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