Extinction- What is it ?
Species of animals and plants die out naturally for a number of reasons; such as,
disease, climate change and habitat loss. An increase in the diversity of groups,
called speciation, results from a modification and adaptation of a existing
species/group to create new members; for example, long necks of the group
sauropodomorpha (e.g., Dipladocidae) developed to take advantage of food sources
higher up trees.
The rate of diversification is a good indication of ecological and biological
stresses put upon a group. The inability of a group to cope with stressful
circumstances by; speciation, adaptation or endurance, will result in extinction.
Figure 3: Shows the location dinosaurs fossils
leading up to the K-T boundaty
It is widely accepted that all geological time periods have a continous level
of extinction, known as background extinction. This means that a certain number
of species are expected to die out, the average species life expectancy is
approximately 4 million years or 20 Ma at the generic level (Sepkoski).
Dodson estimated that dinosaur genera lived for 4-8 ma. Overall, dinosaurs were
alive on this Earth for approximately 150 million years, which proves they were
not a fragile or venerable by any means.
To determine the cause a mass extinction event (MEE), it is essential to
understand; the (how long were high levels of extinction's in
progress ?), the (how many species suffered and to what extent?)
and the (what species/niches were affected?) of the event in
question, Jablonski (1986a).
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