The Cretaceous Period: Major Events, Animals, and When It Lasted


The age of dinosaurs ended with the Cretaceous period. Even so, new dinosaurs still appeared at this time. The first pachycephalosaurs and ceratopsian dinosaurs appeared during this period. Fossils of the earliest modern flowering plants, insects, birds, and mammals date from this time.

What are the important things you need to know about the Cretaceous Period? Let’s study the following information and understand the major events, animals, as well as the duration of this significant period.

Major events

The Cretaceous period is known for the K-Pg extinction event. This event happened about 66 million years ago. During this time, many invertebrates and large vertebrates have disappeared. This biological, geological and climatic event had consequences. Here are the highlights of this period.

The K-Pg extinction event (Cretaceous-Paleogene)

Scientists called it the K-Pg extinction event because it happened between the Cretaceous and Paleogene periods. It was formerly called the Cretaceous-Tertiary or KT event. Experts have discovered evidence of a blast impact from an asteroid 10 kilometers or six miles in diameter. The asteroid impact caused massive tsunamis and shock waves. It also unleashed a large cloud of dust and hot rocks in Earth’s atmosphere. The extremely hot sediments fell back to Earth and started fires. These events further augmented the planet’s atmosphere.

The tremendous heat cooked the animals alive, especially those that were too big to find a place to hide. Small animals could hide in large tree trunks, underground, in caves or under water. They may have survived the first heatstroke. Particles of dust and debris remained in the atmosphere. These blocked the sunlight that animals and plants needed. The reduced amount of sunlight has caused the planet’s temperature to drop. This could have weakened large animals that needed large amounts of energy.

Small land animals that ate plants and other animals survived as scavengers of decaying plants, roots, dead dinosaurs, and fungi. They were birds, lizards, mammals or archelon turtles. These little animals had low metabolic rates, which allowed them to wait out the disaster. Scientists believe that massive volcanic eruptions in the Deccan Traps between Asia and India occurred before the K-Pg event. This may have contributed to the mass extinction.

Extinction event
The tremendous heat of the K-Pg (Cretaceous-Paleogene) extinction event cooked many animals alive.


The Cretaceous climate

The planet was warmer at that time. Many fossils of animals and tropical plants bear witness to this. Nuclear winter happened when the asteroid hit Earth. Particles suspended in the atmosphere caused a sharp drop in temperature.

The Cretaceous period allowed the first diversification and the appearance of flowering plants. Different organisms, such as insects, evolved as they took advantage of the new food sources that these new plants offered them. Cycads, seed ferns and ginkgos have been replaced by conifers. Marine life continued to flourish. It has become even more diverse.

Rudist molluscs have created whole new coral reefs. The tyrannosaurus rex became the largest terrestrial predator. Quetzalcoatlus was the largest flying organism. Reptiles ruled.


Dinosaurs were the most numerous animals during the Cretaceous period. Among them, some groups have become more dominant than others. Sauropods filled the southern parts of the planet. They were rare in the northern continents.

Antarctica was full of Ornithischians, like the Iguanodon, which stayed in herds. Towards the end of this period, large groups of Triceratops fed on low plants and cycads in the north. The T-rex dominated with them. The Spinosaurus were the great meat eaters of the south. Placental mammals also began to appear during the Cretaceous period.

Large pterosaurs dominated the air. The ancestors of modern sandpipers, pelicans, grebes and cormorants also appeared at this time. The shallow, warm oceans were filled with plesiosaurs. Sharks and rays have also started appearing, along with starfish and sea urchins. Coral reefs continued to grow. Diatoms also began to thrive.

Sauropods were an important animal of this period.

Daniel Eskridge/

marine life

This part of the planet at the time was divided between the Boreal and the Tethysian. The reef-like structures were ruled by rudist molluscs. They were strange, large bivalves. One valve was shaped like a flattened cap and the other was shaped like a cylindrical vase. These bivalves did not grow in the Tethys region. They stayed in the boreal region to create coral reefs. The rudist molluscs found elsewhere did not make coral reefs.

