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The Dinosaur extinction was the K-C boundary, the cretacious-tertiary boundary between the mesozoic (age of reptiles) and the cenazoic (age of mamals). This was 65 mya. The P-T boundary was the mass extinction of 250 mya. This was the permian triasic boundary between the paleozoic (age of fish) and the mesozoic. Unless there was a new find, the last I was taught, this mass extinction was not caused by a comet, but was caused by the coalecence of the continents back into a one supercontinent stage (pangea) The enormouse environmental change wiped out 95% of the pre-existing biomass alowing for the next age to begin. The reptiles became dominant then because they occupied the niches that were freed by the death of anphibians who previously occupied those niches.

Note: A niche is a type of action or area in an ecosystem. i.e. eating fruit from a certain class of shrub is a niche.

When the next mass extinction took out the dinos' those niches became open for mamals to occupy. This leads back to the discussion on speciation where the mamals all evolve into the current ones via reproductive and/or social isolation brought about by geologic time. (MillionsYears).

Birds of a feather: The mamals in the canopy stop associating with the mamals on the forest floor. Neither of them associate with the mamals in the open plains, thus adaptation and selective pressure influence the developement of long necked mamals or trunked mamals, or mamals with strong tails etc.

Guiding with the light,
The Shepherd
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