In Mexico, the first region to be hit by the asteroid, life still remains. Buried in the cool ground inside its egg, an "Alamosaurus" baby has survived. And so has an adult "Alamosaurus". All around the world, small handfuls of dinosaurs try to start over. But their species are already considered extinct. In order to survive, any species needs to maintain a critical mass of population. If it falls below that threshold, then there's no way to climb back from certain extinction.