About 66 million years ago, a huge asteroid blasted towards Earth, wiping out three-quarters of plants and animals on the planet and heating up the world for 100,000 years. The dramatic event is most famous for killing off the dinosaurs, but how did it affect birds?
A new study, published in Current Biology, suggests that although some birds obviously did survive the asteroid, the ones reliant on trees did not. Huge forest fires would have swept across the world, so flying birds that nested in trees wouldn’t have made it through the mass-extinction event. On the other hand, their less agile ground-dwelling relatives did.
A team of scientists, led by palaeontologist Daniel Field from the University of Bath, UK, analyzed the plant fossil record. They found that just after the asteroid impact there was a great deal of charcoal from burnt down trees, along with tiny fern spores, which would have initially replaced the lost forests.
The researchers also found that many of the birds living towards the end of the dinosaurs’ reign were tree-dwelling. However, the most recent common ancestor of today’s birds probably stayed on the ground, leading the team to conclude that the first flying birds died out with the dinosaurs, and tree-dwelling behavior re-evolved later on.
Weirdly enough, birds are technically dinosaurs and originated during the Triassic Period of the Mesozoic era about 225 million years ago. Once upon a time they would have had sharp teeth, but a need to cut egg incubation time meant that this feature was lost. Exactly how they evolved to fly is often debated, but it would have allowed them to fill their own ecological niche and protect them from predators by perching up high.
“Today, birds are the most diverse and globally widespread group of terrestrial vertebrate animals – there are nearly 11,000 living species," Field said in a statement. "Only a handful of ancestral bird lineages succeeded in surviving the K-Pg mass extinction event 66 million years ago, and all of today's amazing living bird diversity can be traced to these ancient survivors."
However, molecular evolutionist Alan Cooper told Science that the real history might not be as simple as the new paper makes out. The research doesn’t necessarily show that all the world’s forests were lost, and even if they were, other pressures might have also played a role in determining which bird species survived.
Nevertheless, as co-author Regan Dunn points out, we can still learn from this mass extinction. "The end-Cretaceous event is the fifth mass extinction – we're in the sixth," she said. "It's important for us to understand what happens when you destroy an ecosystem, like with deforestation and climate change – so we can know how our actions will affect what comes after us."
