Dinosaurs

This is the Earth as it looked about 250 million years ago. Most land is combined in one large supercontinent — Pangea. Around this time, some catastrophic event wipes out about 90 percent of the planet's species. This mass extinction event marks the beginning of a new geological period — the Triassic period. It also creates an opportunity for the few species that survived to spread and develop.

This is how, about 245 million years ago, a new group of animals evolves from reptiles — the dinosaurs. The earliest dinosaurs move around on their two hind legs positioned directly underneath their bodies. This characteristic distinguishes them from other reptiles, such as lizards or crocodiles, which have four legs extending to the side. Over time, the landmasses of Pangea separate into different continents and the climate changes. The dinosaurs adapt to new conditions, diversify, and evolve into hundreds of different species.

This major increase in dinosaur species occurs about 200 million years ago, at the beginning of the Jurassic period. Dinosaurs become the dominant animals on land! Dinosaurs can generally be divided into two groups, or orders. Dinosaurs in the first group have bird-like hips, with the pubic bone pointed down and back toward the tail. They are called Ornithischia.

Most dinosaurs in this group are plant-eaters — herbivores. Some, such as Stegosaurus, move around on four legs. Others, such as Heterodontosaurus, stand more upright and walk on two legs. The other major group of dinosaurs have reptile-like hips, with the pubic bone pointing down and forward. They are called Saurischia.

Among them are meat-eating — carnivorous — theropod dinosaurs that can run swiftly on two legs. Some, such as Velociraptors, are not much larger than modern-day turkeys, others, such as the fearsome Tyrannosaurus Rex reach the size of a bus. This group also includes sauropods — large long-necked herbivorous dinosaurs, such as Brachiosaurus and Argentinosaurus. Reaching over 30 metres in length, sauropods are the largest animals that ever walked the Earth. Not all dinosaurs exist together in the same time and space.

For example, Stegosaurus had already been extinct for approximately 80 million years before Tyrannosaurus first appeared. In fact, Stegosaurus and Tyrannosaurus are separated by more time than Tyrannosaurus and you! But why aren’t there any dinosaurs today? About 65 million years ago, at the end of the Cretaceous period, some catastrophic event occurred that abruptly changed the climate… Scientists have different theories about what happened then. Some claim a giant asteroid hit the Earth, causing clouds of dust to cover the sky and the sun.

Others think that the climate change was caused by volcanic activity. Whatever the cause, it led to a mass extinction of dinosaurs. Yet, that cataclysm wasn’t the definite end of the dinosaurs. Quite some time before the mass extinction, around 150 million years ago at the end of the Jurassic period, another group of dinosaurs evolved. These dinosaurs shared many similarities with those existing before — they had similar bones, tissues, skeletons, and even claws.

But they had one feature that set them apart: they could fly. They were the first birds! These small, avian dinosaurs somehow survived the mass extinction and continued evolving into birds as we know them now. We know about the dinosaurs thanks to remains preserved in rock as fossil records, and the scientists called palaeontologists who study them. Fossils, and the locations where they are found, give palaeontologists many clues.

These clues help us understand the fascinating world of long-extinct species. However, although fossilised remains allow palaeontologists to learn much about dinosaurs and other animals that lived alongside them, many mysteries remain.