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Aug 31

Big Question: Why did the dinosaurs die out?

For 160 million years they walked the Earth. They were the largest land animals that have ever lived. And, thanks to the number of movies, documentaries, books and television shows featuring them, they have captivated us like no other prehistoric animals. They are, of course, the dinosaurs.

But the reign of the dinosaurs ended rather abruptly 65 million years ago, at the end of the Cretaceous Period. There are no fossils records to indicate that any dinosaurs lived beyond this point and they certainly aren’t alive today (with the exception of their direct descendants, the birds). Obviously, something quite catastrophic must have wiped them all out.

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Model of Allosaurus
Photo: Jakub Halun

There have been numerous theories to explain their sudden disappearance. These range from ultra-violent hurricanes that blotted out the sun, to showers of deadly particles from space that caused fatal cancers in the dinosaurs’ bodies. Some people have even suggested that aliens abducted them all. Biochemist Ernest Baldwin theorised in 1964 that because plants containing laxative oils had become increasingly rare 65 million years ago, herbivorous dinosaurs died of constipation. The carnivorous dinosaurs then starved to death because they had no prey left. Understandably, few people listened.

The most prevalent theory, one that is accepted by the majority of scientists today, is that by the end of the Cretaceous Period, the planet was already very sick. As the moving continents broke apart, the landscape changed and volcanic activity was rife. The atmosphere in certain parts of the world was thick with poisonous gases. Smaller dinosaurs were killed by the low-lying fumes.

Then, from space, it came. An asteroid plunged from the skies and crashed into the sea near the Yutacan Peninsula in modern-day Mexico, with 10,000 times the destructive force of all the nuclear weapons that have ever been built. The area immediately surrounding the impact site would have been rendered lifeless in milliseconds due to the incredible heat and shockwaves. Massive fires would have spread around the globe; earthquakes would have created vast chasms; tidal waves over a kilometre high would have crashed over the land, engulfing entire islands and drowning anything in their path. Immense clouds of dust would have risen into the air and not only caused killer storms and acid rain, but would have also blotted out the sun for years.

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Artist’s rendition of an asteroid impact
Photo: Fredrik

From the Ashes

It is still unclear as to whether dinosaurs, like contemporary reptiles, were ectothermic (cold-blooded) or whether they could generate their own heat. Nevertheless, it is very likely that the dinosaurs suffered immensely due to a lack of sun. If they were unable to maintain their body temperature effectively, they would have had a hard time warming up, catching food or even controlling bodily processes. Within a relatively short period of time, all non-avian dinosaurs had gone forever.

It wasn’t just the dinosaurs that were affected either. This great extinction event also heralded the end of the other great reptiles – the flying pterosaurs and swimming plesiosaurs – and prehistoric animals such as the ammonites. In all, around 75% or more of all animal species on Earth vanished.

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The Chicxulub Crater on the Yucatan Peninsula, Mexico, is the most likely site where the asteroid struck Earth 65 million years ago
Picture: NASA/JPL-Caltech

But from the ashes came the survivors. Mammals, birds and smaller reptiles, having lower food requirements than the giant dinosaurs, and being able to hide and escape nasty conditions much easier, survived. When the dust finally cleared, the great reptilian predators had gone and the Age of the Dinosaurs was over. With so many niches left open to occupy, the other animals were able to diversify and flourish. The birds made a brief bid for supremacy, growing into towering flightless monsters, but in the end it was the mammals who rose to dominance and took over the planet.

We may sometimes fantasize about bringing dinosaurs back to life, but we should remember that if the asteroid hadn’t killed them off 65 million years ago, it is likely that they would have continued ruling for many more millions of year – perhaps even until the present day. Mammals would still be occupying fringe ecological niches, which means primates – and ourselves – would never have evolved. We owe our very existence to a mass extinction.

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