‘We live with 10,000 species of dinosaurs today — birds are their descendants who survived’

It’s popularly believed dinosaurs went extinct after an asteroid crashed on Earth — how true is that?
■ It’s not true at all because while almost all dinosaurs did perish, including the famous ones like Tyrannosaurus and those with horns and spikes, one type survived. They had feathers, wings and could fly — these are birds. Today’s birds are dinosaurs. So, some dinosaurs survived the asteroid. Perhaps the Deccan volcanoes in India played a role. As they survived, birds diversified. There are now over 10,000 species of birds — that means over 10,000 species of dinosaurs live with us.

How did the Deccan Plateau volcanoes help?
■ Towards the end of the Cretaceous period, the last part of the age of dinosaurs, big volcanoes in India started to erupt. These were huge holes in the ground that opened and lava poured out for thousands of years, especially around when the asteroid hit.

That, of course, was the main reason most dinosaurs, along with 75% of all species, perished. Alongside, these volcanic eruptions were changing the climate and ecosystems — they too might have played a role. This was way back when India was an island — it had detached from the rest of the southern hemisphere before India collided with Asia.

You mentioned most dinosaur species were eliminated — why did one group survive?
■ I’ve written about this extensively in my new book ‘The Story of Birds’. There are some important facts here. First, there were birds before the asteroid hit — 150 million years ago, around the Jurassic period’s end, there were birds with wings made of feathers, able to fly. When the asteroid hit, there were different birds, some with teeth instead of beaks, some with big claws or long tails. Yet, only one type survived — these were the more modern-style birds, with beaks instead of teeth, small-sized, able to grow fast and fly really well. These features helped these birds survive when the asteroid hit.

That would have been chaos then, with earthquakes, wildfires, tsunamis, all the smoke from the fires and pulverised rock from the asteroid collision. All this went into the atmosphere and blocked out the sun for many years, and Earth would have been dark and cold. Trees would have perished without sunlight — so, being able to eat seeds with beaks would have helped as seeds last longer than most foods. Also, the ability to reproduce and grow fast would help, as would being able to fly very well.

After that happened, why did a tremendous variety of birds in size, colour, wings, flight abilities, etc., evolve?
■ When those few birds survived the asteroid, they’d have looked out on a largely empty world, with most species gone. So, there would have been abundant opportunities for them to evolve and do new things. They wouldn’t have had as many competitors and in such freedom, they could experiment with different ways of flying, eating diverse foods, etc. — from that came the great diversity of modern birds.

If birds are dinos, could dinosaurs also sing?
■ We don’t know — but it’s a fun thing to think about. What we do know is that some fossil birds that lived at the end of the Cretaceous era with other dinosaurs could make sounds like birds today. We know this as we actually see the voice box preserved as a fossil, the unique organ that birds have where the throat meets the lungs and allows birds to tweet, chirp and sing. So, there were birds singing during the age of dinosaurs. But whether T-Rex, Triceratops or similar dinosaurs could sing, we don’t know. We know that T-Rex wasn’t roaring as shown in the movies sometimes — its vocalisation would have been more like a crocodile.
Birds are intelligent and emotional — so, did dinosaurs have these qualities too?
■ It’s a fascinating thought. Birds are really remarkable. Most of them fly, something humans have long dreamed of doing. They bear big brains for their bodies. A parrot, for instance, easily repeats something you say while crows and ravens recognise themselves in mirrors and make tools. Many animals use tools — a cow might use a stick to scratch itself. But crows take wire or twigs and twist them into hooks to get food. This is something only humans and some other primates can do. Also, some birds have empathy. Ravens, emus and others can understand the perspective of another bird — they know it’s not all about them.

Given this, I think we can imagine dinosaurs also could have had intelligence and empathy. Mapping modern birds’ qualities onto the family tree, the prediction is the common ancestor would have also had high intelligence and empathy. Some close relatives of birds, like Velociraptors, could have had the same. Velociraptor had very large brains. So, they were probably quite intelligent.

What happened to mammals with the asteroid crash?
■ We actually had ancestors that stared down the asteroid, small, furry little creatures that were probably the size of shrews or mice. They had hair, they could keep themselves warm, they could hide easily, dig burrows, eat different foods, grow fast and reproduce quickly. Now, these mammals had been living with dinosaurs for over 150 million years. They were always small, never growing bigger than a house cat, because the dinosaurs kept them so. However, they were diverse — there were swimming mammals, climbing ones, digging ones, even gliding mammals with wings of skin that would glide overthe heads of dinosaurs. Once the asteroid wiped away big dinosaurs, mammals who survived took advantage of fewer predators and competitors — they began growing. Within 2,00,000 years, mammals the size of pigs existed. Within a million years, there were cow-sized mammals. Mammals survived and bulked themselves up, moving into some of the ecological niches the dinosaurs left behind.

Did smaller beings have an evolutionary advantage?
■ That depends on the environment you’re living in, the climate and evolutionary pressures. When it comes to surviving sudden upheavals with change, it is often good to be small because you need less food, you can grow faster — and it’s easier to hide.

You write of how, as the world warmed in the Paleocene, beings which survived the asteroid began moving across Earth — what implications does that hold for global warming today?
■ About 10 million years after the asteroid, there was a big spurt of global warming. The Iceland volcanoes started erupting. Back then, these were a lot more violent and as their lava came up, it burnt through Earth’s crust, releasing greenhouse gases like carbon dioxide and methane — yet, that did not cause a huge extinction. Rather, it unleashed waves of migration — animals could move around the poles now because the climate was so warm. So, this became an age of movement and familiar groups today, like rodents, primates and hoofed animals, spread around the world.
During this time, some mammals with hooves who lived in India went into the water, turned their hooves into flippers and started to swim — they were the ancestors of whales. Some of the most advanced and developed mammals we see today came out of this period of mass migration. That shows when environments change, there isn’t always a big extinction — different things can happen.

Professor Brusatte will be speaking at the India International Centre, Delhi, on May 21