Introduction


Extinction of the dinosaurs has come to symbolize the Cretaceous/Tertiary mass extinction event. The impact theory, proposed by Alvarez others (1980), renewed ethusiasm among scientists to find an a acceptable explanation which satisifies all of the observed, and commonly contridicting evidence, associated with the Cretaceous-Tertiary (K-T) boundary. This debate has been in progress for 18 yrs now, therefore, it can be seen that there is no clearcut answer.

To find out a brief history of the dinosaur; Click on the scroll





Limitations of evidence


Literature surrounding this topic produces many contradictions, with respect to; absolute numbers of genera, their relative location in time, correlation of different stratagraphic units and, thus, the overall nature of their extinction. This problem is a result of the fact that the fossil record is very incomplete.

It is important to view all the evidence presented here knowing that very little is an absolute fact and that new theories develope from increased knowledge. Continued field work and analysis will eventually reveal the answers to one of the greatest debates science has encountered.




What is extinction and how is it measured ?;
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Nature Of the K-T Extinction


Selective extinction did occur at the K-T boundary (Officer et al, 1987) as many groups passed into the Tertiary unscathed. Most biotic changes are related to short-term loss of primary productivity (Coorough and Fastovsky, 1996). Animals in food chains who obtained there food supply derived from photosynthesis suffered the greatest in the K-T extinction.


What is the evidence ? Follow Steggy back in time, to find out






Survivors



Many clades reestablished themsevles after the K-T extinction with little change in habitat, while others changed their lifestyles dramatically.
The species of flora (plants) and fauna (animals) which suffered the highested losses cannot be grouped together by one single characteristic. Detritus-feeders (i.e.scavengers of terrestrial and marine habitats), and animals that could withstand prolonged periods of starvation e.g. 7 months, preferentially survived whereas animals requiring green plants for food tended to become extinct. However, many detrius-feeders did become extinct and many herbivores survived!




What was the climate like? Fasten seat belts for a rocky ride



Why; The Causes of Dinosaur Extinction

Their demise was probably due to starvation through global collapse in the producitivity of green plants (Sheenan and Fastovsky, 1992) caused by darkness and acid rain (Hildebrand, 1993). Perhaps a question of vunerability, dinosaurs were large creatures with small populations, and it was their lack of ability to evolve and occupy new niches, (Officer et al, 1987).

Perhaps it looked like this ?





Conclusions



  • Need to be able to link the sweep of biotic changes during the Masstrichtian as a whole.

  • The era of the dinosaurs did not end because they were in decline but rather they were changing into creature that were more diverse, more active and more cerebral (brainy),therby more similar to modern birds and mammals. (Russell, 1996)

  • Hulbert & Archibald concluded in 1995, that there is not enough evidence to argue for a sudden or gradual decline in dinosaur taxa at the end of the Cretaceous. It must be iterated again, due to the lack of terrestrial K-T sequences, that there are no means to test this evidence to see if is a local or global phenomenon. A nest site in China, also of the magnetochron 29r, indicates the presence of dinosaurs but cannot provide any evidence with respect to; diversity and rate of decline. Absence of mass mortality deposits at the K-T boundary constitues a weakness in the asteroid impact theory for the extinction of the dinosaurs, Cutler and Behrensmeyer (1996).

  • Dinosaurs declined in diversity over the last several million years of the Cretaceous, of which seems to accelerate towards the boundary, as depicted in North America. However, there is no other evidence for the timing and nature of this extinction in the rest of the world.

  • A major upset in the reproductive cycle of dinosaurs would result in a rapid and dramatic decrease in population.




    References


    Glossary: will arrive soon!


  • Dinosaurs that are still alive:- Just a bit of fun


    Thesaurus: Dictionary type book
    Mumsaurus: Reason for being grounded after being caught doing something naughty!