How did the crocodiles survive the asteroid that killed the dinosaurs? – Éamonn, 5 years old, Western Australia
Hey Éamonn! This is a good question, and one that many researchers have asked.
There are two main reasons. First, crocodiles can live for a very long time without food. Second, they lived in places least affected when the asteroid hit Earth.
When the asteroid hit Earth
About 66 million years ago, dinosaurs ruled Earth. But then a massive asteroid, more than 9 kilometers wide, crashed into the shallow sea near present-day Mexico.
The explosion from this was so huge that it led to global earthquakes, tidal waves, bush fires and even toxic rain.
The asteroid also hit one of the worst places imaginable, where the rocks could easily be “exploded” (or evaporated). This threw huge amounts of dust up into the sky, blocked the Sun out for many months and sent the Earth into a long, dark and icy winter.
Without sunlight, the green plants died, followed by the herbivores that ate them to survive, and the carnivores that ate the herbivores.
Read more: Curious children: What effect did the asteroid that wiped out the dinosaurs have on plants and trees?
Scientists believe that three-quarters of all the different kinds (species) of animals on Earth were extinct – including most dinosaurs.
But some managed to survive for a number of reasons.
An important group of dinosaurs sailed through, aided by their ability to fly and find food in distant places. Their feathers protected them from the cold, and their beaks allowed them to eat buried seeds found near dead plants.
Incredibly, these dinosaur survivors are still with us today. We call them birds!
Read more: How small birds evolved from giant meats that ate dinosaurs
Crocodiles had some keys to survival
Crocodiles were another group that famously survived the asteroid. It is clear that they can not fly, do not have feathers and do not eat seeds! But they had other secrets to success.
First, crocodile bodies use very little energy. They lie around a lot, breathe slowly and even have a very slow heartbeat. This is how they can hold their breath underwater for more than an hour.
It also means they can go without food for months, and sometimes more than a year. This would have been very useful when food (such as other animals) became difficult to find once the asteroid hit.
Dinosaurs, on the other hand, were generally more active, which means that they needed more energy – especially meat eaters such as Velociraptor. Without food, they would have died quickly.
Crocodiles also lived in places where it did not make much difference to lose green plants. Think of a forest or a meadow (where many dinosaurs lived): if the plants die, all the animals that need them die, too, including the carnivores that are not left without food.
But crocodile survivors mostly lived in places like rivers, lakes and coasts. The animals that live in these places do not need green plants that much. Dead plants and animal material are washed in from the surrounding land, which are eaten by tiny creatures, which are then eaten by larger creatures including crocodiles.
So unlike dinosaurs that live on earth, crocodiles in a river would not have starved as soon as the green plants died.
The ancestors of our mammals also survived
A similar reason helps explain why human ancestors also survived the asteroid impact. It was the small mammals that lived near the end of the age of the dinosaurs that eventually gave rise to all the different kinds of mammals today (including humans).
It was mostly small, rat-like things buzzing around in the dead leaf litter on the ground, eating insects and worms. These tiny creatures were not dependent on living green plants, but on dead leaves and bark that fell from the trees or were blown and washed in from elsewhere.
So like the crocodiles, our little ancestors survived the asteroid, in part because they were not heavily dependent on living plants. One good thing too: these lucky survivors are the reason you and I are here today!