Artwork showing the relative scale of humans and Giganotosaurus. Meaning 'giant southern reptile' this 12-m-long (39-ft) carnivore was the apex predator in what is now Argentina during the Late Cretaceous period, around 99 millions years ago. It was comparable in size - possibly slightly larger - than Tyrannosaurus rex. But they never crossed paths, as they lived 30 million years apart in different regions of the Americas.