Cretaceous
The Cretaceous period is a geological period. This geological period lasted from about 145 to 66 million years ago. This period is counted as the third and final period of the Mesozoic Era. Also, this is the longest of all the geological periods among the entire Phanerozoic, this surpasses the Ediacaran and Cryogenian period as well in terms of size.
The name of this period is being derived from the Latin word ‘Creta’ meaning ‘Chalk’. As in this period, chalk was abundantly found in the latter half of this time.
In this section, we will discuss in detail the Cretaceous Period.
Cretaceous Period
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The Cretaceous period experienced a relatively warmer climate which resulted in the high eustatic sea levels which created a number of shallow inland seas. The oceans and seas in that time were populated with marine reptiles which are now extinct, ammonites and also rudists. While on the inland surface the dinosaurs dominated.
The world at that time was an ice-free place with the forests being extended towards the poles. In this time, groups of new mammals and birds originated. Flowering plants also appeared in this time which began to rapidly diversify in the region. These flowering plants became the dominant group of plants on the planet. This occurred by the end of the Cretaceous period, with the decline and extinction of the previously dominating gymnosperm groups.
The Cretaceous period ended with the Cretaceous-Paleogene. At this time a large mass of extinction took place. Many groups, including the non-avian dinosaurs, pterosaurs, and also large marine reptiles died out during this time.
Cretaceous Dinosaurs
In this time, Cretaceous Period, there lived types of dinosaurs who dominated the land surface. We will know about these Cretaceous Period Dinosaurs in this section:
First, the Afromimus means "Africa mimic". They are the genus of theropod dinosaurs. This originated from the early Cretaceous Elrhaz Formation of Niger. They are single-species organisms of the Niger. A. tenerensis is a name of such a species as named by Paul Sereno, whose parts of the right leg, vertebrae, and ribs found in the Tenere Desert. They were originally classified as an ornithomimosauria but later it was debated to be an abelisauroid.
Next, we have Aegyptosaurus which means 'Egypt’s lizard'. This name was given for the country in which this species was discovered. This lizard is a genus of the sauropod dinosaur who is believed to live in Africa 95 million years ago. This was during the Late Cretaceous Period. Like the sauropods, this species had a long neck with a small skull. This animal's long tail acted as a counterweight to its body mass.
Pictures of the types of Dinosaurs are attached below:
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Abelisaurus
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Achelousaurus
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Achillobator
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Aegyptosaurus
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Alamosaurus
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Albertaceratops
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Albertosaurus
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Alectrosaurus
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Alioramus
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Alvarezsaurus
Late Cretaceous
The Late Cretaceous is the younger most between the two epochs into which the Cretaceous geological period is being divided. The late Cretaceous period is divided into geologic time scales. The rock strata which are from the epoch form the Upper Cretaceous series. As mentioned, the name ‘Cretaceous’ is named after the white limestone, chalk. Chalk was extensively found in northern parts of France and is seen in the white cliffs of southwestern England.
About the climate of Late Cretaceous Period - The climate was quite warmer than the present climate, although during the beginning and the end of this period a cooling trend existed but in the end it adapted into a warmer type. The tropics only exited near the equatorial regions and the northern latitudes too experienced more seasonal type climatic conditions.
Cretaceous Extinction
The Cretaceous Paleogene abbreviated as the K-Pg extinction event was a sudden and massive extinction. Almost three-quarters of plants, animal species in this time, that is approximately 66 million years ago, became extinct. While, ectothermic species like the sea turtles, crocodilians and tetrapods weighing less than 25 kg survived. This marked the end of the Cretaceous period and the Mesozoic Period.
Cretaceous Period Animals
The dinosaurs were the dominant group of land animals, especially the “duck-billed” dinosaurs like the Shantungosaurus, and horned forms, like the Triceratops. Other giant marine reptiles like ichthyosaurs, mosasaurs, and the plesiosaurs were also common in the seas, also flying reptiles (like the pterosaurs) dominated the sky.
Herds of herbivorous ornithischians also lived during the Cretaceous, they were known as Iguanodon (they are a genus that includes duck-billed dinosaurs, known as the hadrosaurs), Ankylosaurus and the ceratopsians. Theropods, including Tyrannosaurus rex, also continued as apex predators till the end of the Cretaceous period.
Triassic Jurassic and Cretaceous
The Mesozoic period was preceded by the Palaeozoic Period which is then succeeded by the Cenozoic which meant new life. This era is being subdivided into three periods:
The Triassic
The Jurassic
The Cretaceous
They are further subdivided into epochs and ages.
