The wind blew too hard for them.
It became too warm for them.
No one knows for sure.
There were huge earthquakes
There was a McDonalds on the corner
There were people on earth
A volcano erupted blocking out the sun.
There was a space invasion.
A meteorite hit earth and added soot to the air.
A giant dinosaur ate them and is now hiding.
Some kinds of plants died, too
No other living things were around
The climate didn't change at all
Not enough air
Not enough water
Not enough food
A rain storm
An extinct animal
A tool that scientists use
A place where dinosaurs lived
Something new that has been found