The answers are:
A. dinosaurs
- Dinosaurs were the dominant life form during the Mesozoic Era, they came in in all shapes and sizes, from little chicken-sized raptors to giant herbivorous creatures. In general, they were split into two groups, which roughly corresponds with the way of movement, bipedal or fourlegged.
B. birds
- The Archaeopteryx was the so-called missing link in the bird's evolution, once this creature was discovered the things became much clearer. It is a perfect creature that is like a crossbreed of a little raptor and a bird.
B. a meteorite collision
- Around 65 million years ago a big meteorite hit the Earth, right of the eastern coast of Mexico, near Yucatan, and it managed to release an enormous amount of force and also trigger much of the volcanoes that caused a global climate change in just a few days that exterminated the dinosaurs.