Cretaceous Organisms
Ammonites, belemnites, and other molluscs, and the fish were being hunted by great "marine reptiles," and pterosaurs while the birds flapped and soared in the sky above.
Yet the Cretaceous period saw the emergence of many lifeforms which continued to play key roles in the coming Cenozoic world.
FAQs on Cretaceous Period
1. What does the name 'Cretaceous' mean and why was the period named that?
The name 'Cretaceous' originates from the Latin word 'creta,' which translates to chalk. This geological period is named for the extensive chalk deposits that are characteristic of its rock layers, most famously seen in the White Cliffs of Dover, England. These chalk beds are formed from the fossilised remains of tiny, single-celled marine algae called coccolithophores.
2. When did the Cretaceous Period occur on the geological time scale?
The Cretaceous Period was the final segment of the Mesozoic Era. It spanned from approximately 145 million years ago to 66 million years ago, beginning after the Jurassic Period and ending with the Cretaceous-Paleogene (K-Pg) extinction event.
3. What was the global climate like during the Cretaceous Period?
The Cretaceous Period was characterised by a warm, mild, and stable 'greenhouse' climate. Global temperatures were significantly higher than they are today, which meant there were no permanent polar ice caps. This warmth led to very high sea levels that flooded continental interiors, creating vast, shallow seas.
4. What were the most famous animals that lived during the Cretaceous Period?
The Cretaceous Period was the peak of the age of dinosaurs and other giant reptiles. The most notable animals included:
- Dinosaurs: Iconic species such as Tyrannosaurus rex, Triceratops, Velociraptor, and the massive sauropod Argentinosaurus dominated the land.
- Marine Reptiles: The oceans were ruled by formidable predators like the Mosasaurus and long-necked Elasmosaurus.
- Pterosaurs: Flying reptiles, including the giant Quetzalcoatlus, were the masters of the skies.
- Early Mammals and Birds: While dinosaurs reigned, small, shrew-like mammals and the first modern bird lineages were also evolving.
5. Did humans and dinosaurs live at the same time?
No, humans and non-avian dinosaurs did not live at the same time. The last dinosaurs went extinct at the end of the Cretaceous Period, approximately 66 million years ago. The earliest human ancestors, or hominins, appeared much later, only about 6 to 7 million years ago, leaving a gap of nearly 60 million years between them.
6. What were the major geological events of the Cretaceous Period?
The Cretaceous was a time of significant geological activity. The key events were the continued breakup of the supercontinent Pangaea into the continents we recognise today. The South Atlantic Ocean opened up as South America and Africa drifted apart, and India began its long northward journey towards Asia. This process of continental drift led to high levels of volcanic activity and the formation of new mountain ranges.
7. What was the K-Pg extinction event that ended the Cretaceous Period?
The Cretaceous-Paleogene (K-Pg) extinction event was a catastrophic mass extinction that occurred about 66 million years ago. It wiped out approximately 75% of all species on Earth, including all dinosaurs except for their avian relatives (birds). The primary cause is widely accepted to be the impact of a large asteroid in what is now the Yucatán Peninsula in Mexico, which triggered devastating global environmental changes.
8. How did the rise of flowering plants (angiosperms) change the world during the Cretaceous?
The evolution and diversification of flowering plants, or angiosperms, was a revolutionary biological event. They rapidly became the dominant form of plant life, which profoundly impacted ecosystems by creating new food sources for herbivores, leading to the co-evolution of pollinating insects like bees, and fundamentally reshaping landscapes across the globe.
9. Why is the Cretaceous Period so important for the modern economy?
The Cretaceous Period is incredibly important to our modern economy because the specific geological and biological conditions of the time were perfect for the formation of fossil fuels. The vast, shallow inland seas had high levels of marine life. When these organisms died, they were buried in sediment under low-oxygen conditions, eventually forming over 50% of the world's known oil and natural gas reserves.
10. How did the high sea levels of the Cretaceous Period affect the evolution of life?
The exceptionally high sea levels created large, shallow epicontinental seas that submerged vast areas of continents. This had two major evolutionary impacts: it created enormous new habitats for marine life to flourish, leading to great biodiversity in the oceans. Secondly, it acted as a barrier, isolating land-animal populations on different continental 'islands', which drove the evolution of unique and distinct species in different parts of the world.
