When scientist Chris Griffin found a giant bone in Zimbabwe, he knew he "was holding Africa's oldest dinosaur".

Mbiresaurus raathi¹ was a dog-sized plant-eater. This small dinosaur evolvedChanged slowly. into the largest creatures² to walk the Earth.

Around 252 million years ago, an extinction event³ wiped out 90% of life. Dinosaurs took over the world until an asteroid⁴ wiped them out 187 million years later.

Mbiresaurus raathi "shows that dinosaurs didn't start out worldwide, ruling the world from the very beginning", says Griffin. Early dinosaurs lived in the hot and wet south and came north as the climate changed.

This is "one of the most important discoveries anywhere in the world", says scientist Stephen Brusatte. But what can we learn from dinosaurs?

Very little, some argue. Around 60,000 years ago, humans developed fine stone tools. A series of advances took us from caves to cities and finally the moon.

"Dinosaurs became extinct because they didn't have a space program," wrote science fiction writer Larry Niven. Technology will solve today's problems, not history.

Not true, says expert Mary Schweitzer: "The fossil record tells us climate change is the planet's 'normal' state." Discovering five previous mass extinctionsScientists studying the fossil record have documented five major mass extinctions in the last 450 million years. helps us understand we are causing a sixth.

"The best way to look ahead is to look behind," says Schweitzer. For millions of years, dinosaurs were successful.

And they are not extinct. Some survived. The birds.

In the 1990s, a Chinese farmer found the world's first feathered dinosaur. Since then, research has confirmed that birds are dinosaurs.

"Learning the secret of flight from a bird," wrote Orville Wright, "was like learning the secret of magic." He invented the aeroplane in 1903. So maybe we have dinosaurs to thank for air flight and space travel?

Yes: Most species are extinct. If we want to survive on Earth, we must learn from the history of life.

No: Fossil hunting is fun. But it is a waste of money to dig up the past. We should be worrying about our future.

Or... Science is about discovering new things. When we look into the past, we do not know what we will find. But if we do not look, we will never find anything.

Evolved - Changed slowly.

Mass extinctions - Scientists studying the fossil record have documented five major mass extinctions in the last 450 million years.