Tyrannosaurs Were Human-size for 80 Million Years
T. rex's genus was slow to grow, review finds.
"Ten years ago we only knew about five or six different tyrannosaur species, and they were all very similar—giant apex predators like T. rex," said paleontologist Stephen Brusatte, a Ph.D. student at Columbia University affiliated with New York's American Museum of Natural History.
"Now we have 20 tyrannosaurs, spanning a hundred million years through the Jurassic and Cretaceous," said Brusatte, who co-authored the new review.
"They range in size from small dogs all the way up to T. rex," which could reach 40 feet (12 meters) from nose to tail tip.
(Related: "Tiny T. Rex Ancestors Achieved World Domination.")
Tyrannosaurs originated in the Middle Jurassic period, about 165 million years ago. Though they generally remained small for 80 million years, early tyrannosaur