The first dinosaurs

The story

A word invented in 1842

The word “dinosaur” is less than two hundred years old. It was invented in 1842 by an English anatomist, Richard Owen, who was studying some big fossil bones found in England. He realised that they belonged to a group of reptiles not yet recognised and called it Dinosauria, from the Greek for “terrible lizards”. Before then the bones of these animals had been found several times, but nobody knew what they were. Some thought they were dragons or giants.

Dinosaurs ruled the planet for a very long time: from the Triassic, about 230 million years ago, until the end of the Cretaceous, 66 million years ago. That is more than 160 million years, an enormous time compared with the roughly 300,000 years of our species. But the beginning of their story was much more modest than you might think.

Valley of the Moon

The oldest certain dinosaur fossils come from South America. One of the most important places is Ischigualasto Provincial Park in Argentina, also called the Valley of the Moon for its landscape of red, grey and purple rocks carved by the wind. Here there is a sequence of Triassic layers, about 231 million years old, which has yielded some of the oldest dinosaurs known. Another place is the state of Rio Grande do Sul in Brazil.

Among the most important fossils are Herrerasaurus, a predator 4 to 6 metres long, and Eoraptor, discovered in 1991 by an expedition led by the American palaeontologist Paul Sereno. Eoraptor, whose name means “dawn thief”, was about a metre long, light, walked on two legs and had teeth that differed from one another, perhaps because it ate a bit of everything: small animals but also plants. Scientists think the first dinosaurs were like that: not giants, but agile animals of medium or small size.

There are also clues to older forms. In Tanzania Nyasasaurus has been found, about 243 million years old, which some scholars consider the oldest dinosaur or a close relative of one, but the bones are few and the debate is open. That is why the date of the “first dinosaur” is not fixed: the timeline says about 230 million years ago, following the most certain fossils.

What is a dinosaur?

Not all ancient reptiles were dinosaurs. Pterosaurs, ichthyosaurs, plesiosaurs and Dimetrodon were different animals. Dinosaurs had one particular feature: their legs were set beneath the body, in an upright position, as in us or in a horse, and not out to the sides, as in a lizard or a crocodile. This made it easier to run and to breathe while walking. In 1887 another English scientist, Harry Seeley, divided the dinosaurs into two big groups according to the shape of the hip: the saurischians, with a “lizard” hip, and the ornithischians, with a “bird” hip. Paradoxically, birds descend from the saurischians.

A slow rise

For the first 30 million years the dinosaurs were not the masters of the world. In the Triassic other reptiles dominated, relatives of the crocodiles, which were bigger and more varied, and there were also the first mammals and many large amphibians. Dinosaurs were one group among many. Their moment came around 201 million years ago, when another mass extinction, at the end of the Triassic, removed many of the competitors. From then on dinosaurs spread and became dominant, giving rise in the Jurassic to the long-necked giants and in the Cretaceous to predators such as Tyrannosaurus.

Their success is perhaps explained by a combination of features: upright legs, high speed, good breathing and an ability to adapt. But scholars do not yet have a complete picture: luck and circumstances counted for a great deal.