The Cretaceous Period is the last period of the Mesozoic Era, beginning approximately 145 million years ago and ending with the great extinction of the Cretaceous, which ended with the hegemony of the dinosaurs 65 million years ago.
The entrance to the Cretaceous was due to an extinction of species not as great as the one at the end of the Mesozoic, but some striking taxa such as the Stegosaurus and some species of Sauropods became extinct, with a decrease in the number of representative families in this era.
Lower Cretaceous. We can subdivide it into two: Neocomian and Aptian-Albian. It begins 145 million years ago and ends 125 million years ago.
- Neocomian is characterized by the destructuring of Laurasia and Gondwana, subdivided into subcontinents that will give a geography more similar to the current one.
- Aptian-Albian is characterized by the greatest evolution and radiation of dinosaurs that took place in present-day China.
Upper Cretaceous. We can also subdivide it into two parts: Upper Cretaceous and Lower Cretaceous. It begins 125 million years ago and ends 65 million years ago.
- High Cretaceous. Angiosperms are the leading plants, they have displaced gymnosperms in almost all niches.
- Lower Cretaceous. The end of the Cretaceous and the dinosaur era.
The Cretaceous already had a more similar separation of the continents to the present one, although with small changes such as only observing the mountain ranges that exist today (the Rocky Mountains in North America, Andes in South America, part of the Himalayas in Asia), the Indian subcontinent was still close to Africa but was already in the direction of Asia, Europe was comprised of an archipelago of large islands, and Australia and New Zealand were still linked to Antarctica.
The climate at the beginning of the Cretaceous was warm but with cool winters, it has even been said that there could be snowy areas at sea level (remember that before the only snowy areas were the mountain peaks).
At the end of the Cretaceous Period, no data have been found to indicate ice in any area, but cool winters have been found. The climate was therefore similar to the current one so that in Ecuador it was very warm and as we approach the poles it is getting colder, but it was even warmer than it is today.
We have already said in the Jurassic that the Inferior Cretaceous dates back to the oldest angiosperm with exactitude. During the Cretaceous period, the apogee of the angiosperms, the flowering plants, begins, which gives a great variety of colors.
Although they appeared 125 million years ago (exactly because pollen remains of Jurassic angiosperms have been found), it is not until 100 million years ago that the first angiosperm tree was dated.
That is to say, the first angiosperms were small plants that were not very striking in size, but still attracted more insects (or wind-blown) and allowed them to disperse quickly, taking away the ground from the gymnosperms.
The appearance of angiosperms caused gymnosperms to move, to migrate to areas where angiosperms were not comfortable.
They migrated to colder areas (mountain peaks and to the poles) and to areas of extreme conditions (extreme salinity, water stress, etc.).
Later on, Europe would be greatly favoured in one aspect of the migration of gymnosperms, namely that the Mediterranean Sea would create a natural barrier to the passage of plant species, forcing them to survive (coexistence with angiosperms or evolution to better withstand extreme environments) or become extinct (not all of them were able to survive).
This favors the Italic, Balkan and Iberian Peninsulas, as they have unique and exclusive plant species from each area that do not appear in others.
The passage to the Cretaceous caused the loss of the largest land animals (sauropods), although niches were left free for the appearance of other smaller ones such as the hadrosaurs and ceratopsians.
These large animals, although not as large as the sauropods, managed to evolve very quickly thanks to the disappearance of the colossal sauropods, and thanks to the fact that, as we have said in the Triassic, after extinction the radiation of the existing animals is favored.
Meanwhile, in the group of theropods, evolution came as a surprise: not only did large species like the Carcharodontosaurus or the Gigantosaurus develop, but smaller dinosaurs like the Iberomesornis and others considered true prehistoric birds (not like the Archaeopteryx, which is still considered an ancestor).
Although we have already spoken of the great extinction of the Cretaceous, and also of other theories, the great extinction is a topic to talk about.
This extinction meant the loss of almost 90% of life on Earth, both of aerial (pteranodons), marine (plesiosaurs) and terrestrial (non-avian dinosaurs) species, with the Third Great Extinction being surpassed by the Ordovician and Permian.
The most accepted theory is that of the meteorite, but before it fell on Earth things had already been happening.
The disproportionate increase in the number of dinosaurs and their lack of control was taking its toll: they could not be sustained.
Species normally seek a climax state, in ecology, it is the state to which they aspire to remain constant and in balance with Nature in order to sustain and maintain the ecosystem alive.
It is not known why, but the dinosaurs began to descend before their total disappearance, it is not known if by a worldwide epidemic, an excess of individuals (overpopulation), or simply that their time came to them (all species are destined for extinction).
With the arrival of the meteor, he just put the icing on the cake. He pushed for an end to extinction.
But as we have indicated, after an extinction many niches remain free, and this favors that the surviving species survive, grow, evolve and repopulate the Earth. The Age of the Dinosaurs, the Mesozoic, ended, and the Cenozoic and the apogee of mammals began.
Here we show you the dinosaurs that lived in the Jurassic period: