T-Rex Never Met a Stegosaurus — They Missed Each Other by 80 Million Years

Picture a battle between Tyrannosaurus rex and Stegosaurus: the giant jaws, the spiked tail, the roar. It has appeared in countless films, toys and picture books, and it never happened. It could not have happened. The two most famous dinosaurs of all were separated by a stretch of time so vast that T. rex is actually closer to us than it ever was to Stegosaurus. The fight of the century is late by roughly eighty million years.

Start with Stegosaurus. According to EBSCO’s Research Starters, it thrived during the Late Jurassic period, around 150 million years ago. It was a plant-eater about 9 metres long and up to 3 metres high, with rows of triangular plates along its back and spikes at the end of its tail, known as thagomizers. It fed on low-growing plants such as ferns and cycads, and its fossils have been found mainly in North America.

Now Tyrannosaurus rex. National Geographic places it around 68 million years ago, in the late Cretaceous period, living in forested river valleys in western North America. It grew to about 12 metres long and weighed several tonnes, and it both hunted living animals and scavenged carcasses. The San Diego Natural History Museum describes T. rex as living at the very end of the Late Cretaceous, about 68 to 66 million years ago.

Put those dates side by side. From around 150 million years ago to around 68 million years ago is a gap of roughly 82 million years. T. rex, meanwhile, disappeared about 66 million years ago, when, as National Geographic describes, an asteroid or comet the size of a mountain slammed into Earth. That means only about 66 million years separate us from the last T. rex, fewer than separate T. rex from Stegosaurus. In the long story of dinosaurs, T. rex is practically our neighbour.

It helps to picture just how long these animals lasted. A study reported by the San Diego Natural History Museum, and published in the journal Science, estimated that T. rex persisted for about 127,000 generations, with around 20,000 individuals alive at any one time, adding up to roughly 2.5 billion T. rex over the whole history of the species. Even that long run fits comfortably into the gap that opened after Stegosaurus.

The mix-up is easy to make, because we tend to squeeze the whole age of dinosaurs into one crowded scene. In reality it lasted for many tens of millions of years, and different dinosaurs lived in very different worlds. So when you see a stegosaur and a tyrannosaur facing off on a lunchbox, enjoy the drama, but remember the truth: by the time the first T. rex hatched, Stegosaurus had already been gone for tens of millions of years.