Ornithological Evolution

The backboned animals had colonised the seas and invaded the land. But there was one final Habitat to explore – the skies.

Another extraordinary Chinese fossil bed is providing the missing evidence for one of the great mysteries in evolutionary science – the intriguing link between dinosaurs and birds.

Liaoning Province

I’m heading for Liaoning province to fulfil a long-held dream and see the site of these discoveries for myself.

These rocks are about 125 million years old. At that time, this part of China was tropical and the land was covered with a lot of freshwater lakes.

And in those lakes was washed sediment which formed these bands here. But every now and again, the sediment changes colour. And that is ash that was spewed out from the nearby volcano so that about that level there, there were a lot of skeletons waiting to be discovered. And when they were discovered, they revealed some sensational facts about dinosaurs, the most sensational for a very long time.

This fossil was one of the most remarkable to emerge. The two-legged dinosaur about the size of a cat. It’s been named Sinosauropteryx. Its discovery revealed an intriguing feature never seen before on a dinosaur.

Up its tail and down its back, a covering of what looks like fur. Fresh finds have revealed that a wide range of two-legged dinosaurs had skin covered by very similar hair-like filaments. But what were they for?

Professor Xu Xing

In Beijing, there are the crucial specimens that answered those questions. This is one of the world’s leading institutions in the study of dinosaur evolution. Professor Xu Xing and his colleagues have been analysing another larger specimen of Sinosauropteryx. It too retains traces, just fragments of the mysterious filaments.

Professor Xu Xing “If you look near the tail, the dark things are there near the tail, they are single filaments just like our hair, which are very, very simple.”

Xu Xing has been puzzling over their function. Together, these filaments create a covering like fur, so the most likely answer is that they served to keep these dinosaurs are warm. But detailed examination has suggested an additional and very different function.

Experts at the Institute have taken minute samples and examined them under powerful magnification. They contain intriguing structures. Some are lozenge-shaped, some spherical. Investigators identified them as melanosomes – microscopic capsules that contain pigment. They would have given the filaments on Sinosauropteryx’s tail colour.

Prof Xu Xing “Based on our analysis, you see stripes. One like white, brown, white, brown. It’s a beautiful pattern. Of course you can’t see all, that’s maybe for display or communication or…”

Do we know how it held its tail?

Prof Xu Xing “The tails definitely can move in different directions. In most cases, I would guess is up or horizontal.”

So, it’s like a ring-tailed lemur used to its tail around as a display.

Dinosaurs may have used these coloured furry bands to signal to other members of the species or to act as camouflage. But then came a discovery that suggested another far more significant function.

Anchiornis

I’ve been granted privileged access to the underground vaults in the Beijing Museum of Natural History, to look at one of the most important creatures yet to be found in the fossil beds of Liaoning.

This is an Anchiornis, a creature that’s clearly a dinosaur. It’s got powerful legs here ending with toes with sharp claws on them, and its head, which has been detached, lies here upside down but you can see the jaw, which has teeth in them. But what is spectacular about this particular specimen is the perfection of the preservation of these structures. They show that the simple filaments have developed into something far more complex. The central stalk has tiny strands branching out on either side. The filaments have become feathers.

Analysis of them has shown that the crest here on the head was a rufous red colour and the body feathers were striped black and white. These are feathers all down the legs. And looking at the density of them on the forearms here, it does look very like the wing. So the question is could this animal fly? Could this be the moment when he dinosaur became a bird? A clue to the answer could come from the environment in which it lived. At this time, this area of northern China was covered in lush forests. Animals that could climb trees would be able to collect food that was not available on the ground. They could also find safety from ground-living predators. Xu Xing and his colleagues see evidence that Anchiornis adapted to a tree-living way of life, by putting its feathers to a new use.

Professor Xu Xing “Anchiornis has some features suggesting a tree-living lifestyle. For example, you look at the Anchiornis toe, they have very curved claws. And also, they have big feathers attached to their feet. If Anchiornis is a tree-living animal, then I have good reason to believe that flight started from tree down. Which means that the birds’ ancestor can take advantage of gravity and then start their journey to the sky.”

Because Anchiornis lived high up, it could use its feathers to glide. It must have needed all the feathers growing along its front limbs, hind limbs and tail to create a large enough surface to catch the air and slow its descent.

Gliding Flight

It wasn’t capable of flapping flight but, at 160 million years old, it’s now the earliest creature we know to have used feathers to fly.

The gliding dinosaurs would eventually give rise to a whole new group of vertebrates… the birds. Over 9,000 species crowd our skies today. An astonishing evolutionary journey had enabled the vertebrates to dominate every corner of the planet.

It was a journey that began in the Cambrian seas over 500 million years ago, and that led to the development of a set of body parts that we ourselves would ultimately inherit. Jaws and a bony skeleton from the early fish… limbs and lungs from the amphibians… water-tight skin from the reptiles. By the time the birds appeared on the planet, the early pioneers of another major vertebrate group had also evolved. At first, they were tiny but they were destined eventually to dominate the Earth – they were the mammals.

Most, I dare say, were little better than snack food for the dinosaurs, but all that was about to change. A devastating meteor strike, that many believe triggered a mass extinction. We don’t know exactly what happened, but certainly, 65 million years ago, all the dinosaurs disappeared. But some of the birds and mammals survived and with the bigger dinosaurs gone, the world was up for grabs.