X is for ‘X’tinct

As we are nearing the end of the alphabet and the idea is about extinction, I think we might just get away with this.  A playful take on what has happened to most of the giant mammals that once graced this planet.  Two legs or four?

It is estimated that dinosaurs became extinct around 61 million years ago. The most popular theory as to why suggests a large asteroid or comet collided with Earth about 65 million years ago. Scientists think that such a large collision would throw so much dust into the air that sunlight would not be able to shine and plants and animals would die.