Dinosaurs — The Rulers of the Earth

Dinosaurs first appeared on Earth about 230 million years ago, during a period called the Triassic. They were not immediately the dominant animals on the planet — at first, they were small, fast creatures living alongside many other types of reptile. But over millions of years, they evolved into an extraordinary variety of shapes and sizes, and eventually became the most successful group of land animals the Earth has ever seen.

Dinosaurs ruled the Earth for about 165 million years. To understand how long that is, consider this: modern humans have existed for only about 300,000 years. If the entire time dinosaurs existed were compressed into one hour, the entire history of humanity would take up less than one second.

During their time on Earth, dinosaurs evolved into an incredible range of species. Scientists have identified more than 1,000 different species so far, and new ones are being discovered every year — on average, a new dinosaur species is named about every two weeks. Some were enormous. The Argentinosaurus may have weighed up to 70 tonnes — as heavy as 12 elephants. The Patagotitan was so long that it would have stretched across a football pitch. Others were tiny — the Microraptor was about the size of a pigeon.

Dinosaurs lived on every continent, including Antarctica — which was much warmer 100 million years ago than it is today. They occupied almost every ecological role — predators, herbivores, scavengers, and even fliers. They were, by any measure, one of evolution's greatest success stories.

If you picture a dinosaur in your mind, you probably imagine a grey or green scaly reptile — like the ones in the Jurassic Park films. But scientists now know that this image is mostly wrong. Modern research has completely changed our understanding of what dinosaurs actually looked like.

One of the biggest discoveries of recent decades is that many dinosaurs had feathers. Not just small dinosaurs — even some large predators like Velociraptor were covered in feathers. Scientists know this because beautifully preserved fossils found in China show the clear impressions of feathers in the rock. Some dinosaurs were brightly coloured, with red, brown, black, and even iridescent feathers — more like modern birds than the grey lizards of popular imagination.

This connection between dinosaurs and birds is now well established in science. Birds are not just related to dinosaurs — they are dinosaurs. Specifically, they are the only surviving group of theropod dinosaurs, which also included Tyrannosaurus rex and Velociraptor. When you see a sparrow or a chicken, you are looking at a living dinosaur.

Scientists have also learned that many dinosaurs were much more active and intelligent than previously thought. Some species hunted in packs, suggesting complex social behaviour. Others built nests and cared for their young, much like modern birds. Brain scans of dinosaur skulls suggest that some species — particularly the smaller predators — were quite intelligent for reptiles, with large brain-to-body ratios comparable to modern birds.

T. rex, the most famous dinosaur of all, has been particularly transformed by new research. Scientists now believe it may have had lips covering its teeth, that it could not actually roar (it probably made deep booming sounds), and that juvenile T. rex may have been covered in fluffy feathers before developing scales as adults.

About 66 million years ago, a rock from space about 12 kilometres wide — roughly the size of a city — slammed into what is now the coast of Mexico at a speed of about 72,000 kilometres per hour. The impact was one of the most violent events in the history of our planet, and it changed the course of life on Earth forever.

The asteroid hit with the force of billions of nuclear bombs. It created a crater more than 180 kilometres wide and 20 kilometres deep. The impact sent enormous amounts of rock, dust, and gas into the atmosphere, blocking sunlight for months or possibly years. Without sunlight, plants could not grow. Without plants, herbivorous animals starved. Without herbivores, the predators that ate them also starved. The food chain collapsed from the bottom up.

About 75% of all species on Earth went extinct, including all non-bird dinosaurs. It was one of the five mass extinction events in Earth's history, and it is the most recent one. The crater, called the Chicxulub crater, was only discovered in the 1970s — it is buried under layers of rock and partly hidden beneath the ocean.

Not everything died, however. Small mammals, some birds, reptiles like crocodiles and turtles, and many fish and insects survived. With the dinosaurs gone, mammals — which had been small, nocturnal creatures living in the shadow of the dinosaurs for millions of years — suddenly had the opportunity to grow larger, spread into new habitats, and diversify. Over the following millions of years, mammals evolved into the incredible variety we see today — including, eventually, humans. In a very real sense, we owe our existence to that asteroid.

The study of dinosaurs — called palaeontology — is one of the most exciting and rapidly changing areas of science. New technologies are allowing scientists to discover things about dinosaurs that would have been impossible just twenty years ago.

CT scanning — the same technology used in hospitals — allows scientists to look inside dinosaur skulls without damaging them. This has revealed the size and shape of dinosaur brains, the structure of their inner ears (which tells us about their hearing and balance), and even the pathways of blood vessels and nerves. From these scans, scientists can estimate how intelligent a dinosaur was, how well it could see and hear, and how fast it could move.

Chemical analysis of fossils can now reveal what dinosaurs ate, how fast they grew, and even what colour they were. Tiny structures called melanosomes, preserved in fossilised feathers, contain information about pigment — allowing scientists to reconstruct the colours of some dinosaurs with remarkable accuracy.

New dinosaur fossils are being found at a faster rate than ever before. China, Argentina, and Mongolia are currently the richest sources of new discoveries. In Thailand, dinosaur fossils have been found in several provinces, including Kalasin and Nakhon Ratchasima. The Sirindhorn Museum in Kalasin is one of Southeast Asia's most important dinosaur research centres.

Perhaps the most exciting question in modern palaeontology is whether we could ever bring dinosaurs back to life. While the Jurassic Park scenario of extracting DNA from amber is not scientifically possible — DNA breaks down far too quickly to survive 66 million years — some scientists are exploring whether we could reverse-engineer dinosaur characteristics in modern birds, since birds carry dinosaur genes. For now, this remains science fiction. But the dinosaurs themselves were once considered impossible too — until someone found their bones in the rock and began to ask questions.