Cretaceous Period

Wednesday, December 22, 2010



Introduction:

The Cretaceous Period was the last phase of the Mesozoic era and spanned for an interval of 75 million years from 135-65 million years ago. Although the dinosaurs died out in this period many interesting dinosaurs like the Tyrannosaurus Rex and the Triceratops appeared making this period quite interesting.

Other important things that happened during the cretaceous included further splitting of the pangea breaking it down even further into the smaller continents we recognise today.

The cretaceous also denoted a start in the appearance of flowering plants like magnolias and water lilies as well as many of the modern insects we know of today. Examples include ants, butterflies, grasshoppers, termites and aphids. All of the above meant that the cretaceous truly was a an amazing and diverse period for life on the planet earth, sadly it was also the end of the dinosaurs but with over 180 million years of domination I don’t think they can complain.

More Pangea Splitting :

Ever since Laurasia split from Gondwana in the jurassic further splits and rifts within these 2 lesser continents continued to happen during the cretaceous.Gondwana finally split into four smaller pieces namely Africa, South America, India and Antarctica/Australia whilst Laurasia was still moving further away into the northern hemisphere.

This splitting of the Earths major land masses would continue well on into the Cenozoic era even after the dinosaurs had become extinct until it would finally resemble what we see on modern day maps. Remember these rifts are still happening today and maybe in millions of years from now the landscape of the earth will change once again.

High Ocean Levels :

During the cretaceous period the sea levels rose all over the world resulting in the submerging of at least one third of the earth’s land area. Why there was so much water can be attributed to three possible reasons.

* There were no frozen poles during the cretaceous (or jurassic), this reason alone meant that water levels were generally higher during the Mesozoic era.
* In general because of the higher temperatures that existed during this time a thermal expansion of the ocean waters meant a greater volume for the same mass of water. If we look at the temperatures on the ocean bed today they are close to 3-4 degrees centigrade whereas during the cretaceous they would have been as high as 15 degrees centigrade which demonstrates a real difference in overal temperatures.
* Both the jurassic and the cretaceous contained huge levels of volcanic activity thanks to the constant tectonic changes happening within the earth. This meant that much of the oceans surface consisted of erupting volcanoes filling the sea bed with mini mountain ranges thus making the oceans extremely shallow and causing them to contain less water thus flooding much of the earths then low lying land.

General Climate :

As far as living species were concerned temperatures were much lower and more importantly stable for most of the cretaceous. Compared to the triassic and jurassic periods better temperatures meant created a much more hospitable environment for animals and plants to diversify.

This massive climate change was mainly due to the changes happening at the tectonic level, the cretaceous was in general a much wetter period with oceans flooding the land to create many lakes, rivers and swamps.

All this extra water offered great opportunities for diversification in both animals and plants, of course the tectonic movements much volcanic activity which as we shall see had a massive impact on temperatures towards the end of the cretaceous period where global warming and a possible asteroid hitting the earth caused the massive dinosaur extinction commonly referred to as the cretaceous tertiary extinction

Cretaceous Plant Life :

The biggest change in the cretaceous had to be the appearance and advancement of flowering plants. Until now the dominant plant life consisted of cycads, seed ferns and confiers. The introduction of flowering plants added a totally new dimension to the ecological landscape and by the end of the cretaceous they pretty much took over as the dominiating plant species.

The plant life during the cretaceous took a very modern appearance making the landscape very similar to todays tropical jungles and forests. The angiosperms success and spread during the cretaceous was significant in supporting the birth of many new insect and mammal species. This was truly an exceptional and hugely diverse time for both animals and plants, and one that would start the end of the dinosaurs and the start of new life in the cenozoic era.

Cretaceous Animals :

In the Cretaceous period dinosaurs reached the peak of their dominance. It was during this time that the horned dinosaurs like the Centrosaurus and Triceratops appeared. The duckbilled Parasaurolophus, the armored Ankylosaurus, and the well known Tyrannosaurus also made their first appearance during the cretaceous.

Both birds and the flying reptiles such as the pterosaurs were now much more developed and completely dominated the skies.

In the sea ichthyosaurs, plesiosaurs and sharks continued to dominate marine life as they did in much of the jurassic. However new predators namely Mosasaurs who were snake like reptiles also came into existance during this hugely diverse time period. These ferocious creatures lived in lagoon and shallow water areas where they would aggressively ambush passing prey. Other animals that appeared in the cretaceous include large crocodiles, turtles, snakes and lizards.

Dinosaur Extinction :


At the end of the cretaceous period a mass extinction second only to the permian triassic extinction wiped out over 80% of all living species on the planet earth. It wasn’t just the dinosaurs that were affected, pterosaurs, mosasaurs, plesiosaurs, ammonites, belemnites and many other species which were common at that time simply dissappeared.

Its not 100% clear what caused the extinction but some key factors which certainly contributed to it include the striking of a massive asteroid approximately 10 kilometres in diameter. This asteroid landed in the Yucatan peninsula in Mexico and would have had disasterous consequences ranging from forest fires to sunlight blocking dust and causing mass darkness and death to both animal and plant life.

Of course there are other theories related to huge volcanic eruptions, global warming and even disease amongst the dinosaurs. Again nothing is confirmed except that the death of the dinosaurs paved the way for a new wave of mammal species which took over and dominated in the Cenozoic era.

Source from :http://www.dinosaur-facts.com

For more information related to dinosaurs, visit rareresource.com.




1 comments:

Charles Weber said...

The Cretaceous ocean predators were very large. I suspect that the productivity implied by this was caused by a flow of phosphorus toward the ocean from the savannas (seasonal rainfall areas) permitted by erosion of phosphorus rich runways of plant smothering termites in the Amitermitinae starting in late Jurassic in Australia where the first ocean phosphorite deposits occurred. Anoxic conditions in the oceans were also probably caused by this. This anoxic bottom condition probably helped reduce the ammonites also, in addition to competition from phosphorus enhanced vertebrates. The savanna herbivore dinosaurs declined in armor, teeth, and quite a bit in bony structure across the Cretaceous outside of South America, especially in southeast Asia. Many even lost teeth. I suggest it was due to this same phosphorus famine created by erosion of the soil of the runways of plant smothering termites. Pterosaurs and birds probably lost teeth primarily because of the young eating iron oxide and bauxite in the flying reproductive soil borne termites’ guts, which bound the phosphates. You may see this discussed in more detail starting in http://www.angelfire.com/nc/isoptera/termites.html and its links, which links explore the possible affect that ant evolution had upon them. By the time the Cretaceous ended the world ended up with tiny savanna vertebrates, most of them mammals, which were able to give their young phosphorus in milk at that critical stage. They were a far cry from the massive, well boned Stegosaurs, etc., which roamed around the Jurassic, and had diminished tooth structure at first. They were a long time starting to increase in size (several million years).
You may see the affects on soil discussed in more detail in http://www.angelfire.com/nc/isoptera/soil.html .
Sincerely, Charles Weber

PS It is conceivable that you would also find interesting a hypothesis of my son explaining the Decca (or Deccan) lava flows as disruption of the crust by the disruption of the crust at the antipode (opposite side of a sphere) by a huge meteorite impact. You may see my version in http://charles_w.tripod.com/antipode.html .
Sincerely, Charles Weber

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