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What event occurred at the division between the Triassic and Jurassic periods, and why was this important to the dinosaurs? The extinction is a topic that now requires rather more digging than talking. The Triassic and Jurassic periods were remarked by changes that influenced both: relief and biologic forms of life. The dinosaurs were the most typical representatives of fauna for the Triassic and Jurassic periods. These periods are characterized by tectonic activity, worsening of climate conditions and changes in fauna. The extinction of dinosaurs, that had been dominating land animals within the previous period, took place.
The Triassic Period The Triassic Period is considered as the beginning of the Age of Reptiles. The continents consisted of one extraordinary continent Pangea. During the Triassic Period Pangea started to slit into parts (Gondvana and Lavr asia). The Atlantic Ocean appeared. The sea level was not very high. The mild climate became dry and contributed into formation of deserts in continental areas.
Small lakes and seas started to evaporate intensively and the water became salty. Dinosaurs became the dominating species among land animals of this period. The first frogs, crocodiles and turtles appeared together with the first mammals. Almost all species of ammonites died out till the end of the Triassic period. The Jurassic Period Giant continent Pangea was in the process of active division into parts till the end of Jurassic period.
Vast continent called Gondvana still existed and spread to the South from equator. Later it broke into parts and created continents that are known now as Australia, India, Africa and South America. The sea inundated considerable part of continents. The climate changed and became mild and damp. Land animals from the Northern hemisphere werent able to migrate from one continent to the other; however they were still able to inhabit the whole mega-continent. Dinosaurs extinction: the main theories It is very difficult to support one hypothesis related to the extinction of dinosaurs, taking into account the variety of geographical and historical events in relation of time, life cycles, eco geographical areas, etc.
We need to examine a number of factors such as changes of climate, changes of flora, competition, preying on others, diseases, etc. These factors, probably, had influence on different species of dinosaurs in different ways. Some combinations of factors could have an unfavorable, probably even fatal influence upon some species. If there were one reason, it could be some definite reason, such as general orographical and climate change that took place during this period and resulted in grave consequences in different ecosystems. Any substantial change in climate or any other physical change inevitably disturbs the equilibrium of species. Such change is favorable to some species and unfavorable to the others; in such a way the extinction takes place.
Lets examine several hypotheses of dinosaurs extinction. According to one of hypotheses proposed by scientists, the dinosaurs disappeared not because they lost their food supply but because of asteroid impact. Several anthropologists support the asteroid theory, claiming that dinosaurs are the biggest and slowest animals in the environment. These kinds of animals are very vulnerable to changes in environment, but not to climate change. The scientists consider as evidence a crater in Manicouagan in British Columbia, Canada, to support their theory.
The anthropologists also advanced another hypothesis. They supposed that the cause of dinosaurs extinction were new conditions of climate due to very large lava flows, in particular. They focus attention that rapidly changing climate between the Triassic and Jurassic periods did in the fauna, as they are called, by transforming their habitat. The Triassic and Jurassic periods were characterized by quite steady climate and dinosaurs adapted themselves to it. Due to the impact of very large lava flows, separate dinosaurs died either because of physiological influence of climate and other side effects such as the emission of carbon dioxide and sulfur aerosols, or because of hunger. Such deaths could finally bring to extinction of dinosaurs in general.
New climate had unfavorable indirect influence on many dinosaurs, changing the flora in places of their inhabitants. There is certain interdependence between general size of mammals and their extinction. Such interdependence is coordinated with the climate hypothesis. We know that the mortality among small dinosaurs wasnt as high as the mortality among big dinosaurs during that epoque. Besides, the major part of small dinosaurs had more changes to survive. Moreover, the reproductive cycles of smaller dinosaurs are quite short so small dinosaurs can adapt themselves to the climate with seasonal fluctuation in temperature.
There is another hypothesis that is based on weak immune system of dinosaurs. Scientists who find neither the climatic nor the asteroid theory convincing argue that rampant disease was the main villain. In this view, the dinosaurs were betrayed not by the naivete of the big animals themselves but that of their immune systems. It is very important to define the reason and the date of dinosaurs extinction not only from biological but also from geological point of view. Usually the scientists consider the changes in climate to be the only reason of dinosaurs extinction. Another reason is the impact of asteroid for fauna (dinosaurs in particular).
There is no doubt that these factors were very important but probably they werent the determinatives. Modern scientists also recall the geological hypothesis that is closely related to so-called theory of catastrophes. By their opinion, catastrophes, probably, could take place at the early stages of forming of flora and fauna. Really, it is not correct to examine the reasons of one of the latest global catastrophes at the edge of the Triassic and Jurassic periods not taking into account the extinct fauna. Modern scientists propose numerous global, regional, local (for all species of dinosaurs of one area) and particular (for definite species of dinosaurs) hypotheses. Sometimes these hypotheses supplement each other; sometimes they are mutually exclusive.
The workout of synthetic concept that will organically include all correct suppositions of previous hypotheses should become the inevitable stage of problem. In conclusion I want to summarize all main theories related to the dinosaurs extinction. So, there are approximately five main hypotheses, explaining the reasons of extinction. They can be singled out as follows: the extinction of species due to asteroid impact (a crater in Manicouagan in British Columbia, Canada); new conditions of climate due to very large lava flows, in particular (physiological influence of climate and other side effects such as the emission of carbon dioxide and sulfur aerosols, etc) some changes in climate that influenced changes in flora (food for the large mammals); the extinction of species due to natural reasons; the mysterious virus (scientists argue that a rampant disease was the main villain); Yet, the changes in climate took place before and dinosaurs didnt extinct only due to this reason. It is also difficult to solve this problem on the base of concept of the species ageing. Probably, we can get to truth when we combine all the reasons together.
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