks. 

‘Unlike other vertebrates, the cartilaginous skeletons of sharks do not easily fossilise and so our knowledge of these fishes is largely limited to the thousands of isolated teeth they shed throughout their lives,’ said Mr Bazzi.

‘Fortunately, shark teeth can tell us a lot about their biology, including information about diet, which can shed light on the mechanisms behind their extinction and survival.’ 

Before the mass extinction event, mackerel sharks (lamniformes) were the dominant order of sharks in the sea. Mackerel sharks includes great white (stock image), mako sharks, salmon sharks, basking sharks and thresher sharks

Before the mass extinction event, mackerel sharks (lamniformes) were the dominant order of sharks in the sea. Mackerel sharks includes great white (stock image), mako sharks, salmon sharks, basking sharks and thresher sharks

Before the mass extinction event, mackerel sharks (lamniformes) were the dominant order of sharks in the sea. Mackerel sharks includes great white (stock image), mako sharks, salmon sharks, basking sharks and thresher sharks

Now ground sharks (carcharhiniformes) are the most diverse shark group living today, with more than 200 different species. This order includes a number of common sharks such as catsharks, hammerhead  sharks  (stock image) and swellsharks

Now ground sharks (carcharhiniformes) are the most diverse shark group living today, with more than 200 different species. This order includes a number of common sharks such as catsharks, hammerhead  sharks  (stock image) and swellsharks

Now ground sharks (carcharhiniformes) are the most diverse shark group living today, with more than 200 different species. This order includes a number of common sharks such as catsharks, hammerhead sharks  (stock image) and swellsharks

Evidence suggests there was a selective extinction of lamniforms and a subsequent proliferation of carcharhiniforms in the immediate aftermath of the extinction.

The mechanisms that triggered these changes is still not known but researchers think that availability in food would have played an important role.

The Cretaceous–Paleogene extinction saw major losses in marine reptiles and cephalopods, including squids, with bony fish species only thriving post-extinction. 

In addition, it is likely the loss of apex predators, such as lamniforms and marine reptiles, also benefited certain species of shark.

The mass extinction was caused when the planet endured a period of global warming that lasted for 100,000 years, triggered by a cataclysmic asteroid impact.

Known as the Chicxulub asteroid, the collision released billions of tons of carbon dioxide into the atmosphere, which caused the temperature of the Earth to increase by five degrees Celsius (nine degrees Fahrenheit).

‘By studying their teeth, we are able to get a glimpse at the lives of extinct sharks,’ said Dr. Campione.

He said that ‘by understanding the mechanisms that have shaped their evolution in the past, perhaps we can provide some insights into how to mitigate further losses in current ecosystems.’

Approximately 50 per cent of the shark species in the International Union for Conservation of Nature (IUCN) are considered to be either endangered, threatened, or near-threatened.

Mr Bazzi believes further research is needed to understand the diversity patterns of other shark groups, along with the relationship between diet and tooth morphology. 

This finding is reported this week in Current Biology. 

HOW SHARKS EARNED THEIR RUTHLESS REPUTATION 

Sharks are the most efficient predators on earth and have long terrified humans.

Their basic design has never really changed over the course of 200million years and they are considered to be complex and intelligent.

Their teeth are fear factor number one, with the great white’s teeth growing up to two-and-a-half inches in length.

Their prey are impaled on the pointed teeth of the lower jaw where they saw away sections of the flesh. The serrated edges of the teeth help with this process.

Their teeth are brittle and are constantly breaking off but are also constantly regrowing and on average there are 15 rows of teeth present in the mouth at one time.

Sharks are the most efficient predators on earth. Their basic design has never really changed over the course of 200million years

Sharks are the most efficient predators on earth. Their basic design has never really changed over the course of 200million years

Sharks are the most efficient predators on earth. Their basic design has never really changed over the course of 200million years

Their speed is fear factor number two. 

They are very fast in the water compared to humans with the mako shark able to reach an incredible 60mph in bursts.

The great white can reach speeds of 25mph. 

By comparison, 5mph is the fastest a human being can reach.

A shark’s power and size terrifies us, too.   

The great white shark can grow up to 20 feet and while it has no particular taste for humans even an exploratory bite is enough to cut a man in half.

Most sharks release a human after its first bite but sometimes, that’s all it take to kill a person.   

However, sharks have far more reason to be afraid of humans. We kill up to a million of them a year, often just cutting off their fins to make into soup and throwing the rest of the shark back into the water, where it starves or drowns. 

 

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