Landscape during the Cretaceous period

Cretaceous period

The Cretaceous ended with the most famous mass extinction in history - the one that killed the dinosaurs. Prior to that, it was a warm period with no ice caps at the poles. Much of what we now know as dry land - such as southern England and the midwest of the USA - was underwater, since sea levels reached their highest ever during this time. The Atlantic Ocean grew much wider as North and South America drew apart from Europe and Africa. The Indian Ocean was formed at this time, and the island that was India began its journey north towards Asia.

Began: 142 million years ago

Ended: Cretaceous-Tertiary mass extinction
65 million years ago

What the Earth was like

A map of the Earth in the Cretaceous Period

Reconstruction of the Earth in the Cretaceous period, 142 million - 65 million years ago. Credit: Dr Ron Blakey, NAU Geology.

Causes of extinctions

During this period the following events are thought to have contributed to the Cretaceous-Tertiary mass extinction.

Flood basalt eruptions Flood basalt eruptions
Flood basalt eruptions are a type of large-scale volcanic activity, both in terms of extent and duration, that can occur on land or on the ocean floor. A flood basalt may continue to erupt for tens of thousands - possibly millions - of years and the lava can cover hundreds of thousands of kilometres.
Impact events Impact events
Impact events, proposed as causes of mass extinction, are when the planet is struck by a comet or meteor large enough to create a huge shockwave felt around the globe. Widespread dust and debris rain down, disrupting the climate and causing extinction on a global, rather than local, scale.

Types of fossils formed in this period

Life on Early Cretaceous Earth

By Dr Jo Wright

The Early Cretaceous Earth was home to the largest animals ever to fly. On the ground, life was changing too - and a species of dinosaur was about to undergo a very important change. Dr Jo Wright explains why.

Giant gliders

The largest animals ever to fly were pterosaurs. With wingspans of up to 12m, they could be as large as a small modern glider. Pterosaurs were a peculiar mixture of bird and bat. Their long beaks remind us of birds, but they had membranous wings like bats.

These wings were attached to their legs and they walked on all fours, with an erect, rather than sprawling posture. Although not necessarily very speedy on land, they walked competently. Their tracks have been found in rocks around the world.

There were two kinds of pterosaurs, ones with and others without tails. The tailed pterosaurs lived from the Late Triassic period to the Late Jurassic period, when they were replaced by the tailless ones. It is this second group, including Ornithocheirus, which grew to great sizes.

Early Cretaceous Earth

The early Cretaceous period was also a time of great change for animal life on the land. New types of dinosaurs - the ornithopods - were appearing, and they would later be among the most numerous on land.

Small versions of these dinosaurs had actually been around since the Early Jurassic period, but only now did they come into their own. Iguanodon was one of the earliest of the ornithopods. There were several species in Europe, Asia and North America.

Cheeky chewers

Although smaller than the sauropods, the ornithopods were more numerous. They were able to chew their food and hold it in their cheeks while doing so. Chewing broke their food into smaller pieces, greatly reducing digestion time. Sauropods didn't chew their food at all. They needed huge bodies so their guts could break down food over several days. As they didn't have cheeks, they had the big reptilian smile we see in modern lizards and crocodiles.

Bird-like dinosaurs

New kinds of theropods also appeared in the Early Cretaceous period. These were the kinds popularly known as 'raptors', such as Utahraptor and Velociraptor. These theropods were some of the most bird-like dinosaurs that ever existed. They had fairly long arms and a more bird-like pelvis. Birds are descended from theropod dinosaurs like these - over 100 characters in the skeleton link these groups. Fossil evidence from the USA indicates that these types of dinosaurs may have hunted in packs.

The power of flight

The earliest known bird - Archaeopteryx - comes from the Late Jurassic period in Germany. By the Early Cretaceous period, birds had radiated and diversified. Fossils have been found in Spain and China. Most of these early birds look very primitive and some still have teeth. But by the Late Cretaceous period they looked look far more modern and had diversified into different niches. Some wading or diving birds had even lost their power of flight again.

A world of colour

In the plant kingdom there were great changes too. Flowering plants appeared in the Late Jurassic period, and in the Early Cretaceous period the first flowers appeared. Soon flowers and flowering plants were to become the most common plants on Earth.

The earliest known fossil flower is very small. It was found in the Wealden Formation sediments of southern England. During the Early Cretaceous period, southern England was a low-lying, richly vegetated river floodplain. The climate was humid and sub-tropical, although there may have been wet and dry seasons, as there is evidence of forest fires. By the Late Cretaceous period the world would have looked rather more familiar to us, although there were still no grasses.

BBC News about Cretaceous period