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Today, the biggest amphibian alive is this creature – the Chinese giant salamander. It breathes partly through its skin which has these long flaps on it, which absorbs oxygen from the water… but also breathes air. It was learning to breathe, something we all take for granted.

Giant Salamander learning to breathe
Giant Salamander

It’s going to come up, and as it does, it snatches a gulp of air, blows a few bubbles… and sinks down again. It’s jaw acts as a pump, forcing air down into the body. Here, oxygen is absorbed into the bloodstream from two inflatable sacks with permeable walls – lungs. Because they are enclosed inside the body, they don’t dry out.

As happens to the gills of fish, if they are out of the water.

The lungs it uses are just simple pouches coming from the back of the throat. But nonetheless, they were the first kind of lungs that animals had. The forerunners of the air-breathing organs that all of us land-living vertebrates now have.

From their origins, around 365 million years ago, the amphibians took on many different forms. Over 7,000 species now live in a variety of habitats on land and in water. They include salamanders… frogs… and newts.

But two things tie the amphibians to water. First – their skins are moist and if they dry out, they die. And secondly – their eggs, like this frog spawn, are covered in nothing more than jelly.

However, they have to be laid in water or at the very least, in moist conditions. And until the vertebrates could solve those two problems, they would not be able to colonise the dry parts of the land.

Learning to Breathe

Then, a group of pioneers appeared with an amazing new feature to their bodies. We can find evidence for this next step by looking at animals that can survive far from water today.

Tree Dragon
Tree Dragon

This little creature is a lizard. They call it in these parts a Tree Dragon. And its body is very much the same shape as an amphibian. Long body with a backbone and two pairs of limbs. But there’s one crucial difference between an animal like this and an amphibian. Its skin is not moist, it’s dry.

We can see what has changed by putting the two types of skin under the microscope. The skin of an amphibian is smooth with living cells visible on the surface. A lizard’s skin is much rougher because it contains large amounts of keratin – a protein similar to that from which our own fingernails are formed. Keratin-filled cells dry out and layer up to form scales. This creates a barrier, sealing water inside the body. We humans have inherited this keratin barrier in our skin, allowing us to maintain up to 70% of our bodies as water.

Animals with this body plan became a huge success. They evolved into a great number of species big and small. We call them reptiles.

But the reptiles still had to overcome a second challenge – how to lay their eggs out of water.

I have come to Lufeng, in southern China, to see evidence gathered by local scientists of the ingenious solution.

Reptile Eggs

These eggs were laid by a reptile, and as you might imagine, a pretty big one at that. The first reptilian eggs almost certainly had a leathery covering, rather like those a turtle lays today. But these eggs are different, they have a hard covering – a shell. And you can see where the weight of the sand that eventually covered them and fossilised them bore down upon them, they crushed that shell, but the pieces are still in place.

From examining modern reptile eggs, we know that this shell must have been made of hard calcium carbonate and it must have supported another fibrous membrane. Together, they made the egg water-tight. And that meant that the animals that laid them no longer had to go back to the water to lay their eggs, as all amphibians had to do. Instead, they could go to the driest part of the land and breed and nest and lay their eggs.

So all the dry land was open to them. Learning to Breathe had been a critical step in the transition to land.

The amphibians had spearheaded the move to land. Now, their descendants, the reptiles, were able to establish themselves in its driest parts. Over 9,500 species now inhabit our planet. But the limbs that helped the vertebrates emerged from the water began to present problems when it came to walking efficiently on dry land. Because they projected sideways, it took a lot of effort to hold their bodies off the ground. Then around 230 million years ago, one set of reptiles developed an amazing solution.

These eggs were laid by an animal belonging to the most successful of all reptile groups, the group that dominated the world for 100 million years – the dinosaurs.

More than 150 different species of dinosaur have been found in the rocks of China alone, and over 1,000 worldwide. And they too depended on a crucial advance. A radical modification of the bone that connects the leg to the body – the hip.

Lufengosaurus

This is Lufengosaurus, a plant-eater. This demonstrated how learning to breathe was not the only adaptation needed to live on land.

Lufengosaurus
Lufengosaurus

The early reptiles had legs which splayed out from either side of the body and left the body very close to the ground. But a change in the shape of the hips of the dinosaurs enabled them to bring their hind legs underneath the body and so, lift them up and give them greater freedom of movement. And some of them, including Lufengosaurus, were able to support the entire weight of the body on the hind legs.

This new hip, along with sturdier leg joints, allowed the dinosaurs to take longer strides… and support heavier bodies. They became the largest animals that have ever lived on land. But this new way of walking was also the first step on the road to an even more radical evolutionary advance.

It was from this group of two-legged dinosaurs that there came a truly astonishing development that we are only just beginning to understand, and that was to lift the vertebrates to a completely new level.

Learning to Breathe with the Giant Salamander