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Rise and fall of the dinosaurs contents

T. rex would not have recognised the world that the first dinosaurs lived in. In this series of articles, Dr Jo Wright explores how the dinosaurs evolved as the world around them changed.

At the dawn of the age of the dinosaurs, the world was very different. Dr Jo Wright, scientific advisor to the BBC One series Walking with Dinosaurs describes life in the late triassic, in the first of eight articles about the age of the dinosaurs.

When dinosaurs first appeared about 230 million years ago the world was very different. There were very few of the animal groups we recognise today - no mammals, no birds and no lizards. But there were some lizard-like reptiles.

What? No grass?

The difference was also apparent in the plant kingdom. Plant life would have seemed very drab, just green and brown in colour. There were no flowering plants, so nothing like most of the common trees and shrubs today. What trees there were would have looked different, though some were relatives of modern day ferns and podocarps. There was no grass. Instead, low ground cover would have been ferns and mosses.

The Triassic world was unusual for another reason. About 20 million years before the appearance of the first dinosaurs, the biggest extinction the world had ever known had occurred. Over 90% of all plant and animal species then alive on land and in the sea had died out at this time. Even in the Late Triassic the world was still recovering, and there was not the usual variety of life normally found on earth.

It took more than 10 million years before ecosystems recovered and complex systems and larger animals took even longer. Most of the dominant land animals that were around when dinosaurs evolved were products of long and established lines of descent.

A giant desert

The continents of the triassic Earth were configured differently to today. All the land masses on the planet were joined together into one huge continent called Pangaea. This stretched from pole to pole and its central region was a vast inhospitable desert. We know this because the type of rocks that were deposited at this time have sedimentary features characteristic of a dry harsh climate.

As all the continents were connected, the animals and plants found in the fossil record from that time are very similar all over the world.

	Peteinosaurus caught insects in its pin-like teeth.

New life

The Late Triassic was an innovative time in the animal kingdom. By the end of the period not only the dinosaurs had appeared but also pterosaurs (flying reptiles), various kinds of marine reptiles, the first crocodiles and turtles, and the earliest true mammals.

Towards the end of the Triassic, 220 million years ago, there was another extinction, which wiped out many of the non-dinosaurs including the dicynodonts such as Placerias and primitive archosaurs such as Postosuchus. It was after this that dinosaurs really started to radiate and diversify.

Dinosaurs gain the edge

It was often assumed that the dinosaurs survived due to their superior speed and agility. We now think they were simply fortunate because they were not hit as hard by extinction. After the extinction at the very end of the Triassic, the dinosaurs were the only large land animals left.