Pterosaurs, such as the Quetzalcoatlus, were as tall as a giraffe and bigger than the biggest flying birds. Many pterosaur researchers are convinced that they could fly. This is due to the different ways birds and pterosaurs evolved powered flight. Birds take off using their legs to get airborne and then their wings to actually fly, which means they have to carry around big, heavy leg muscles as they fly - essentially dead weight. However, paleontologists think that pterosaurs took off more like vampire bats, using all four of their limbs to do a burpee-like movement. This allowed them to use the same muscles to take off and fly, making the animal lighter overall. So, sorry birds, pterosaurs have you beaten in the body plan department, making them the biggest flyers of all time.