Organisms such as ammonites, echinoids, benthic foraminifera, nerineid snails, and calcareous algae dominated the Tethys region. The Belemnites remained in the boreal waters. Dinoflagellates, diatoms and radiolarians were less abundant but important at this time. Ammonites fed on free-swimming invertebrates.

Large animals, such as mosasaurs, fed on ammonites. Ichthyosaurs, plesiosaurs, rays and sharks appeared and ruled the oceans. Large ray-finned fish called teleost fish were the largest teleosts. They grew at least 15 feet or 4.5 meters.

terrestrial life

Dinosaurs continued to rule the lands from the Cretaceous period. During the latter part of the period, many dinosaurs lived differently from many modern mammal groups. Placental mammals evolved during the latter part of the Cretaceous. These animals include modern mammals. Almost all of them were smaller than today’s rabbits. Cretaceous placental mammals were believed to thrive in terrestrial territories when the dinosaurs died out.

Marsupials also began to evolve during this period. This group of animals includes opossums, kangaroos, and koalas. Modern birds descended from a reptilian ancestor from the Cretaceous and Jurassic periods. Hesperornis was a flightless bird during the Cretaceous period. It had a beak with sharp, backward-pointing teeth and large feet. These traits were all for catching fish.

Evolution came to dinosaurs and mammals. Dinosaurs that had mammalian traits retained their large populations for millions of years after the dinosaurs became extinct. Then, dinosaurs and mammals became great evolutionary opportunists. Dinosaurs evolved as much as they could and succeeded in all parts of the world.

They have continued to evolve to adapt to their increasingly diverse environment. Mammals did the same. This could be one of the reasons why mammals survived after the extinction of the dinosaurs. Like the dinosaurs before them, mammals occupied every environmental niche around the world.

When it lasted

The Cretaceous period began with the joining of two major continents of the supercontinent, Pangea. Gondwana to the south and Laurasia to the north. The Tethys Seaway, along with the various segments of Gondwana and Laurasia, began to separate the two continents. At the end of the Cretaceous, most continents were already in their current location. Australia was still attached to Antarctica and India was then alone in the Indian Ocean.

It was warmer at that time. It was even more humid than in the modern tropics. This was mainly because of the high level of volcanic activity at the time. The polar regions were all covered in lush forests, not ice caps. Dinosaurs thrived in Antarctica, even in winter.

The extinction event at the end of the Cretaceous erased the dinosaurs from the planet. The birds were the ones that remained in the air and on the ground. Marine reptiles have also disappeared. But when these animals said goodbye, many organisms arose. The rise of flowering plants gave surviving animals another good source of food. gastropods, snakescrocodilians, lizards, mammals and amphibians went through the extinction event that killed the dinosaurs.

The Cretaceous period took place 145.5 to 65.5 million years ago. It was then that other ribs appeared. The seasons also became more evident as the planet’s climate cooled. Magnolias, oaks and walnut trees began to thrive in the north during the late Cretaceous.

At the end of this period, a huge asteroid hit the planet. This led to the extinction of many of the existing species on the planet at the time. Yet many scientists believe that many species became extinct even before the extinction level event. They said it was because of climate change. Other possible causes are heat waves, freezing cold spells, infertility and disease. Egg-eating mammals and radiation from an exploding supernova.

There could also be a lack of genetic diversity among dinosaurs. This could have been caused by the isolation of each group in specific areas of the planet. Inbreeding would probably have caused diseases to reappear with each generation. Illnesses could have caused their bodies to develop deformities or weaken their immunity. These problems could have resulted in a huge intolerance to changes caused by land changes, climate and changes in diet.

About 80% of all animal species were wiped out at the time. Many of these animals were important during the Mesozoic era. Most dinosaurs and many marine invertebrates have been wiped out. Even so, many animals and plants are still fueled by this event to extinction levels.

Earth 200 million years ago: Pangea

Rashevskyi Viacheslav/


The Cretaceous period is one of the most crucial periods in the evolution of the Earth. The division of the supercontinent, Pangea, into Laurasia and Gondwana resulted in greater diversity among animals and plants. Flowering plants have provided another sustainable food source for many animals. Even though the dinosaurs disappeared during the last Cretaceous period, new species emerged and flourished.


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