The rise and fall of the dinosaurs
Dinosaurs walked the Earth for an incredible 165 million years. They first appeared in the late Triassic Period, before diversifying to dominate the planet, and become the largest land animals to have ever lived.
However, 65 million years ago, the reign of the dinosaurs was to come to an abrupt end. An event so monumental occurred that it changed the shape of our planet forever. Evidence points to a giant asteroid which smashed into the Earth, leaving a crater nearly 200km wide. Such an impact would have kicked dust and debris up into the atmosphere, darkening the planet for months and could have triggered other events such as "super-acid rain", global firestorms and "mega-tsunamis".
All the dinosaurs that were living 65 million years ago went extinct. But there is one important caveat, one group – the theropod dinosaurs – found a way to live on.
The fossil that changed everything
In 1861, a palaeontologist by the name of Christian Erich Hermann von Meyer, wrote about his discovery of a single, fossilised feather at a limestone quarry near Solnhofen, Germany.
Soon after von Meyer’s find, an almost complete fossil of the animal it belonged to was discovered – that of Archaeopteryx. It was to be one of the most important fossil discoveries ever made.
On first inspection, it looked like other fossils of theropod dinosaurs of the time. But the fact clear imprints of feathers were found all around its body is what made Archaeopteryx so special. Until this time, no intermediate forms between living animals and their ancestors had been found. It supported Charles Darwin’s controversial theory of evolution and was soon declared to be an evolutionary link between dinosaurs and birds.
And you can clearly see why as here was an animal, known to have lived about 147 million years ago, that looked half-dinosaur, half-bird.
Half dinosaur, half bird
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Archaeopteryx was the first, and is still one of the best, transitional fossils to be found; clearly showing features of a modern bird and a theropod dinosaur. Take a closer look at some of these features (image copyright naturepl.com).
From dinosaur to modern bird
For a long time, Archaeopteryx stood alone – the only half-dinosaur, half-bird animal known. However, in the last twenty years a huge number of new fossils have been discovered. Some look more like dinosaurs with feathers than animals capable of taking to the sky. Others look more like birds, but with quirky features. Microraptor, for example, had four wings.
These fossils have largely convinced experts that some dinosaurs didn’t die out at all. Instead a particular group of small, agile, two-legged dinosaurs evolved into birds. But how did a group of land-loving dinosaurs take to the sky and come to look like the birds we see today?
We don’t know exactly why feathers appeared, but they are thought to have evolved from the scales of the theropod dinosaur’s reptilian skin. There are a number of reasons for having feathers other than flight and have been found in a number of dinosaurs clearly not capable of flying. Feathers can act as insulation to maintain body temperature or to keep eggs and young cool by providing shade. And much like modern male peacocks flash their tails; feathers were used for ornamentation and decoration during displays, with Epidexipteryx’s four long ribbon-like tail feathers one of the earliest examples known.
There is a bewildering range in the size and shape of modern birds’ beaks, mainly adapted for specific feeding strategies. This avian feature might have evolved to help herbivorous dinosaurs chew their food, placing less stress and strain on the skull than a jaw and teeth. The lighter weight of a beak without teeth then became useful before these dinosaurs took to the air.
Dinosaurs also began to become smaller and lighter, shifting forward their centre of gravity, shortening their tails and developing longer fore arms with each generation, leading to the crouched posture we see in living birds today. Their wrists also became more flexible as we move towards the flexed wrists of a modern bird.
Taking to the skies
Once early birds had all the features necessary for powered, or flapping, flight how did they eventually take to the skies? There are a number of popular theories, which are illustrated with modern day examples.
Legacy of the dinosaurs
The evolution of birds from their theropod dinosaur ancestors is now thought to have begun in the late Jurassic Period, which roughly spanned 200 to 145 million years ago.
The catastrophic events of 65 million years ago that wiped out the dinosaurs also caused a huge decline in primitive birds. Only a few of these early bird groups survived this mass extinction. We’re not sure what saved them but from these few surviving groups emerged the birds we see around us today.
There are now around 10,000 species of birds, making them one of the most successful and specialised groups of animals on the planet. From large flightless ostriches to tiny hummingbirds, all share an ancestry with the theropod dinosaurs of the past.
Bird or dinosaur?
Choose one of these modern birds to see what features it has in common with the 'terrible lizards'?