They died off suddenly?
Suppose, they were introduced for purposes which they fulfilled. When they were no longer needed, they were destroyed, discontinued or just permitted to die out. Then, other creatures were introduced to replace them.
Let's suppose for a moment that you had in mind to create a world that would be able to sustain an environment for your favorite creature. A bipedal, intelligent more or less hairless being that would be very inventive and resourceful. That one day would fabricate all sorts of vehicles for getting around quickly on the planet home.
Let's see, oil would make a nice fuel for powering these machines and heating the homes needed and sustaining industry to allow these beings to display their capacity to put all that oil to work.
To make great oil reserves deep underground waiting to be tapped and put to all sorts of uses would require vast quantities of organic materials, plants, trees, grass, seaweed, etc. With all that plant material, you need lots of plant eating creatures to help process that material. Why not all sorts of giant animals with big bellies and huge appetites?
What about when there became too many of these beasts to manage the available food material. If they ate all the plants, none would be left to seed future plants. So you keep their numbers in check by including predators as well. All this eating and dying would create a huge mass of organic material piling deeper and deeper till you decide you've got enough raw material to process the oil you need.
So, you create a worldwide cataclysm big enough to trap all that organic material beneath hundreds of feed of soil and rock. Deep enough that the weight of everything above can process the material into a raw oily deposits ready to be tapped and utilized at the right point in time many years later.
In a senario such as this, you can see that the great creatures such as earth's dinosaurs could have a special purpose for their time. Once they had finished the task they were wiped out. After all, you wouldn't want them threatening or causing problems for your special beings.
Wayne Hollyoak
